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Playing with batteries...

Old 11-15-2012, 12:34 PM
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Playing with batteries...

Not the best images, but they will have to do...

The size is 153x80x80 vs the stock VTR battery at 150x133x87... But they pack a mean punch... 10 Ah of LiFePO4 power... I tried them on the slightly built Hemi a minute or two ago, and it liked them, fired on the first tickover...

The endcaps are made by cheap delrin cutting boards from IKEA, about $1 worth for each, and some basic supplies of M3 screws and nuts... Took me a full half hour to make... And that's with about 16 of them made assembly line style...

You can probably short them out if you work at it, but they aren't made to be dummy proof, only to protect the connectors during normal usage... I wouldn't recommend shorting them though, I tried that a while ago with smaller cells, they melted my favourite screwdriver...

These will start a VTR down to around where the oil goes semi-solid... Or in my case, my tractor for clearing snow...
Attached Thumbnails Playing with batteries...-2012-11-15-20.55.22-1.jpg   Playing with batteries...-2012-11-15-20.55.33-1.jpg   Playing with batteries...-2012-11-15-20.55.40-1.jpg   Playing with batteries...-2012-11-15-20.55.45-1.jpg  
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Old 11-15-2012, 03:51 PM
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Nice cheap and strong battery... looks good, ill be getting some lifepo4 cells at some point this winter for my rebuild
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Old 11-15-2012, 09:43 PM
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For a minute I thought you were producing these assembly line style to sell to the forum at deep discounts.

Ikea boards are delrin?
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Old 11-15-2012, 11:14 PM
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Originally Posted by smokinjoe73 View Post
For a minute I thought you were producing these assembly line style to sell to the forum at deep discounts.

Ikea boards are delrin?
Actually, I am making them and selling to Swedish forum members... I can just as easily sell them to you guys, but I doubt I can compete in price with the ones sold on Jamie Daugherty's site when you add shipping... I make this type, which is more suitable for larger bikes really, and the smaller ones for the VTR...

Yep, hard to make sliders though, since they are flat... But works nice for this...
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Old 11-16-2012, 07:17 AM
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Did you get a discount making them in bulk? Maybe a human on this side of the water would want to order a round and make some... or at least price them out to see if it would be worth it...

That's more than double the Ah of the 8 cell A123 ones that are on Jamie's site (and happen to be in my bike).

I have an IKEA almost walking distance from work...
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Old 11-16-2012, 07:25 AM
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Its good to know since on my racebikes I have made delrin slider for all contact points on the fairing and radiators.. Saves alot of repair work.
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Old 11-16-2012, 08:06 AM
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It would be funny to see a Hawk with cutting boards as sliders on the sides Imagine that? But maybe if you cut them in creative shapes it could look and function great.... Just a thought! Also think of how many sliders you can make from a single board...
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Old 11-16-2012, 08:11 AM
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Originally Posted by Tweety View Post
Actually, I am making them and selling to Swedish forum members... I can just as easily sell them to you guys, but I doubt I can compete in price with the ones sold on Jamie Daugherty's site when you add shipping... I make this type, which is more suitable for larger bikes really, and the smaller ones for the VTR...

Yep, hard to make sliders though, since they are flat... But works nice for this...
Tweety, how easy do you think the Hawk's charging system can charge a battery this size? Doe's it present potential issues?
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Old 11-16-2012, 12:50 PM
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Originally Posted by NHSH View Post
Tweety, how easy do you think the Hawk's charging system can charge a battery this size? Doe's it present potential issues?
Nope, none at all... The stock lead lump is 10Ah, these are 10Ah, so technically it's a direct replacement... In reality these packs have about 100 times the starting attempts of a stock battery, is back up to a full charge after a couple of blocks of riding, since they can soak up to around a 10A charge current, and they will start the bike unless the oil is frozen solid, or the pistons are stuck... Just mind the tools, they are temperamental if poked...

Like with all LiFePO4 batteries, you will want to make certain that your charging system is operating at spec... It must, at all times never, ever exceed 14.5V and it should never, ever drop below 13.5V... Ie, go though the wiring and get a Mosfet R/R, and you are good to go...

