Requesting a BMS recommendation after fire: 8S LiPo

Batteries, Chargers, and Battery Management Systems.
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fossilfool   100 µW

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Requesting a BMS recommendation after fire: 8S LiPo

Post by fossilfool » May 16 2020 3:02pm

Hello,

Long time reader, first time poster. I come seeking a BMS recommendation for my Choprical Chopper and other projects. The chopper looked like this in its hay day. Now it's a charred but recoverable mess after a battery fire.

Image

I have been using Hobby King LiPo "Multi Star 12000 mAH 8S 29.6V batteries with a 2C discharge rating. These were being sold cheaply by Hobby King a few years ago and I stocked up. I was aware that LiPo pouch batteries can catch fire while charging. I went through a process of trying 2 different safety methods: BMS and small voltage alarm.

The BMSs didn't work reliably!

I have 6 packs in my chopper in a series parallel arrangement: 3 series levels of 2 packs each. Within a pack of 2, what would happen is that one of the BMSs would shut off, causing the other pack in that pair to do twice the work. To my memory this happened repeatedly with packs that weren't out of balance. I would check with the voltmeter on the small connector periodically and after an incident like this. I stopped using BMSs.

The alarms went off way lower than what I deemed safe. Even though the alarm voltage was settable, I wasn't getting good results. I later found out that all the alarms (I bought one for each pack) were made wrong and cell 7 and 8 were measuring way wrong as confirmed by my voltmeter.

I stopped using the alarms.

I tried to ensure safety with frequent voltmeter checks. Then recently I made a mistake in following my own protocols and overcharged a weak pack and nearly caught fire to my shop! I was able to drag the bike outside but as as soon I did the fireball got too intense for me, so I yelled fire and got some backup from my employees. The powder fire extinguishers were not that effective. What really worked was a garden hose aiming steadily at the pack. Then when it was less energetic but still smoking I removed it from the bike with thick leather gloves and dunked it in a bucket. If this had happened on a weekend, I would have had to do it all by myself and I'm not sure I would have had the presence. So I'm very grateful that we put it out together, and that no one was hurt, that we didn't lose our building, and that the bike wasn't even all that damaged. What looked like a huge fireball was happening mostly above the bike, and there wasn't as much damage as I feared.

Now I plan to rebuild the Choprical Chopper and I plan to do other electric bike projects. The energy density of these LiPo packs, and the fact that I already have them, make me want to use them but certainly with a BMS, and hopefully with my custom fiberglass saddle designed differently so that I can remove the battery easily and charge it in the middle of an open space.

Experienced builders: I seek your advice. What BMS do you trust? This bike peaks out at 3000W so each pack is being asked to do 500W or 16A. As mentioned above they are rated at 2C which would mean up to 24A. So I am running the packs within their rating.

Thank you, Paul
Last edited by fossilfool on May 16 2020 4:38pm, edited 1 time in total.

999zip999   100 GW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by 999zip999 » May 16 2020 4:15pm

Paul sorry for your lost it's very emotional and hollow feeling that such box of plastic and be so volatile. Keep your head up brother

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Sunder   100 MW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by Sunder » May 16 2020 8:08pm

fossilfool wrote:
May 16 2020 3:02pm
Experienced builders: I seek your advice. What BMS do you trust?
None. I don't trust any BMS. That's a bit tongue in cheek, but also true. I've had two BMSes fail, both from BMS Battery admittedly, so at the very least, I'd say avoid them.

First one left a balancing circuit open, and puffed the pack from over discharge.

Second, I don't know the mode of failure, but the pack caught in fire during charging. Luckily it was outside away from anything flammable, and a neighbour saw it before any serious damage. That was a Multistar as well, so I am wondering if those were perhaps manufactured to too low a spec and why it's no longer available.

