Charging single Headway Cell, best way?

[Spacey]

I'm thinking that I will run my 60V pack without a BMS and every month drain the whole pack down to 20% capacity then Charge each cell individually to 3.3 or 3.6v so as to balance the pack.

Does anyone have any idea of the best chargers for single Headway cells? It says on the cell specification that charging voltage is 3.65v and that nominal voltage is 3.2V.

I have a few phone chargers around but they put out 4.2volts.

 

[Spacey]

Found this:

http://www.cloud9vaping.co.uk/epage...bjectPath=/Shops/yxve46fvrnud/Products/B56-08

 

[adrian_sm]

Charging single cells is just too slow and painful. Especially using slow chargers like the one you linked to. I would avoid it if at all possible.

Why not add a few extra wires to your pack so you can charge it with a balancing RC style charger. Here is a link to a nice one that can do 10 cells in series.http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6609

- Adrian

 

[Spacey]

Cheers for the reply Adrian, so this unit could charge 10 cells at a time and drain/charge each individual cell to a balanced voltage?

Hmmm that really would be a lot quicker.

 

[dnmun]

why not just run with a 48V BMS since then you can use a regular 48V charger?

 

[The Mighty Volt]

A slow but accurate way of charging each cell is to use a switching supply with a display.

Set your system to run C.V from 3.6v and attach the terminals.

A dead cell will probably pull the maximum current your machine can put out.

If the cell is below or at 2.8v it will draw CC CV initially. Once it reaches 3.0v it will then draw a diminishing rate of current whist charging, CV.

It's a bit like pulling a pint of guinness. Initially there is a surge but the closer the pint is to being finished, the less is added. Eventually it is drip-drip-drip.

I hope that makes sense. I did this when I was charging all of my cells before joining them in parallel.

Cheers.

 

[Spacey]

why not just run with a 48V BMS since then you can use a regular 48V charger?

Because even with the working BMS that I have, when the charger stops you can see several red lights come on the BMS....all good.......then when they go out the charger starts up again.....great working as it should............

But that's it, no more discharge the charge cycles. I don't know if it's because of the BMS I use but leaving the charger on all night I never hear it start up again after the first restart so cells not really getting balanced. I just thought that for me not having the hassle of a BMS would be fine as long as I leave 10 to 20% in the pack on discharge and then maybe balance the pack manually every couple of months.

 

[adrian_sm]

You dont need to discharge cells and recharge to balance them. Just not over charge cells, while bringing the low voltage ones up to the required voltage.

Have you measured the cell voltages at the end of a charge. Your BMS may be working properly.

The style of charger I linked to before balances the cells without drain/recharge cycles. But it can also do automatic drain recharge but this is only really necessary for "breaking in a pack" and checking cell capacities.

- Adrian

 

[jondoh]

I also agree that it would take too long to individually bring up each cell from 20%.

Johnrobhomes has figured out a way to move the bms to charger. Let the pack balance and after it's done, immediately unplug.

I use a power supply to "top off" cells. I let the bulk charger charge the pack. I check the cells while the pack is being charged right before it finishes to identify the lower voltage cells. I set the power supply to 3.65v and 2 amps. So for example, I'll have 3 cells that are about 3.4v while the rest are 3.65 ~ 4.2 fresh off the charger. I'll charge the three cells individually to check where they are relative to the rest of the pack. It usually takes about 10 minutes at 2 amps to bring these cells up to 3.5 volts and maybe a few minutes more to get to 3.65v. I have observed that at the end of charge, you see what appears to be large difference in voltage 3.4 ~ 4.2v but the actual difference in amp hours is relatively small. Lifepo4 cells are pretty sensitive to additional current near the end of charge. I don't believe we should be too worried about the differences in voltage at the end of charge. As long as they're between 3.4 and 4.2, i'd say the pack is fairly balanced.