battery wiring question

[drillam]

I bought a 48v lifepo4 battery a few months back and mounted it on one side of a rear carrier on my bike, but find it a bit heavy on one side and am intending to split it into two parts and mount it on each side of a front pannier rack low down on the front forks.
Here's a pic of the battery pack partially opened.

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_9818-1.jpg

As you can see there are 288 individual cells laid out in rows.
Moving from left to right in the picture - rows 1, 3, 5, 7, 9, 11, 13, 15, are wired back to the BMS, whilst the adjoining rows (2, 4, 6, 8, 10, 12, 14, 16) are connected to them by short metal strips. The reverse side of the pack is wired the same way, making 16 wires in a loom going back to the BMS.
My intention is to cut the metal strips halway along each row on both sides of the pack using a cutting disc mounted in a Dremmel tool, then solder them together with a 2m length of 25 way multicore cable I've bought, only using 16 of the wires in the cable.
This should in effect leave the wiring as before but physically split the pack into two more or less equall (in weight & bulk) packs so I can mount one either side of the front wheel.
My question is this :- when I cut through the metal strips do I also have to rejoin the even numbered strips or not?
Thanks

 

[aseb]

I bought a 48v lifepo4 battery a few months back and mounted it on one side of a rear carrier on my bike, but find it a bit heavy on one side and am intending to split it into two parts and mount it on each side of a front pannier rack low down on the front forks.
Here's a pic of the battery pack partially opened.

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_9818-1.jpg

As you can see there are 288 individual cells laid out in rows.
Moving from left to right in the picture - rows 1, 3, 5, 7, 9, 11, 13, 15, are wired back to the BMS, whilst the adjoining rows (2, 4, 6, 8, 10, 12, 14, 16) are connected to them by short metal strips. The reverse side of the pack is wired the same way, making 16 wires in a loom going back to the BMS.
My intention is to cut the metal strips halway along each row on both sides of the pack using a cutting disc mounted in a Dremmel tool, then solder them together with a 2m length of 25 way multicore cable I've bought, only using 16 of the wires in the cable.
This should in effect leave the wiring as before but physically split the pack into two more or less equall (in weight & bulk) packs so I can mount one either side of the front wheel.
My question is this :- when I cut through the metal strips do I also have to rejoin the even numbered strips or not?
Thanks

Are you sure your cable is rated highly enough for the current it needs to carry? Especially as they are using a busbar (You could cut one cell link and trail cables out then measure loading (realistic circumstances- motor under load like hill climbing) using on Ammeter if unsure). You don't want things catching fire.
First result of a google search (*1) said (for a single cell) Nominal Voltage: 3.3v Standard Charge: 10A to 3.6v Max Charge: 10A to 3.6v Max Discharge: 60A (Continuous) Max Pulse Discharge: 120A (10sec) LifeCycle: 1,000+ Weight: 70g

If you mark each side of every cut with an identification letter- first cut A (so marked AA before cut), second cut B- marked BB, third cut C- marked CC, etc then you can join A to A via your linking cable, B to B via your , C to C etc to be electrically equivalent.
One thing that may affect battery balance is the length of the cables- there will be a voltage drop across your connection. I don't know what that might be, or whether it would be sufficient to affect your BMS, but the shorter the linking cable the less effect will be.
Personally I think you should ask your battery supplier, they may be able to help. They may have manufactured such packs to order in the past, more likely than finding ebike users who have done this retrospectively.

If you find out more, please post- it will be interesting and probably helpful to others in the future.


(*1 spec quoted for A123 Systems 26650A LiFePo4 SINGLE CELL with easy solder tabs on google search).

