Charge two equi-voltage Ping packs with one charger?

[chvidgov.bc.ca]

Is it safe to charge two 48V 15Ahr Ping packs which were...

a.) Balanced/Fully Charged (separately, two chargers)...then...

b.) Discharged simultaneously through an ideal diode, resulting in very nearly same level of discharge on the two packs...then

c.) Connected to one charger, through a "Y" harness, no diode. IS THIS SAFE?

As the first pack reaches HVC, then the second will keep charging, but the charger will still be delivering voltage to the pack which would normally (at HVC) have the charger shut off...for a while, then the second pack would reach HVC. THEN the charger is shut off...

I suppose the process might hold both packs at the same voltage as they charge so that they both go "16 LED on" HVC on both BMSes at very nearly the same time?

The reason I ask, is that I'd like to just take one charger with me on a trip...even if I have to wait a bit longer to get to full charge state on both packs...

 

[dogman dan]

I dunno. Seems to me like each bms would handle any overcharged cells as it finishes. Seems like you wouldn't need diodes to seperate two charger inputs.

On the other hand, charging together would never result in less charge time than charging seperately. The chargers rate is what it is. So two chargers will just charge faster. Charge one, then the other should work fine, provided you are awake. But a hassle if asleep at the change over time. You'll feel foolish, if caught out with one charger that stops working.

What about just paralelling the packs at the main wires, before the bms?. Then no need for diodes, and a weaker pack can support the stronger one better. Then discharge and charge through just one bms. The "slave pack" bms would still do the discharging if needed at the top of the charge.

 

[dnmun]

no need for diodes, ideal or otherwise. you can connect the two packs in parallel P- to P- and you can charge both together by connecting the C- leads together also. you will need to disconnect the P- leads from each battery while charging.

diodes should only be used when they are needed. not needed here at all. ideal or degenerate, neither one is needed.

 

[chvidgov.bc.ca]

Actually I wasn't going to use diodes. I do discharge through a diode, and that use of two packs (whether dioded or not) stresses the packs less, as each is run at half the customary C-rate and I get way better torque with two packs contribuing. And I understand it would take twice as long to get the combo back to a full charge with just one charger. But I'd like to keep the two packs at the same charge state at all times so I can use them both at any time, not needing to switch over when Pack 1 dies. I was going to charge them both back up (as opportunity permits) through a non-dioded Y connector (aka parallel I assume) with just one charger going to both BMSes C- through the Y. My concern is around the point where one pack has just finished charging and the other hasn't, if that would damage the first pack to arrive at fully charged, with the second one a bit lower.

I've set up the packs to be removeable and modular for use with other bikes as well as this parallel config on the trike, and also the charger leads are inside the battery cases, so I have to remove the case from the trike and open the lids forcing the bms'es to get more "airtime" cooling-wise as I charge, so I wouldn't be able to connect the P-s before the BMSes. I do like the diode as well, as I will never have to worry about hooking them together accidentally in different charge states. I'm sure I could get away without it in 99% of the situations, but if one of the packs makes a bad connection from a backed out Anderson pin, they will get out of sync charge-state-wise. Which occasionally occurs on my bikes or packs, that an Anderson gets flaky.

Another variable is that I'm going trike camping this weekend with a buddy, and I've got 2 packs on each trike, and only three chargers. I'd like to just take two chargers, and spend some time playing chess in a coffee shop fifty miles from here.