Tapping a serial connection for parallel charging

H

hj2095

10 mW
Joined
Nov 4, 2014
Messages
33
Hi, I have a question. I have a battery system for my ebike where I have six 3s 3700 mAh batteries in series, and each of these series packs is connected in parallel (four in total). I'm trying to figure out a way to charge these batteries without having to plug and unplug all of my deans connectors each time. My question involves the tapping of each individual 3s battery. Is it okay to place a tap on each battery such that I can parallel charge six at a time without having to unplug them from their serial connections? More specifically, would leaving the batteries in series plugged up to my eBike (although the E bike power is off) present a problem when I go to plug in the taps for the parallel charging? Or stated another way, can you tap each battery to charge in parallel, while they are still connected in serial even though there is no active power flowing through the system because the motor is turned off? I apologize for the wordiness, but let me know what you think.
Thanks

H
 
The series connections will short out batteries when you make the parallel connection. You have to disconnect the series connections before making the parallel connections, or use isolated modular chargers instead of parallel connecting to a single charger.
 
your battery is 18 (6x3) series 4 parallel right?

you can charge as many cells as you like, as long as you respect the series connections


you could use a 6s charger to charge 2 o the series strings at the same time

or use 3 x 6s chargers to charge them all at the same time ?
 
Actually I am balance charging the batteries, and I do have 3 6s chargers, but I'm not sure how to connect the 18s series packs. Thanks for the help. Right now I disconnect each 3s pack from the series and plug it in to balance charge in parallel. I suspect there's a better way though.

H
 
Maybe make sets of Deans 3s to 6s series adapters. 6s for charging ease. 4mm bullets or Andersons on the ends to make connection easier. Make 3 6s4p units like the one pictured. The red and black connectors for each 6s4p unit--those are your charging "taps." Now that you have 3 chargers vs. the two the last time you asked this so you can charge all three in one pass. Reconnect the three units in series after done charging to make 18s.

hj2095-6s4p-need3.png
 
Given that you are charging 6s, it makes more sense to me for you parallel first. Then you just unplug two plugs, and you have three 6s packs ready for the charger.

Yes, it takes more plugs and connectors than series first. But if you need to break it up to charge, it's the way to go IMO.
 
Unfortunately you have to break the packs.
I thought about making some kind of automatic system where a set of relays would break the pack and connect the charger automatically.

The problem is they would need to be very high current and that would add weight, cost, and losses...

I believe this is why people use a bulk charger and rely on a BMS to balance. (which I loathe....)
 
If you're not doing any cell monitoring during discharge, there's no need to connect the balance taps at all until you charge.

Several people on ES have setup their bikes so that there is a single connector port containing all of hte main + and - wires from each pack, and use two jumper cable blocks to connect them up. The first connects them in series for discharge, and the second connects them in parallel for discharge. Since the block comes off or on all at once, there's little risk of accidentally shorting anything out--all that has to be done to ensure that is to connect all of the balance plugs to their appropriate paralleling blocks only during charge, and remember to remove that for discharge.

To completely eliminate that risk, if you use a single connector for the jumper block that *also* has all of the parallel connections in it for charging, but simply leave them all unconnected in the discharging connector, then whenever you pull teh block/connector for charging off, all parallel connections are automatically cut.

If you can't or don't want to use a single connector for everything, then mount mulitple connectors on a plate or box, one set on the bike and one set on your charging cable, and one set on the discharging block. Then again you can't accidentally hook something up for charging and leave it on when you go for a ride, because you stil lhave to remove it all as one block in order to put the discharge block on there.

The discharge block doesn't have to have any of hte balance connectors actually installed, just physically block their pins on the bike so you can't accidentally short them with anything, and/or to make that part weatherproof if it's externally exposed.
 
you always want to parallel before you series


after that, buy the leads to parallel all the balance tabs, and have an extra balance tab coming off each parallel string

than use those extra ones for charging


job done, nice and easy
 
Since hj2095 will have to solder 24 Deans connectors he might as well parallel first like everyone suggests. For an easy to use charge and discharge connection scheme using blocks of Anderson connectors see Dogman's icecube57 harness review.
 
NOT always parallel then series connect. But yes, for his chargers, it will work best.

If he could charge at 18s, then he'd use a lot less connections to series first. But a better connector for that might be large bullets.

To eliminate some of the plugs in a parallel first setup, you can use crimp sleeves from the hardware store to crimp 3 pack wires to one wire, and use only the one plug after the 3 into 1 connection.
 
dogman dan said:
NOT always parallel then series connect. But yes, for his chargers, it will work best.

If he could charge at 18s, then he'd use a lot less connections to series first. But a better connector for that might be large bullets.

To eliminate some of the plugs in a parallel first setup, you can use crimp sleeves from the hardware store to crimp 3 pack wires to one wire, and use only the one plug after the 3 into 1 connection.
Click to expand...



when would you series first then parallel on an ebike ?
 
Sorry I didn't make that more clear when you would series first. Mostly, when you can charge the entire pack at once. So you have a 12s balance charger, or a 20s bulk charger, or whatever.

If you can charge the entire pack without disconnecting anything (using the rc packs), then you get 3p 18s, or whatever with less plugs. Less plugs, less places you can have a problem with a plug. And you can still remove a pack to replace it, or just balance it separately anytime, easy.

To use less plugs with a parallel first pack, you cut off plugs and make permanent connections that make it hard to remove a single pack.

Right now in my own stuff, I kind of do both. I have 14s 25 ah. (5p) But I use it all kinds of ways on multiple bikes. So I have 2 packs that are 2p 14s, and one pack that is 1p 14s. When needed, I parallel it all, and have 5p 14s. The 2 p packs are paralleled first. Why? Because before I started bulk charging I did break packs into 6s or smaller to charge. So I have this huge pile of 2p adapter plugs laying around that I made up years ago.

Now 99.9% of the time I bulk charge with various 48v lithium chargers. So I never break out a 14s pack smaller to charge. I charge in a place I make a fire all the time, my fireplace.
 
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