 

[onmebike]

Firstly, this is not a job you should undertake unless your sure of your abilty,
one mistake could prove fatal for the battery and possibly cause a fire in the process. If you do go ahead the only advice I can offer is use as heavy a cable as is practical for the links.
You'll be working with a live battery so be extremely careful.
If I were to undertake this job, I'd be inclined to split the battery along the middle, 2 x 4 rows. This way you'd only need a heavy twin cable to link the two halve's, which appear to be in series. You'll also need to extend the BMS wiring to one half, but those wires are light and carry little current.
Before you even attempt this, try mounting the pack over your front wheel or on your handle bars as is. You'll change your mind once you've tried it. All that weight on the front will make the bike a nightmare to ride. Mounting it low won't make much difference. You'd be better off buying a trailer for it.

 

[Old Timer]

Well I fitted a small front rack with the intention of maybe carrying a spare battery on my aurora. So I just stuck my 13Amp battery on the rack and away I went. Well! I managed OK but I must say that the extra weight over the front wheel was very noticeable and slightly off putting.

On my Evans conversion I hung the spare battery under the cross bar and the balance was near to perfect.

 

[drillam]

Thanks for your responses fellas, it's done now.
cheers

 

[onmebike]

How about a pic of the finished job?

 

[drillam]

How about a pic of the finished job?

OK, but not much to show at the moment as it's still a bit of a work in progress.
Although I've done about 500 miles or so since building the bike I found that the rear end was very heavy and the front twitchy. So I decided to split the battery and place it lower down, one half on each side of the front wheel.
here's a few shots of the battery being split:-

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_0262.jpg

Those short metal joining strips between the long ones had to be cut and a length of wire inserted in their place.
I used a Dremmel but first prised them up from the cells so they wouldn't get accidentaly damage by the cutting disc.

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_0263.jpg

The cut ends were then folded back out of the way.

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_0265-1.jpg

And then the cable soldered into place.

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_0267.jpg

I used a homemade old fashioned type soldering iron, the kind you heat on a flame as I wanted to use a lot of heat quickly when soldering the wires to the metal strips as I reckon there's less chance of heat damage to the cells that way as opposed to farting around for ages with a lower temp iron.
You heat it until the flame coming off the copper turns green, that shows the correct temp. Unfortunately I couldn't hold the camera & iron steady
enough when taking the shots so it doesn't really show too well.

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_0258.jpg

I took your advise and split it lengthwise, a much easier option that I initially planned.

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_0268.jpg

I've knocked up a coupla boxes to hold them to the front pannier racks.
They're big & ugly but are just a temp bodge to see if it all works out.
If all goes well I'll make something out of ally angle and sheet, also probably ditch the foam packing which I put all around it for protection as it makes the boxes too bulky.

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_0285.jpg

http://i14.photobucket.com/albums/a340/drillam/ebike/IMG_0287.jpg


If anyone's interested I'll let you know how it all goes.
thanks
Millard

 

[Old Timer]

I`ve got to say that those boxes look a tad precarious

 

[drillam]

I`ve got to say that those boxes look a tad precarious

only a tad?

 

[NRG]

how does it handle?

 

[onmebike]

I still think a trailer would have been the better option although if you add wheels to the boxes you'll not only have stabilizers but also cut out the need for a stand.

 

[Old Timer]

only a tad?

Maybe a few strings of Onions would set it off

 

[drillam]

It handled a damn sight better than before, dunno if that's a good sign or a bad un though .
I'm taking them off today and reverting to the single battery in the pannier until the materials I'm ordering come though, then I'll build some ally boxes and remount them.

 

[onmebike]

It handled a damn sight better than before, dunno if that's a good sign or a bad un though .
I'm taking them off today and reverting to the single battery in the pannier until the materials I'm ordering come though, then I'll build some ally boxes and remount them.

Why not keep them split between two panniers, must be better weight distribution.

 

[drillam]

Why not keep them split between two panniers, must be better weight distribution.

too much weight at the rear of the bike, it's making the front end real skittish.
The rear mounted motor is quite big, then I have a couple of old BMW motorcycle panniers and a rack, it all ads up.
With the battery split and mounted down low(ish) on the front it was much better.