LiPo: Balance leads connected in parallel 24/7?

[markw]

Hi ES,

There's been a looming question in my head for some time and I really don't know how to research for the answer, so I thought I'd bring it up here.

I'm curious as to what would occur if one were to leave the balance leads connected in parallel (to a tap) 24/7 including during use (discharge) on my ebike. To be more specific, I'm running 20s2p, and it would be much more convenient to leave the balance leads plugged in to a 8x parallel tap permanently, and for bulk charging just plug in that tap to the charger when needed. It would be prudent to cap the end of the parallel tap just in case of pins bending and causing shorts and simply to isolate the pins from each other.

From my limited reading, the idea in theory sounds neat because the cells would equalize eachother's voltages via the charging tap, ie all balance leads for cell 2 across 8 packs would be connected in p, which would help equalize voltage for IR across the packs cells during and after use. I am aware that the balance leads aren't so clear cut, ie for 5s packs there's actually 6 pins, and that pin 1 is cell 1 - and pin 6 is cell 5 + (possibly way off, here, let me know) and that this configuration may impact the outcome I was hoping for.

Can anyone speak for or against this configuration? Any terminology to help fill the gaps or suggested readings would be most welcome. Thank you!

ps. topic icon chosen was the flame... because I'd rather get flamed on ES for being uneducated than flaming my bod, building, or bicycle with a bust battery wiring.

 

[amberwolf]

You can leave any paralleled packs always paralleled, UNLESS they are also in series, becuase the series connection shorts the paralled ones out.

Draw out your proposed setup and you'll see what I mean.

(there's probably dozens of threads asking this question, if you look up titles for "parallel" or "balance", and sort thru the results).

 

[friendly1uk]

Certainly all 20s in one string can be parallel with all 20s of another. Cell after cell. That is perfectly normal.

I have no idea what your going to do with an 8s balance board. They are a great way to start a fire though. Will you be using two and a half boards? I much prefer leads myself, they take less space. Any board is a board too many imo.

The lead supplying the power has the holes, not the pins. They are hard to short out, and won't need any special cover or blind plugs inserted.



If your trying to charge as an 8s, then no, you can't have your balance leads grouped 8s and your cells grouped 20s. Boom.

 

[Ohbse]

If I understand you correctly, you discharge in series, charge in parallel by reconfiguring the wiring. You cannot leave the balance connectors tied together if the discharge leads for the batteries are reconfigured to series. You will create a short and atomise your balance leads/connectors, it's pretty cool to watch actually. The insulation instantly turns to smoke - leaving a momentarily intact but red-hot wire before that breaks and the current flow stops. If the wire is in open air you're probably not going to have a problem but if it's buried in a flammable pack you might have some fire on your hands.

A much better charging solution (this is coming from somebody who reconfigured his packs from series to parallel twice a day for 6 months) is to bulk charge to your final voltage. This is safer in many respects, not least of which is you're messing with the wiring much less. It's easy to make a mistake if you have to change 20 plugs a day, not to mention time consuming.

I connect a single plug and walk away, controller takes care of the rest and balances too. This takes seconds and is very safe.

 

[markw]

Thank you all for your replies! The conclusion I was looking for could be summarized: If your mains are in series, your balance leads cannot be in parallel. I was hoping to keep my balance leads in p while my mains were in series for discharge/bike use, but 100 no's to that. I'll be looking into alternative and safe ways to bulk charge my LiPo and likely report back with questions in a different thread.

@Ohbse I think you have understood my questions very accurately and understand my plight with re configuring batterys EVERYYTIMEEE to charge. I discharge 20s2p / I charge 40s1p. I, like you, reconfigured my packs from series to parallel every day after riding to/from work. I would (with my 15s2p config) use a 1 to 6 parallel lead tap and a 1 to 6 parallel balance tap. 6 unplugs, 12 plug-ins every day. So much room for error but I labeled all my connectors (ie 1 -> 1 .... 2 -> 2...) which I believe saved me from human error at least a couple of times.

Can you point me to any resources you read when learning how to bulk charge? I wasn't aware that bulk charging was done through the controller (ESC?) is that correct? I've seen people with adjustable voltage meanwells bulk charge right through the mains (all in p?), but never through the controller. Do you have a thread of yours I could read through to learn more?

@friendly1uk - Thank you for your reply! I was going to modify my 6x balance tap -- cut open the heat shrink and add connections for two more packs. All the balance wires would be crimped together before the final wire going to the balance plug. I've already burned through one balance board, they are pretty dangerous and generally a bad product.

@amber thank you for your reply too. Reinforcing the important point that balance leads need to follow configurations of the mains.

 

[Ohbse]

@Ohbse I think you have understood my questions very accurately and understand my plight with re configuring batterys EVERYYTIMEEE to charge. I discharge 20s2p / I charge 40s1p. I, like you, reconfigured my packs from series to parallel every day after riding to/from work. I would (with my 15s2p config) use a 1 to 6 parallel lead tap and a 1 to 6 parallel balance tap. 6 unplugs, 12 plug-ins every day. So much room for error but I labeled all my connectors (ie 1 -> 1 .... 2 -> 2...) which I believe saved me from human error at least a couple of times.

Sorry I should have stated, I'm using Adaptto controller with integrated BMS. One of the many features is the ability to take virtually any DC power source with voltage below the pack voltage and step it up to bulk charge. Cells are monitored by the BMS and the charging can be controlled according to cell voltage. If one cell hits 4.2v (reconfigurable to whatever you want) the charger power is reduced or stopped entirely. Desired charge voltage, charge power etc is all adjustable via onboard screen/interface.

This means you can use a cheap, light, super reliable power supply that's not necessarily a battery charger and charge quickly and accurately. I have a few different power supplies I have used that cost varying amounts, my current preference is a front end rectifier that delivers 52v, 1800w. Charging at 1800w is awesome My previous power source was a pair of 600w server power supplies connected in series for 1200w @ 24v. I ran this at an easy 1kw charge rate. Cost me nothing as I had the power supplies lying around but these are available on ebay for $20-$50 pretty regularly.

I basically never need to open my battery compartment any more and cells are kept within 10mv.