scootergrisen
100 W
- Joined
- Feb 26, 2018
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Charging two batteries with one charger
- Thread starter scootergrisen
- Start date
I would guess this just has the y-connector built into the cable, and that it isn't actually two separate charging circuits with separate wires. The cable from the Y-point to the charger is no thicker than the two arms of the Y, implying that the wire is the same and that it only has two wires in either arm *and* only two in the main cable.
So...all the caveats about charging paralleled batteries would still apply--they'd both have to be at the same voltage to start with, since you'd be paralleling them (via the charger wires), and be in the same condition, etc. If not, then problems may happen (potentially catastrophic, unlikely but possible).
You'd only know by disassembling the charger to check the wiring and circuitry to see if it is designed as two separate chargers internally, or if it is just a Y-cable pre-attached to a single charger, or some other variation.
So...all the caveats about charging paralleled batteries would still apply--they'd both have to be at the same voltage to start with, since you'd be paralleling them (via the charger wires), and be in the same condition, etc. If not, then problems may happen (potentially catastrophic, unlikely but possible).
You'd only know by disassembling the charger to check the wiring and circuitry to see if it is designed as two separate chargers internally, or if it is just a Y-cable pre-attached to a single charger, or some other variation.
I have two identical batteries wired in parallel, common-port BMS (charge/discharge ports on the same wire from BMS) on each. Charge both batteries at the same time from one charger thru a Y cable. Has not been a problem for years.
scootergrisen
100 W
- Joined
- Feb 26, 2018
- Messages
- 155
Can you show some pics and more info?
Do you charge them like that even they are not charged/discharge the same amount?
Let's say one has a 20% charge and the other has a 80% charge.
Chalo
100 TW
If they're wired in parallel and they stay in parallel, there's no way they could have anything but the same voltage.
If they are put in parallel when they are at different states of charge, the higher voltage battery will uncontrollably charge the lower voltage one until they equalize, possibly damaging them both.
If they're wired in parallel with common port BMSes as stated, then they will not be at different voltages, which means that even if they're different capacites they're still the same SoC.
> So could the batteries not be isolated from each other some how? With diodes or something.
That would be safer, with a diode in each half of the charging Y lead. However you can't prevent one battery hogging all the current so the charger must only be powerful enough for one battery, and overall the charging will take twice as long as with a charger for each battery.
> Suppose you come home late at night and set one battery to charge and go to sleep the next day you wake up to only one charged battery instead of two.
Large batteries like yours would usually come with a slow charger and in one night it may not charge both much beyond half way. A charger's designed to cut off when fully charged by detecting low current, two batteries will take twice the current and it will take longer to cut off if at all, which can be dangerous. Oh and it's widely advised not to charge while sleeping except outdoors.
> Or perhaps have both batteries connected but only charge one battery at a time.
> So when battery 1 is fully charged it would switch to battery 2.
> Or have a timer that switches battery each 30 minutes or so they get charged about the same rate.
This is uncommon with bikes, you'd have to DIY it which (with postage) may come to nearly the cost of a mass produced charger... which is one reason it's uncommon. Your idea ought to be OK but, unlike cars and USB, ebike batteries aren't properly protected to the extent of fully controlling their own charging. The result is a mess for the consumer, needlessly cumbersome, restrictive and exasperating and it compromises safety, but it does facilitate lock-in for proprietary vendors.
That would be safer, with a diode in each half of the charging Y lead. However you can't prevent one battery hogging all the current so the charger must only be powerful enough for one battery, and overall the charging will take twice as long as with a charger for each battery.
> Suppose you come home late at night and set one battery to charge and go to sleep the next day you wake up to only one charged battery instead of two.
Large batteries like yours would usually come with a slow charger and in one night it may not charge both much beyond half way. A charger's designed to cut off when fully charged by detecting low current, two batteries will take twice the current and it will take longer to cut off if at all, which can be dangerous. Oh and it's widely advised not to charge while sleeping except outdoors.
> Or perhaps have both batteries connected but only charge one battery at a time.
> So when battery 1 is fully charged it would switch to battery 2.
> Or have a timer that switches battery each 30 minutes or so they get charged about the same rate.
This is uncommon with bikes, you'd have to DIY it which (with postage) may come to nearly the cost of a mass produced charger... which is one reason it's uncommon. Your idea ought to be OK but, unlike cars and USB, ebike batteries aren't properly protected to the extent of fully controlling their own charging. The result is a mess for the consumer, needlessly cumbersome, restrictive and exasperating and it compromises safety, but it does facilitate lock-in for proprietary vendors.
The two (same size, model) batteries are parallel connected at their discharge ports with a Y-cable, which plugs into the controller. So the batteries are always at the same voltage, same SOC. I leave that Y-cable connected all the time, so the batteries never get a chance to reach different voltages. Even while charging. (Common port BMS.) I did make another Y-cable for the charger (plugs into each battery's charge port) to use for charging because symmetry is appealing to me, but probably technically not necessary?
Correct! ...and it may try to do that at several hundred amps if the voltages are very different. Then your Y-connector goes poof in sparks or a fire. Yes, I charge two of my packs together (14S5P and 14S6P) with one charger but those packs live together and are never separated except winter for capacity testing and top end balancing. I put them back together in the spring at no more than .1 volt difference.
(I see now this is a 2-year old thread???.........)
Last edited:
OP asked for more information yesterday. Doesn't seem like a dead thread.
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