The only "snafu" is that the connectors are on the side, so I highly doubt that the stock wiring will reach, but it's a non-issue if you use a short lead with Anderson connectors like I do... Makes it easy to disconnect for storage (and it's great to make it harder for thieves)... There is ample room for the wiring in the box, since it's around 2/3 the height of the stock battery...

Yeah, I bought a big batch at a discount price, but not that much, so as long as you buy 16+ cells you get a decent enough price really for making a pack for yourself and a friend or two... Just keep in mind, the 10Ah cells fit's in the stock battery box, the 12Ah or 15Ah cells are too tall to fit for the VTR...

Last edited by Tweety; 11-16-2012 at 12:54 PM.
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Old 11-16-2012, 02:03 PM
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Hey Tweety,
I've been considering having RB Batteries build a battery for my car ('99 Lexus). I've had a fair amount of communication win Dan Gregg about it. The main reason I have not done it is due to concern about the charging system in the car. Dan told me that if the battery charge gets too low, the charge current can kill the battery. They can also die from deep discharge only.

Do you have any suggestions for modifying the charging system to be compatible - and stupid-person-proof? Or is it less of a problem than I am making it out to be?

thanks for any advice you may have.
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Old 11-17-2012, 12:40 AM
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Well, the information you have gotten from Dan is absolutely correct, albeit a bit incomplete as you retold it at least...

Lets start with the easiest part, deep discharge cycles... This kills the cells the same way that it kills a lead battery, only much, much faster... When a lead battery is discharged beyond spec, it starts to corrode the lead grid that is the poles... In a lead battery, there are several pounds worth of lead to corrode, so it takes a fair amount of deep cycles to make a noticable differece... The LiFePO4 cells doesn't corrode, instead they form crystallines in the gel like fluid that "shortcircuits" the rolled up conductor, so essentially one or two crystals can short out the entire cell...

There are two things you can do to make sure not to kill your cells... One is easy and cheap, the other takes a bit more work/money and is only neccesary if you are using 8+ cells... (To keep the paranoid one's from going overboard with their bike batteries...)

One, get a battery disconnect... When the car sits idle for a while, disconnect the battery, to keep it from draining... Little things like a dash clock and such are the enemy...

Two, get a very basic BMS (use here as Battery Monitoring System) that cut's of the battery automatically if one cell drops below the discharge limit... I can build one for you, or supply the schematic to build one... On a bike this is completely pointless, even as a daily rider/whatever... It adds weight and bulk, and all it does is protect the cells from deep discharge, something that never happens with daily usage, or if you use a disconnect... On a car using the smaller cells, and using a lot of them to get the Ah up, it might be useful though...

The other statement, about the charge current killing the cells, are a bit more complex... The cells can at any time accept up to 3A charge (small cells, 5A large cells) and in good conditions more than that, by a wide margin... But if the cells have dropped into deep discharge, below the knee of their discharge curve, and one or more cells are essentially "empty" while the others are just "low", a high charge current will force one cell to charge the other to equalize, making the "empty" cells reverse polarity... At that point, those cells are trash, and are also slowly killing the rest of the pack... A BMS like mentioned, takes care of this problem, as it never allows a cell to drop beliow the knee, and instead cuts the pack of until it's recharged... At this point, I'd recommend charging the cells individually by the BMS leads, until it's back in balance, and ready to deal with the cars high charge current...

Please note, this is with us talking about the smaller cells, the same as i built packs for the VTR's with, and the same as Dan built bike packs with... If those are used for a car, you have to put them in paralell, which creates this scenario where one cell can reverse another... With 8 cells, I instead matched up the two cells in paralell, by testing them a couple of charge cycles, and putting them two and two in pairs that would deplete at roughly the same time... That way, no BMS is ever needed, when one cell is "empty" it's partner is also empty, and the cell voltage drops enough that the battery can't start the bike, and you charge it normally, maintaining cell polarity... It's only when 3-4-5 cells stay in paralell, maintaining the pack voltage despite one cell being depleted you risk reversal...

