20s Charging Using Two Balance Chargers

Hi all, I haven't been on this site for years, my old username was "mechanix" but I don't know what email I used to register originally so I was unable to recover my password. I never really posted too much, but learned a lot from everyone. It's refreshing to see a lot of familiar faces as I'm looking around after all these years.

I started a build close to 5 years ago that I never really fully finished:

https://endless-sphere.com/forums/viewtopic.php?f=3&t=85838



It's been sitting in my garage ever since and I'm trying to figure out the best way to charge this beast to finish this project once and for all. I have two iCharger 1010B+ balancing chargers and some power supplies. The power supplies will have a common ground (using ATX power supplies with grounded plugs). There is continuity between the DC- and earth ground, so I thought to maybe just remove the ground plug on both the power supplies and not use this around water, etc. but I don't know if this would truly isolate the chargers. I have found two threads that talk about a similar problem:

https://endless-sphere.com/forums/viewtopic.php?t=20939

https://endless-sphere.com/forums/viewtopic.php?f=14&t=71464&start=25

Here is a picture of the wiring diagram I have currently, I am thinking about just removing the ground plug for the chargers, but am not sure if that will be enough to truly isolate the chargers so one isn't seeing 40V more that it is expecting:

Separate the sub packs and charge separately

That was my first thought, but the pack is completely sealed and would be tons of work to open them back up. There has to be a way to charge 20s...is the best practice now to use a BMS?

One option would be to charge 10s at a time, but there has to be another solution???

Another option would be to sell the iChargers and pick up a BMS/bulk charger which I'd rather not do since I already have all the material I need in theory.

You trying to charge with 2 36V chargers or you trying to get twice the amps charging?

Maybe get a dedicated balancer with a decent current rate, just use when needed.

Do put cell-level voltage monitoring in, a "smart" BMS with BT will do

but just charge at pack voltage only.

Thanks for all the replies so far - all valid options. I would like the simplicity of just plugging a charger in and pressing "go". Is there an easy way to isolate these chargers? In searching around, I have found a couple options. I'm no electrical engineer but I think I either need a "120VAC to 120VAC isolation transformer" or a "120VAC to 36VDC isolated power supply" or ????

Lots safer and easier to break up the pack.

Really once you get past 12S or maybe 14S

easiest otherwise is to bulk charge just the power pair.

A good BMS can in theory handle both the HVC based at cell level, and the balancing process, but they cost the Earth.

So to save money, at least get the ability to **monitor** the cell level voltages, and you can manually make sure you don't let any groups go too high.

Once you know what that pack level voltage is, adjust it down and you should be fine for at least a while, just check on it regularly

and then deal with re- balancing as a maintenance routine

My apologies, I guess I wasn't too clear on what my question was (and the questions keep on mounting!)

I do plan on bulk charging to around 90% or so, but maybe once a month, or if I want to charge to 100% before a long trip I would like to balance charge it. Taking the pack apart is not an option, so I am left with the wires coming out of the battery enclosure as shown on the wiring diagram above.

Question 1:
Do power supplies exist that would properly isolate the chargers such that they could be hooked up like in the diagram above? I have some laptop chargers that do not have ground plugs and have no continuity between the primary and secondary and a "hi-pot ok" power supply (Advantech P1G-6300P)

Question 2:
If the above power supplies do isolate the chargers, are there still safety issues? what are the safety issues?

Question 3:
If the only possible way to do this is with a BMS, are there any good options? I'm not opposed to spending money if it means doing this right.

Thanks!

apparently Meanwell HLG series are isolated, and can be series'd as well as paralleled

But that's above my paygrade, I'd go for the BMS approach if the pack can't be split

As to the rest, I'll let others step in

What you're proposing is fine as long as you use appropriate power supplies. Look for with the two concentric squares which means double insulated, which gives 3kV of isolation.

So
Q1: it's fine, most laptop chargers are double insulated but some are grounded so take care and measure the impedance. No idea what your hipot thing is... If it's hipot able it should be fine. Check the resistance to earth. Make sure the balancer can handle whatever voltage you give it
Q2: your remaining safety issues only arise of you cross your wiring plus the standard risks of 80V and lithium
Q3: you could do this with a BMS. I'm on my fourth BMS following the others failing so I'm not convinced this is the best option.

