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Old 02-20-2018, 10:04 PM   #21
Sergio
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Default Re: Onboard Charger Killswitch

Did you bottom balance the cells or are you using a BMS?
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Old 02-20-2018, 10:13 PM   #22
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Default Re: Onboard Charger Killswitch

No and no

I think the guy who put it all together did the bottom balance though.

Do you know of a easy to use BMS?


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Old 02-20-2018, 10:33 PM   #23
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Default Re: Onboard Charger Killswitch

No I don't, but a few members on this site have different BMS systems with their Nissan Leaf modules, from simple to more robust, perhaps one of them will see this thread and post their comments.

You really cannot depend on voltage readings for lithium, they go down pretty fast near the end of the SOC curve.

When using bottom balance (bringing all the cell voltages to the same "empty" SOC), you use an amp-hour meter to measure the AH charged and discharged to keep the individual cells from overcharging or discharging.

You may know all this but just a reminder for other folks that may read the thread and assume they can just connect these high-energy cells without some safety measures.
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Old 02-20-2018, 11:20 PM   #24
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Default Re: Onboard Charger Killswitch

I have a 120v relay on the power wire to the solenoid so when the charger is plugged in the solenoid is disconnected. Easier than trying to disable the key. Charger is wired directly to the pack.


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Old 02-21-2018, 09:28 AM   #25
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Default Re: Onboard Charger Killswitch

Eliminate parasitic draw? The relay is wired in a fashion that it has to be activated (powered on) during charge! The relay IS the parasitic draw you seek to eliminate!
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Old 02-21-2018, 10:13 AM   #26
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Default Re: Onboard Charger Killswitch

Quote:
Originally Posted by cgtech View Post
Eliminate parasitic draw? The relay is wired in a fashion that it has to be activated (powered on) during charge! The relay IS the parasitic draw you seek to eliminate!
With the 120vAC relay the 0.04 amp load would be on the house power.

I would be more concerned with how to monitor the individual modules/cells.

Rwalsh77, You should at least take voltage readings from each individual "cell pair" inside each module.

Since the "middle" taps are not connected together, you can get the voltage reading of each "cell pair" (there 2 pairs inside each module) by measuring between the center tap and each outside tap.

Make sure they are very close in voltage so You don't damage the cells by over-discharging them.





Edit:

I just saw a picture of your setup below, You do have the center taps connected, so in fact you have a: 5S(2S4P) lithium cell setup.
http://www.buggiesgonewild.com/elect...ml#post1474278

Last edited by Sergio; 02-21-2018 at 10:42 AM.. Reason: Comment about the cell arrangement
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Old 02-21-2018, 04:07 PM   #27
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Default Re: Onboard Charger Killswitch

Looks like my lithium took over this post but I like it. I’m always up for learning more.

As for balancing. I occasionally take the readings you describe and the largest gap in voltage I ever saw was .02v

I’m interested in a BMS though if you want to point me in the right direction.

I think I should post a better picture of the terminals too. I can get the “half pack” voltage to read and I’m pretty positive it is a 10s2p set up


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Old 02-21-2018, 04:10 PM   #28
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Default Onboard Charger Killswitch



I could be wrong, it’s happened before, but this looks like each 2 are in parallel making 5 sets and then those 5 sets are in series. Note that not all the red terminals are on top/bottom row, each set of two alternate.

Also, took voltage readings just now and they were all reading 4.03 or 4.04. Full pack is 40.3


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Old 02-21-2018, 05:16 PM   #29
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Default Re: Onboard Charger Killswitch

You always put the number of cell "groups" in Series first, followed by How many cells are in parallel in each group.

If You look at the picture I posted, each nissan leaf module is a 2S2P cell arrangement.

When You place the modules in parallel with the center taps connected, You get 2S4P cells (just draw it out).

You then string 5 of those combos in series so in modules You get: 5S2P, but I tried to represent it cells for you as 5S(2S4P)

Some folks run their lithium setup without a BMS, but in that case is safer if you use an AH meter to measure discharge rather than pack voltage reading.

The main reason You never see a setup in a commercial environment without a BMS is that a single cell failure (due to any reason) could lead to a catastrophic event during charge or discharge.

There are many BMS systems out there, the cheap ones are not any better than having none if you monitor the voltages.
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Old 02-21-2018, 05:28 PM   #30
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Default Re: Onboard Charger Killswitch

From my experience with the leaf pack so far I have not seen my cells have more than a .02-.03 voltage difference. Granted I do have a BMS but it only balances when on charge and individual cell voltages exceed 4.10v. At the rate I use my cart I only charge it once a week. Maybe I’ll plug it in for 30-45 min mid week for insurance if I’m going further than the usual 4-5 mile round trip and when that happens it is not getting balanced. I’m not always nice on the pack either, im enjoying ludicrous mode with the Executioner. With that said, I think these packs are fairly stable and if monitored properly throughout the pack life a BMS might not be absolutely necessary. However, I prefer the zero maintenance aspect so for me a BMS is needed to support my laziness. BUT, if you are willing to periodically check individual cell voltages and balance them manually when necessary I wouldn’t imagine your pack would have a shorter lifespan as a result.

One key point is not to run them dead and there is no real benefit to charge to a max 100%. The last 3-4% of charge is a diminishing return. So as long as you are always within say 3.1v to 4.15v per cell, the pack should be a happy camper for a long time. Other cell brands and types might be different, but from the 50-60 hours I’ve spend researching and understanding the Leaf cells, that’s my conclusion.

I’m also not an electrical engineer so please don’t take my opinion as gospel. Frankly PingEye3 is probably the most informed person on BGW when it comes to Leaf cells.


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