With these larger cells, you could probably use 4 of them if the car is a "toy", or as a daily driver, an 8-pack... Then the same principles applies as in the bike, match them up, don't be overly stupid, trying to crank the car to death and you never need a BMS... I'd still recommend the disconnect though, and checking the charge voltage before hand so you know the battery will be happy with your charging system...

Longwinded... Sorry...

Last edited by Tweety; 11-17-2012 at 12:46 AM.
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Old 11-17-2012, 01:51 AM
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Using my own images from another thread...

How you pair up matched cells...

Playing with batteries...-pairing-cells.jpg

Top balance, the bad way of balancing...

Playing with batteries...-top-balance.jpg

Bottom balance, the expensive way of balancing...

Playing with batteries...-bottom-balancing.jpg

Self balancing, the smart way...

Playing with batteries...-self-balancing.jpg

Last edited by Tweety; 11-17-2012 at 01:55 AM.
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Old 11-17-2012, 11:37 PM
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Good stuff. Thanks. I would like to know more about the battery monitor, so that in case I leave the car sitting for a couple of weeks, the battery doesn't get low. I suppose some extra amp-hour capacity would make that problem go away, if it's just sitting for 2-3 weeks.

I don't understand what you are talking about regarding matching the batteries and balancing.

Dan was also concerned about cranking in cold weather. He suggested turning on the headlights for a couple of minutes to warm up the batteries, before starting the car.
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Old 11-18-2012, 12:44 AM
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Originally Posted by RCVTR View Post
Good stuff. Thanks. I would like to know more about the battery monitor, so that in case I leave the car sitting for a couple of weeks, the battery doesn't get low. I suppose some extra amp-hour capacity would make that problem go away, if it's just sitting for 2-3 weeks.

I don't understand what you are talking about regarding matching the batteries and balancing.

Dan was also concerned about cranking in cold weather. He suggested turning on the headlights for a couple of minutes to warm up the batteries, before starting the car.
If the car is sitting for more than two weeks, and you know it will be before hand, use a battery disconnect...

That is a much better idea than relying on a BMoS which still means that you will be storing the battery in discharged condition once it has cut out, which is bad for the battery... Ideally it should be charged immidiately, in reality storing it discharged for more than a week is about a 10% chance to kill it... Or make the BMoS cut out while the cells still hold a charge... Then you will need a "big" battery, but that's one option...

Actually, cold weather cranking isn't an issue... Yeah, if you warm the pack up, it cranks easier... But it warms itself on current draw, so you just have to crank a few more times in the cold, which isn't an issue as long as the pack is large enough...

What specs are the stock battery for that car?
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Old 11-18-2012, 01:08 AM
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BMS can mean two things, either Battery Management System, like in an electric car, where a computer takes care of the battery, regulates charge and discharge to keep it at optimum... Or Battery Monitoring System, which means it's just keeping an eye on things, either displaying it to you on the dash or similar... I like to add the BMoS and BMaS to differentiate the two...

Or in this case something inbetween, where the BMS burns off the current if it gets too high on charge, and essentially disconnects the battery if one or more cells drop below a set voltage... What you need for this to work is a lead to the pole on each cell, so it can measure the cells individually... Then you need a battery disconnect that can be operated by hand or by "remote"... Essentually the BMS completes a circuit, and the battery stays connected... If it triggers an undervoltage, it trips the disconnect, and the battery is cut off...

The result is, you cannot damage the battery... The downside to a "crude" system like this, is it can potentially leave you standed, since it will simply switch the car off if there is a problem... So, it should really be complemented by a dashboard readout, or an **** driver/user that disconnects the battery once the car isn't in use, and checks it "pre-flight" to know the condition of the battery...

A good storebough system that does this will cost you about $2000-3000, and is mainly designed for 10+ cells... You can build one for around $100 that will be just as good for 4 to 8 cells... IF you decide on using 4 or 8 of the larger cells, either buying from me, or buying them yourself, I'll gladly make you one for around that price... If you go for the smaller cells, it becomes too involved, and buying one is a better option, as well as the battery then being less robust for car use...

