10A charger for 120V?

[__Tango]

Hi folks.

I'm trying to get a charger for my pack of 36 Thundersky 60Ah LiFePO4 batteries in 36s1p. I found a (King?) charger being sold by BMSBattery.com (which is ecitypower.com, also on ebay as ecitypower). It's 1500W, so it'll do 120V nominal at 10A, and they say that they can specify the proper output voltage for my pack. It is a CCCV charger.

At those voltages, it is about 10A. Someone mentioned to me that 10A isn't "big enough" to charge my pack and that i should go with the 2000W version from them, which would be closer to 15-16A.

I always thought the lower amp rating for a particular voltage meant a longer charge time...not that it wouldn't work. Am i wrong about this?

I'd like to stick with the 1500W charger since the 2000W is more expensive, and the added size/weight makes it less desirable for putting in an electric motorcycle (which is what my project is).

Any tips would be helpful...

Note, i will be using a Fechter/Goodrum BMS, so i'm not worried about it "only" having a simple CCCV curve.

Thanks a bunch!

 

[mwkeefer]

Tango,

Charging a 60 AH pack using a 1500w charger would work out as follows:

1500w / 120 = 12.5 A

Assuming their charger is 80% efficient (this is actually rather low a rating, your so close to line voltage and it's been my experience that the closer you get to line voltage the more efficient the conversion - given the properly wound transformer).

At 10A it would charge your pack fine... the CC/CV bit is actually important regardless of if your using a GGoodrum Fechter BMS or not, basically it's simple:

The charger will be set for the Cell Charge Voltage (I'm not sure what yoru cells charge to, assuming 120v for the pack of 36s then 3.33v is what you expect to charge the cells to?) * Cells count in Series.

If you were doing this the "down and dirty way" (no reason not to) then you would simply need to configure a power supply to produce 120v without a load attached (tested using DVM or somthing). The CC/CV part simply means that the output voltage will drop down to just above your packs resting (empty?) voltage and then provide 10A (or whatever current it's calibrated for) until the pack gets really close to the voltage setting and then the current will begin to taper off.

The proper technique for LiPo (sorry not an A123 guy) is to taper to C/20 or capacity, in your case that would be when the current going into the battery was at 6A (which does sound a bit fishy to me) - this is one thing I always get messed up and it may be Charge Rate / 20 so for you it would be when the current draw reaches 250ma (10A / 20 = 250ma).

The BMS from Gary and Fechter will handle the process of equalizing the cells as they enter the tapering stage (I think, the design has changed a few times and I am dying to get my hands on one just to get rid of the spaghetti mess I have cobbled together to acheive a similiar function)...

That said... at 10A and assuming you only run your packs down to 30% remaining... it will still take 6+ hours to charge (depending on how out of balance the packs are).

I would be very curious to learn of your experience with BMS Battery if you indeed go with the purchase!

another option (possibly lower cost) would be a few Meanwell S-350-24v units in parallel turned up as high as possible... that would be good for a 15A charge and cost around 150.00 (I think).

Hope it helps!

-Mike