I now use the ANT BMS with the voltage display. I check regularly for any unusual deviations that aren't enough to trigger the BMS. My intent is that if any cells have any significant deviation from it's peer in any meaningful way, I'll either cut it out, or replace the whole pack. But since I have shifted to more expensive packs, I have not had any issues.

A BMS is only one of many "controls" as a risk manager would put it. Regular electronic, visual and even olfactory inspection is required. (If you can smell the sweet ester smell in a pack, something is wrong)
eBike: Q100H on 16S with Phaserunner FOC Controller
eMotorscooter: Vectrix VX-1 Died... Electrified Ninja in Progress!
eCar: Mitsubishi Outlander PHEV... Warramty expired. Still not game!
eHouse: 6.2kw On-grid solar with battery backup coming soon!

After 5 builds, the best advice I can give, is start with high quality products. I prefer http://www.ebikes.ca

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by jonyjoe303 » May 16 2020 10:55pm

I would look at the chargery bms8(cost about 95 dollars), its what I use on my 4s solar system, I trust it more then any of the cheap bms.

It uses contactors/relays to stop the charge/discharge, you would need 2 contactors one for charging and one for discharging. I use a small 4 dollar 30 amp automotive relay on my system. In your system for the discharge you need a high amp contactor that can handle the current you will use, the only limit for amps it can handle is the size of your contactor.

It has audio/visual alarms and an lcd screen to check cell voltage. I used the one on my system for the past year 24/7 and been very reliable. I also have an overvoltage protection relay, that will also stop the charge if the bms fails, I don't trust the bms by itself also when charging. Overvoltage protection relay is only 6 dollars, very cheap price to pay to keep safe.
chargery bms8t.jpg
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fossilfool   100 µW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by fossilfool » May 17 2020 12:21am

Thanks for your recommendation. Would I have to get one of these for each of the 6 packs in my series / parallel configuration?

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by jonyjoe303 » May 17 2020 9:51am

One would only work during charging if the 3x packs were connected in parallel.

If you plan on keeping your 3 packs in series during charging/discharging, what you actually need is a 24s bms, that would actually work better and also prevent one bms from activating before the others. You can find some smart bluetooth 24s bms also in the 100 dollar range but I never used any to recommend one.

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motomech   1 GW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by motomech » May 17 2020 10:48am

It really takes some work to catch 10C or 12C MultiStar on fire:)
I've been telling folks to not use a BMS on LiPoly for years, but nobody believed me.
Here are some of my posts;

viewtopic.php?f=14&t=105666&p=1546453&h ... l#p1546453


viewtopic.php?f=14&t=102476&p=1499326&h ... an+well#p1

viewtopic.php?f=3&t=98295&p=1439787&hil ... l#p1439787

viewtopic.php?f=14&t=94742&p=1388446&hi ... well#p1388

viewtopic.php?f=14&t=91919&p=1340753&hi ... l#p1340753

viewtopic.php?f=14&t=91438&p=1333365&hi ... l#p1333365

And that's only a few.

In my 9th year using LiPoly and all the time refining the process to where I'm now down to almost a "plug and play" system.

The "keys" are;
Use big bricks and don't configures more than 2P so the string doesn't need to be broken to charge.
Use a Mean Well HLG to bulk charge.
Ck. and balance w/ Battery Medics.
Observe the 80% D of D rule.
Carry enough capacity that one doesn't really need to charge over 4.10 V (that's easier on connectors too, little pre-spark)
Motomech


'07 GT Idive 4 4.0, Q100H 201 frt. mounted, 14S Multistar LiPoly, elifebike 9-FET 20A controller. Mean Well HLG-320H-54A, Crazy Bobs on Alex DM32's 21 to 22 MPH. viewtopic.php?f=3&t=28151&p=1373714&hilit=Idrive#p13737

john61ct   100 GW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by john61ct » May 17 2020 12:15pm

A good quality BMS can cost many hundreds, but I would not really trust any of them alone.

Wire them so they are removable, easily replaced.