But my honest opinion still stands... Get 8 large cells, and a standard battery disconnect... Don't let the car sit for more than a week without switching the disconnect, and don't ever use a charger on the pack, and I can pretty much guarantee that it will never, ever be an issue... Making it more complex isn't always better... The KISS principle applies...
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Old 11-18-2012, 01:17 AM
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I'm breaking it up in posts too keep it readable...

About the balancing and matching cells...

Top balancing, like is shown in the image, is what a dedicated charger does, it makes all cells completely full, and you start discharging from the top down... That means that the weakest cell runs out first, when the others are still supplying power... End result is a dead cell...

Bottom balancing is what an expensive BMaS & BMoS does... It knows how much to charge to keep the weakest cell topped of, and since others aren't completely full, every cell is depleted at the same time... You lose a % or two in usage, but you aren't killing cells...

Self balance is what happens if you have a healthy charging system, and just use the bike or car, making sure to never ever fully deplete the battery, and never ever put a charger on the pack... If you drive the car, then disconnect the battery instead of letting the car sit and slowly discharge the battery down to dangerous levels, the battery is always 70-90% charged, and once you then start the car again, in a few blocks you have regained that charge and the battery stays in the "safe range" at all times, so no BMS is really needed...

The caveat to the last scenario, which is the same as how a SLA battery is treated, is that in the same way you then need to have a large enough pack to have a margin of error... Otherwise it's easy to go outside the "safe range"... A note here, 8 large cells is more than enough for any car in fair weather... I'm using one on a big old hemi lump... Unless we are talking about a 200 Ah+ stock battery, it should be enough for your car in any weather really... Or, you could just kill a mosqitou with a cannon, and do a 12 pack... That should be more than a fair margin on any car...

Last edited by Tweety; 11-18-2012 at 01:23 AM.
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Old 11-19-2012, 01:37 PM
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Originally Posted by Tweety View Post
Actually, I am making them and selling to Swedish forum members... I can just as easily sell them to you guys, but I doubt I can compete in price with the ones sold on Jamie Daugherty's site when you add shipping... I make this type, which is more suitable for larger bikes really, and the smaller ones for the VTR...

Yep, hard to make sliders though, since they are flat... But works nice for this...
Markus,

How come JD (Motorcycle Batteries - RBbatteries) does not recommend his batteries for -40F? I have not checked with him but for V-twins (like the VTR?) he recommends the 12 cell unit, and it costs $150.

How much would it cost here if you made me one (8 or 12 cell)? JD's only have a 90 day warranty anyway.BTW, how is the new abode?

Has SWMBO convinced you to start trying to have rug rats yet?
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Old 11-19-2012, 02:15 PM
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Originally Posted by skokievtr View Post
Markus,

How come JD (Motorcycle Batteries - RBbatteries) does not recommend his batteries for -40F? I have not checked with him but for V-twins (like the VTR?) he recommends the 12 cell unit, and it costs $150.

How much would it cost here if you made me one (8 or 12 cell)? JD's only have a 90 day warranty anyway.BTW, how is the new abode?

Has SWMBO convinced you to start trying to have rug rats yet?
Well, at -40F the oil will be thick enough that the engine is unlikely to start anyways... I'd say somewhere around -10F or so is a realistic temperature to start an engine... I have myself used these types of batteries down to -20C which is in that neighbourhood... At that point, the cells needs to warm up to produce any power...

What happens is that they crank very, very weakly at first, but the current self heats the cells, so after a while they pick up speed... That means you need a fair bit of reserve, since you are using power to heat the cells first... I'd say it was a bit marginal with an 8-pack on the VTR once you got below -10C or around 15F... But it works...

So if you are going for all-weather performance on a VTR, and perhaps want to use heated grips and such, I'd say a 12-pack is a great idea... For normal usage though, an 8-pack is plenty, it's what I have been using in my bike... But I usually chicken out and switch to the dualsport when it gets icy anyways, the lighter flywheel along with other mods to my engine isn't great for icy roads, trust me... And the dualsport has one of the above 4-pack of the larger cells, so it's 10Ah, but that's needed with heated grips, dual HID's and a big fricking helmet lamp... It usually see's hard riding in dark woods on gravel and snow... (Mind the frigging tree's! )

An 8-pack is $110 plus shipping, the 12-pack is $145... Haven't got a clue what the shipping is though at the moment... The caveat here is that I have no cells at the moment, I used my last one's so it takes me a fair while to get new ordered... For reference, an 4-pack of the larger cells are only $150... That will be enough for the VTR in artic conditions...

