Using a bench PSU to charge Li-ion ?

[Wookie]

I'm thinking of making up a 8 cell 18650 pack (series connections, 28.8v nominal @ 2.2Ah) and using my bench psu to charge it.

Is this possible ? adviseable ?

Setting the voltage limit at 33.6 and the current limit at 1A (or lower) ?

Cheers Howard.

 

[SilverFox]

Hello Howard,

Welcome to CPF.

Your set up looks good, but you will also need to pay attention to cell balance. If one of your cells gets out of balance, you can end up with a cell that is overcharged which could result in rapid venting with flame.

If you do a search on the various RC hobby forums you will find a lot of information on cell balancers. You can use an 8 cell balancer, or periodically charge the cells individually or in parallel to balance them. Balancing is not required with every charge, but it is safer to do that.

Depending on your usage, the pack may stay in balance for quite a while, but if you push things, it may need balancing every 3 - 5 charges.

Tom

 

[Wookie]

You can use an 8 cell balancer, or periodically charge the cells individually or in parallel to balance them. Balancing is not required with every charge, but it is safer to do that.

Depending on your usage, the pack may stay in balance for quite a while, but if you push things, it may need balancing every 3 - 5 charges.

Thanks for that, I'm planning on pulling 1 amp from the pack, stopping when I get to 3 volts per cell when under load. Hopefully within these limits I should get close to 2 hours of power.

I was going to get tagged cells but if I need to occasionally charge them in parallel to balance things, I'll just get untagged cells.

Thanks again for all you help :twothumbs

 

[EvilLithiumMan]

Welcome to CPF.

In my opinion, and experience, there is no way you safely charge 8 series connected Li-Ion without a balancer. Period.

Take SilverFox's advice and learn about balancers.

If you wish to try it without a balancer, then at least you should:
a) verify your homeowner's policy covers you.
b) place an asbestos (or heavy duty) glove and a deep cast iron pot next to the cells. If one flames out, you can quickly sweep the mini-inferno into the pot to contain the damage.

 

[MrAl]

Hello,

These days another word for Li-ion cell is "one half stick of dynamite"

You can also charge that pack inside of a bomb chamber so when it
explodes the chamber will contain the force wave.

Another idea is to charge them one at a time, then connect them
together. I know it's more work.

 

[LuxLuthor]

 

[Avatar28]

Welcome to CPF.

In my opinion, and experience, there is no way you safely charge 8 series connected Li-Ion without a balancer. Period.

Take SilverFox's advice and learn about balancers.

If you wish to try it without a balancer, then at least you should:
a) verify your homeowner's policy covers you.
b) place an asbestos (or heavy duty) glove and a deep cast iron pot next to the cells. If one flames out, you can quickly sweep the mini-inferno into the pot to contain the damage.

You forgot a step,
c) set up a video camera (preferably behind a lexan shield) and when the battery pukes take the video and upload it to youtube for us.

You might also want to consider doing it out of doors or at least in the middle of the concrete floor of your garage with the door open to let the toxic fumes outside and nothing else nearby.

 

[Wookie]

Welcome to CPF.

In my opinion, and experience, there is no way you safely charge 8 series connected Li-Ion without a balancer. Period.

Ok, fair enough, that's why I'm asking questions on here first rather than just going ahead and burning my house down and/or killing myself.

You forgot a step,
c) set up a video camera (preferably behind a lexan shield) and when the battery pukes take the video and upload it to youtube for us.

Sorry I don't have a video camera to record that happening so I might aswell charge them safely.

Where can I get an 8-cell charger from at a reasonable cost ? All the one's I've seen seem to be silly money, but not as silly as burning the house down :thinking:

 

[SilverFox]

Hello Wookie,

Schulze (and I would think others as well) offers an 8 cell balancer that may work out to be inexpensive in the long run.

Tom

 

[NA8]

Speaking of bench power supplies, here's an interesting one I came across. If you did want to use a supply, this might be a good place to start.

http://tuxgraphics.org/electronics/200707/bench-power-supply-unit.shtml