building a booster pack, where to start?

[patpatbut]

Hi all again,

I have a 36v 12ah lifepo4 battery (from BMSbattery) so is it possible to add a booster pack to up to 44v?

Should I get the same cell to build it up? it is a shame as bmsbattery is not selling this cell anymore.

Or should I get 2 of the headway cell and link them in series?

http://www.bmsbattery.com/lifepo4-cell/89-headway-38140s-lifepo4-battery-cell.html

Maybe this?

http://www.bmsbattery.com/lifepo4-cell/625-high-c-rate-10ah-lifepo4-cells.html

Pat

 

[Deleted member 4366]

Do you have the black shrink wrap battery or the aluminium case one? Whichever one it is, it will have 12 cells, so two of those headway ones will give a 17% boost. You can just connect them in series, leaving the BMS to control the other 12. If you have the aluminium case charger, its adjustable, so you can re-set it from 43.8v (or whatever it is) up to 51v and charge all 14 in series, but you need to check that all cells are climbing at the same rate. if they don''t, you'd need to charge the booster cells separately. They should stay fairly well in balance, but you'd still need to check them and balance as necessary. You therefore need a charger that can charge and balance the two of them, so I'd get an Imax one. You should add a 2S balance connector and two power wires for charging. You need to charge them up to the same voltage as the main pack, The imax will look after that, They're normally 3,65v per cell fully charged. Your BMS should shut off the main pack at LVC, so you shouldn't have to worry about that, but you need to check that it's working,and that the Booster cells go down at the same rate as the main pack.

 

[patpatbut]

This is the battery I have
http://www.bmsbattery.com/36v/466-24v-lithium-ion-little-frog-abs-shell-ebike-battery-pack.html

How can I check they are charging or dropping at the same rate?

Pat

 

[Deleted member 4366]

The best way would be to fit a lipo alarm on an extension cable. the main thing is to make sure that your booster cells don't over-discharge before the main pack goes down. Ideally, your booster cells need to be the same type as your main pack. The Headways have a lower resistance than your main pack. I'm not sure how that affects series discharge rates.

This alarm will do the job. The LVC can be set to 2.7v for LiFePO4:
http://www.ebay.co.uk/itm/8S-Lipo-Battery-Tester-Checker-Low-Voltage-Buzzer-Alarm-/290955696228?pt=UK_ToysGames_RadioControlled_JN&hash=item43be4f9864

LiFePO4 cells behave differently to LMC, They go down very fast from 3.65v to 3.3v, then they go down very slowly to 3V, then they start to accelerate downwards, so if you're at either end of the voltage range, a small amount of discharge can make a big difference in cell voltages. There's no point in comparing cell voltages after a couple of miles.

 

[patpatbut]

Thanks Dave.

Is there any sign I can tell when the booster cells start over-discharging?

Would you mind to show me in diagram how to link them together? (with alarm)

thanks
Pat

 

[Deleted member 4366]

Like this. The alarm will beep when they go too low, and you'll see the cell voltages on its display:

 

[patpatbut]

Thanks again. What do you think about the working voltage? I believe it would below the 50v (I use it for S06S)

Pat

 

[Deleted member 4366]

The fully charged total will be 51.1v, but it'll spend most of its time between 46.2v and 42V. 12S lipos are higher, and don't seem to give any controllers any problems.

 

[patpatbut]

Would this charger ok to charge them? (2S headway)

http://www.ebay.co.uk/itm/Genuine-Orginal-SkyRC-IMAX-B6-Digital-Lipo-NiMH-Battery-Charger-12V-5A-Adapter-/330897310942?pt=UK_ToysGames_RadioControlled_JN&var=&hash=item4d0b0444de


Maybe this?

http://www.ebay.co.uk/itm/Turnigy-Accucel-6-lipo-charger-LiPo-LiFe-NiMH-Nicad-UK-/180676231920?pt=UK_ToysGames_RadioControlled_JN&hash=item2a112482f0

Pat

 

[Deleted member 4366]

The first one is only the power supply. Most lipo chargers need one. You can also power them from car batteries or PC power suppliers. The Turnigy one is out of stock.
http://www.ebay.co.uk/itm/IMax-B6-Digital-LCD-Lipo-NiMh-battery-Balance-Charger-UK-Delivery-/350719614615?pt=UK_Sound_Vision_Battery_Chargers&hash=item51a8849e97

http://www.ebay.co.uk/itm/AC-Adapter-Power-Supply-for-LCD-monitor-12V-5A-UK-STOCK-/400414666366?pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item5d3a92ee7e

 

[patpatbut]

Would the turnigy one more "stable" for charging? Just wondering what makes it double amount of the price £15 vs £30

ThanKS
Pat

 

[Deleted member 4366]

There's real imax and fake ones. The fake ones' quality can be variable. I had one that packed up and another that didn't balance properly, so it's better to pay a bit more and get a decent one. In that respect the Turnigy might be a safer bet.

 

[patpatbut]

Bought the turnigy one. Thanks

Can I charge them in series? of I need to charge them individually

Also, where should I get the balance connector that fits the pin of the alarm?

Pat

 

[Deleted member 4366]

You should wire them in series with a balance connector (3 wires) and power wires. You need to use both connectors for balance charging with the Turnigy charger.

here's the improved diagram. Note the orientation of the Deans connectors. You can use the link instead of the booster pack to run it normally in case of problems. With this wiring, you simply disconnect the Deans, and then you can take the booster away for charging.

 

[patpatbut]

Thanks again.

How about the balancing connector? What is the name?

I have seen this on ebay

http://www.ebay.co.uk/itm/like/261327328242?hlpht=true&ops=true&viphx=1&lpid=95&device=c&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=95&ff19=0

Should I get two of this ?

Pat

 

[Deleted member 4366]

This guy's got Deans as well, so you can combine postage:

http://www.ebay.co.uk/itm/Lipo-Balance-Lead-for-repairing-battery-packs-2s-JST-XH-male-2-cell-7-4V-22AWG-/230897695578?pt=UK_ToysGames_RadioControlled_JN&hash=item35c2933b5a

 

[patpatbut]

I have ordered the headway cells and they have a screw on it. Do you know what is the way to link the wire together?

Should I solder the wire to the cell?

Pat

 

[Deleted member 4366]

I guess you need those terminals that are like a washer with an extra bit to solder the wire to whatever they're called

 

[patpatbut]

I have noticed BMSbattery has uploaded the battery cell which used in my battery pack

http://www.bmsbattery.com/lifepo4-cell/656-lifepo4-7070260-polymer-cell.html

I probably use this battery instead. do you know what is the best way of putting them in series? Do I need to compress the cells?

thanks
Pat

 

[Deleted member 4366]

The tags are normally pushed through slots in a PCB, and then soldered, but you can solder them directly together, and solder wires to the outer two. You need a rigid case of some sort for them.