But, there is a easier and cheaper option... I can make the endcaps, and other parts, and send you at cost... Then you order the 4 large cells, which is cheaper than me having them sent here, and then sending them "back" to you... All you do is assemble it, and you got a working battery... Or if you like, I'll PM you info, since I know someone else is working on a little project on your side of the pond, and could perhaps make you a set...

Actually haven't moved in yet... Still in a borrowed appartment, as we fix the kitchen and bathrooms... It should be ready for the move in about 3 weeks though, if I don't screw anything up more than usual... Rugrats have been discussed more than once...

Last edited by Tweety; 11-19-2012 at 02:21 PM.
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Old 11-19-2012, 02:21 PM
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Originally Posted by Tweety View Post
But, there is a easier and cheaper option... I can make the endcaps, and other parts, and send you at cost... Then you order the 4 large cells, which is cheaper than me having them sent here, and then sending them "back" to you... All you do is assemble it, and you got a working battery...
What all parts are involved? This would be very appealing to me, although if I knew how I may make a larger one for the cage...
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Old 11-19-2012, 04:27 PM
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Now I understand.

As long a I don't do anything stupid, like leave the dome light on overnight, I should be ok with a disconnect and no BMS. I probably need an RMS shock collar that "reminds me" if I leave my dome light on. How much would one of those cost?

Dan wanted to build a pack with a minimum of 28 cells (DeWalt power tool cells), but 32 were recommended. I now know for sure I don't want that.

Can you tell me your source for batteries? I diddn't have much luck, when I was looking a few months ago. I'd be happy to send a contribution for your efforts, if you could send me some design information regarding building an 8 pack for my car.


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Old 11-20-2012, 12:24 PM
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My "source" is Headway themselves... And unless you are buying 100+ cells, it won't be of much use, since they won't sell less, but if you order a pallet, the price is very reasonable...

But for an 4 or 8 cells, I'd look on eBay, expect to pay $15-20 per cell... Read specs, there are alot of different one's... If you are building for a bike, 38120 cells are the best fit... For a car, the physical size is less important...

As far as building, I simply used the supplied holders to make a "brick", and then two sheets of delrin cutting board to seal off the ends making them near impossible to short out... One closest to the holder with a large hole, the one on top with just enough to access the bolt, but not letting it protrude... Then I simply took a dremel and made a "channel" for the connector plates, and small bolts to hold the two plates and the holders together, forming a solid part...

The whole endcap comes of in one piece when you loosen the four bolts on the cells... I'll gladly take a couple of pictures of one as it's assembled if you all like...

Making an 8 cell one for a car isn't anymore complicated really... You just make the pattern 2*4 instead of 2*2... And then put the cells in pairs, positive and negative ends connected together for the pairs... That turns 8 cells into 4 larger cells, with the same voltage... Then put them in the holders, alternating order... And connect them up in series, forming one string... Then you get the "terminals" on each end, just like a standard battery...
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Old 11-20-2012, 12:35 PM
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Originally Posted by RCVTR View Post
Now I understand.

As long a I don't do anything stupid, like leave the dome light on overnight, I should be ok with a disconnect and no BMS. I probably need an RMS shock collar that "reminds me" if I leave my dome light on. How much would one of those cost?

Dan wanted to build a pack with a minimum of 28 cells (DeWalt power tool cells), but 32 were recommended. I now know for sure I don't want that.

Can you tell me your source for batteries? I diddn't have much luck, when I was looking a few months ago. I'd be happy to send a contribution for your efforts, if you could send me some design information regarding building an 8 pack for my car.


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Mine's in college already - 2nd year Mechanical Engineering.
Why are you even using the dome light in a way you can forget it? It will make the car hard to start with a lead lump as well... And besides, if you come out one morning, having left the dome on, it won't really be an issue... Just jumpstart the car, and drive like normal, and by the time you get to work the battery is back to working order... Leaving it drained for 3-4 days however is another matter... Then it's really dead...