If you split the packs and give each it's own BMS, you have serious BMS issues... The MOSFETs are only rated to break the voltage from one of the packs and will go up in flames trying to break the series voltage of 2. Definitely don't do that.

Yes, one easily removable BMS for the whole pack.

When sub-packs separated, no BMS needed, the balancing charger is in control

Teknishun said:

Taking the pack apart is not an option, so I am left with the wires coming out of the battery enclosure as shown on the wiring diagram above.

Click to expand...

Have you already measured all twenty p-group voltages with your DMM to determine if any of the p-groups are too far out of whack (too low or no voltage)? You may end up having to disassemble part of the pack if one or more p-groups need to be repaired/replaced. If that is the case you may want to consider splitting the pack and making up Y cables for both the two 10S balance leads and Deans charge connectors so you can keep an eye on all 20 p-group voltages during bulk charging. You'll need to use a 10awg silicone allowing you to split the pack and only need to use one 1010B+ with Y cables to charge both split 10S packs at same time.

If you don't first disconnect the 10awg silicome cable linking the two 10S split packs into the 20S pack you will see and hear sparks, but it only lasts a split second as the JST connector is quickly fried on the Y connection. I've done it a couple times over two years. Then need to get out my soldering iron, solder and new connector with leads to connect to the existing leads. After a couple times learning the hard way you hopefully tend to remember not to do it again.

Anyway first connect two 10S JST female connectors to the loose ends of the existing 20S lead wires. Then write down each p-group voltage when taking individual readings with your DMM in the first photo. Then onto bottom balancing (or mid-balancing if in storage for several months) of most all 20 p-groups to establish a middle-of-the-road happy medium.

Bottom balance by using a combination of discharge balancing and/or charge balancing (1S setting on your iCharger 1010B+) as shown in the following two photos to bring p-groups to within at least 25-30mV of each other the first time around. You may need to get a DMM that reads three decimal places so you can balance the p-groups within 25-30mV of each other. Bottom balancing can be time consuming with 20 p-groups that may need some degree of balancing after every other discharge cycle. Hopefully not after every discharge cycle unless you've got the time and it's necessary. A happy medium in the least amount of time may require both discharge and charge bottom balancing to bring all 20 p-groups within as least 0.01V of each other if you don't have a DMM that reads to three decimal places (mV).

Needs to be done meticulously the first time around if battery has been in storage for some length of time to bring p-groups within at least 25-30mV of each other. Then after that you may only need to occasionally bottom balance.

If you expect your 20S BMS to balance your pack you'll need to consider getting an "active" balancer.

In the third photo you can see that i left the other pins on as it helps to secure the JST male connector into the female JST connector as you charge one p-group at a time. P-group voltage that needs to be increased to bring it in line with the middle-of-the-road p-group voltage needed when bottom balancing before bulk charging p-group cells to 4.10V. That's 90% figuring a Controller cut-off discharge of 3.20V per cell/p-group.

You may only need to bottom balance every other charge/discharge cycle as long as the 20 p-group variances aren't off by more than 0.01V before bulk charging. Check each individual p-group voltage before (bottom balancing) and after charging so p-group voltages don't vary by more than 0.01V from one another. The third photo is the tehnique i use with my balance charger set on 1S, only 1.0A (im retired so in no hurry) and keep track of time. It takes me at my settngs about 10 minutes if a low variance needs to be increased by as much as 0.04V due to unacceptable self-discharge with one of the 30Q p-groups. After a while you'll get a feeling for how long it takes at a given amperage to increase the voltage from say 3.50V to 3.53V If the happy medium you're balancing all 20 p-groups happens to be 3.53V. Hope this helps ...

eMark - Thanks for the thorough reply! Fortunately my cells are all in series, no parallel - they are Nissan Leaf cells. I will definitely keep all that knowledge in mind if I ever build a pack with cells in parallel.

john61ct - I love the idea of a BMS, but can't find any that seem to be good options that I feel good about their quality. Balance charger it is!

mxlemming - I just so happen to have a bunch of Lenovo laptop chargers that have the concentric square symbols on them! I will give it a shot and we'll see what happens!

Of course, I will post pictures of any successes or failures I have.