28 or 32 cells definetly needs a BMS to be practical... And that would equate to ~16Ah and ~18Ah... So 8 large cells is roughly the same as 32 smaller ones at 20Ah... 8 or 32, my answer is easy... And it's probably cheaper too...
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Old 11-20-2012, 12:45 PM
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Originally Posted by 7moore7 View Post
What all parts are involved? This would be very appealing to me, although if I knew how I may make a larger one for the cage...
For the bike, the endcaps plus an Andersson connector and the matching piece to bolt into the bike's wiring, since the stock cabling won't reach with the battery "lying down" in the box... For a cage, only the endcaps, the stock cables should reach...
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Old 11-20-2012, 04:16 PM
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Are those 38120 cells you are using? One of the great things about the push for high power electronics is that we are getting a lot more good performing cells to pick from!
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Old 11-20-2012, 04:41 PM
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Originally Posted by Tweety View Post
For the bike, the endcaps plus an Andersson connector and the matching piece to bolt into the bike's wiring, since the stock cabling won't reach with the battery "lying down" in the box... For a cage, only the endcaps, the stock cables should reach...
Haha, my bike's wiring is anything but stock at this point

Thanks for providing all of the search and install info... makes it easy to pretend that I am able to "custom wire motors". When really it's more just "follow Tweety instructions"
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Old 11-20-2012, 06:57 PM
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Originally Posted by Tweety View Post
Well, at -40F the oil will be thick enough that the engine is unlikely to start anyways... I'd say somewhere around -10F or so is a realistic temperature to start an engine... I have myself used these types of batteries down to -20C which is in that neighbourhood... At that point, the cells needs to warm up to produce any power...

What happens is that they crank very, very weakly at first, but the current self heats the cells, so after a while they pick up speed... That means you need a fair bit of reserve, since you are using power to heat the cells first... I'd say it was a bit marginal with an 8-pack on the VTR once you got below -10C or around 15F... But it works...

So if you are going for all-weather performance on a VTR, and perhaps want to use heated grips and such, I'd say a 12-pack is a great idea... For normal usage though, an 8-pack is plenty, it's what I have been using in my bike... But I usually chicken out and switch to the dualsport when it gets icy anyways, the lighter flywheel along with other mods to my engine isn't great for icy roads, trust me... And the dualsport has one of the above 4-pack of the larger cells, so it's 10Ah, but that's needed with heated grips, dual HID's and a big fricking helmet lamp... It usually see's hard riding in dark woods on gravel and snow... (Mind the frigging tree's! )

An 8-pack is $110 plus shipping, the 12-pack is $145... Haven't got a clue what the shipping is though at the moment... The caveat here is that I have no cells at the moment, I used my last one's so it takes me a fair while to get new ordered... For reference, an 4-pack of the larger cells are only $150... That will be enough for the VTR in artic conditions...

But, there is a easier and cheaper option... I can make the endcaps, and other parts, and send you at cost... Then you order the 4 large cells, which is cheaper than me having them sent here, and then sending them "back" to you... All you do is assemble it, and you got a working battery... Or if you like, I'll PM you info, since I know someone else is working on a little project on your side of the pond, and could perhaps make you a set...

Actually haven't moved in yet... Still in a borrowed apartment, as we fix the kitchen and bathrooms... It should be ready for the move in about 3 weeks though, if I don't screw anything up more than usual... Rugrats have been discussed more than once...
I thought you'd go to the link. By -40F I meant below 40F, not minus 40F.

Regardless of battery (8-123 or 4-LifePO4), what I need to know is the exact procedure and materials that you use to "match up two cells in parallel, testing them a couple of charge cycles, and putting them two and two (x2 in the case of 8) in pairs so they deplete at roughly the same time".

Good luck on the apartment and use the KISS principle with all "remodeling"; I know you have discussed rodents enough to know they are inevitable.
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Old 11-21-2012, 01:53 AM
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Originally Posted by skokievtr View Post
I thought you'd go to the link. By -40F I meant below 40F, not minus 40F.

Regardless of battery (8-123 or 4-LifePO4), what I need to know is the exact procedure and materials that you use to "match up two cells in parallel, testing them a couple of charge cycles, and putting them two and two (x2 in the case of 8) in pairs so they deplete at roughly the same time".

Good luck on the apartment and use the KISS principle with all "remodeling"; I know you have discussed rodents enough to know they are inevitable.
Well... In any case, it works well below 40F, and a fair bit lower...

Eh... As fer matching... Did I mention I'm an EE?... I first cycle the cells 3 times to remove any effects from storage... That's done with a discharge/charge circuit i built, where I can set the cut off voltage for both charge and discharge on each cell indiviually... Then, I run three more cycles where I measure the exact amount of energy going into each cell to reach a full charge... It's all done in batches of 10 cells, and completely automated... I can send the schematic to build the circuit if you like...

But, for anyone not an EE, and freak like me... Cycle the cells at least one time either with a dedicated charger that has the capacity to charge and discharge LiFePO4 cells, like the IMax 6 charger (used for model hobby batteries), or manually by applying a fixed voltage & amperage and measuring the cell voltage with a multimeter until you reach full... And then the reverse, by applying a load like for example a lightbulb until you reach the lower cut off voltage...

Then from full, run them down a fixed amount (about halfway), by attaching a lightbulb or whatever for exactly x minutes... Their exact voltage then is equivalent to the % of their charge... Ie just order them from highest to lowest, and put them in pairs starting from the lowest, and they are now paired up with their closest "buddy"... That means that when that pair is depleted, the whole pack starts dropping in voltage, instead of just one cell...

With 4 cells, this is nothing you need to do at all, just use them... When one cell in the string drops, the whole string drops... For 12V equivalent voltage (3.3V*4 = 13.2V), you always end up with 4 cells, or 4 "supercells" of combined pairs...
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Old 11-27-2012, 07:58 AM
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The selection on ebay has certainly changed, since I was looking a year ago.

What are you using for conducting bars between batteries? I'm guessing the bars for the parallel connections are smaller than for the series connection.

I am considering building some copper cables with soldered lugs for the inter-battery connections and replacing the terminal connectors on the car cables with soldered copper lugs, as well. It worked great with my motorcycle battery.
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Old 11-27-2012, 09:35 AM
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Originally Posted by RCVTR View Post
The selection on ebay has certainly changed, since I was looking a year ago.

What are you using for conducting bars between batteries? I'm guessing the bars for the parallel connections are smaller than for the series connection.

I am considering building some copper cables with soldered lugs for the inter-battery connections and replacing the terminal connectors on the car cables with soldered copper lugs, as well. It worked great with my motorcycle battery.
The bars that most sellers will ship with the cells are fine in terms of conductive mass/cross section and could be used both to connect up two cells in parallel or betwen cells/cell pairs in series... But, and this is a big caveat... It's frigging stainless steel... That's crap for conductivity...

Yes, a copper conductor is a much better option... But no, you really don't need another dimension, and I would NOT advice to use soldered leads for this type of battery... It is well capable of producing enough current to melt a soldered connection or a too thin cable, so that's not a good idea at all...

You could use large crimp connectors and very thick copper wiring, but then you really, really need to crimp them with a proffesional tool, and that's not at all cheap... If you do, tin them with solder after the crimping, to seal out corrosion, and use heat shrink to keep them from shortcircuiting...

A better idea is to get 2 mm or thicker copper sheet and make better bars in the same dimension as the one's you get with the cells... However, to make it easier, if you are stringing up cells in pairs to an 8 cell car battery, I'd make 4 hole bars, ie one large square bar that both connects the cells in pairs, and the pairs in series...

That way, you only have to make tree squares, and two bars with two holes... One bar across the positive pole of the first pair, and a square across the negative end plus the positive of the second pair, another square over the other joint between pair 2 & 3, and between 3 &4, and finally a bar over the negative end of the last pair...
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Old 11-27-2012, 03:17 PM
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I can't see why the current would melt the solder. I would think it would just conduct through it, with negligible resistance. It would only be bridging the gap between the wire and the lug.

But if the wire gauge is too small, that's another story...
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