Add a completely separate thermal sensor system tied into a master pack cutoff contactor for redundancy.

For charging, get at least one quality and powerful 8s balancing charger

Top brands are:
Graupner, FMA/Revolectrix (CellPro), Hitec , iCharger (Junsi), ISDT, Hyperion.

Some can do multiple packs at once

do not parallel charge unless you use the safety boards where every cell connector is fused.

And ideally, add a completely separate HVC [s]in case[/s] for when the main charge regulator fails.

Do not walk away while a charger is active, best to watch them like a hawk.

Be grateful you didn't burn your whole house down!


fossilfool   100 µW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by fossilfool » May 17 2020 3:21pm

motomech wrote:
May 17 2020 10:48am
It really takes some work to catch 10C or 12C MultiStar on fire:)
I've been telling folks to not use a BMS on LiPoly for years, but nobody believed me.
Momotech, thanks for replying. I did read your other posts. I like the process and I could see approaching it this way, thx.

If you don't use a BMS, how do you ensure that you don't overdischarge? I use the Cycle Analyst and I have settings programmed into it. Do you do the same? Can you share your settings plz? Like how low per cell do you allow your battery to go? Thx.

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motomech   1 GW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by motomech » May 17 2020 6:05pm

double post
Last edited by motomech on May 17 2020 6:37pm, edited 4 times in total.
Motomech


'07 GT Idive 4 4.0, Q100H 201 frt. mounted, 14S Multistar LiPoly, elifebike 9-FET 20A controller. Mean Well HLG-320H-54A, Crazy Bobs on Alex DM32's 21 to 22 MPH. viewtopic.php?f=3&t=28151&p=1373714&hilit=Idrive#p13737

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motomech   1 GW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by motomech » May 17 2020 6:09pm

again, for some reason I can't delete
Last edited by motomech on May 17 2020 6:38pm, edited 1 time in total.
Motomech


'07 GT Idive 4 4.0, Q100H 201 frt. mounted, 14S Multistar LiPoly, elifebike 9-FET 20A controller. Mean Well HLG-320H-54A, Crazy Bobs on Alex DM32's 21 to 22 MPH. viewtopic.php?f=3&t=28151&p=1373714&hilit=Idrive#p13737

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motomech   1 GW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by motomech » May 17 2020 6:24pm

How not to over-discharge?
Well, nothing changes on the dis-charge end when you change up the charging method except you are getting rid of the unreliable BMS
Just calculate 3.65V times to number of cells and keep using the CA, but you should carry enough capacity that you don't go below 3.75 Cell. Your batt.s will get more service life that way.
And watch the Voltmeter, LiPoly dis-charges very much linear, so it makes a good "fuel Gauge".
Motomech


'07 GT Idive 4 4.0, Q100H 201 frt. mounted, 14S Multistar LiPoly, elifebike 9-FET 20A controller. Mean Well HLG-320H-54A, Crazy Bobs on Alex DM32's 21 to 22 MPH. viewtopic.php?f=3&t=28151&p=1373714&hilit=Idrive#p13737

fossilfool   100 µW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by fossilfool » May 17 2020 9:40pm

Motomech, thank you for your reply. If you let your cells charge up to 4.0 and you don't let them go below 3.75, aren't you only using like 30-50% of the battery's capacity?

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by john61ct » May 18 2020 1:42am

No the volts vs SoC curve for LiPo is drastically different from regular LI chemistries.

Up at the top 4.05 - 4.10 would add a bit more capacity, depending if CC only or holding Absorb a while

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by dogman dan » May 18 2020 6:20am

Well, here's what I learned after my bike burned down my garage, making the house uninhabitable for almost a year.

OUTSIDE. And not on the bike / vehicle. NO EXCEPTONS.

Otherwise, you were on the right track for safer use of lipo, you just picked some shitty lipo and then used it too long. Keep em fresh, like 2, 3 years max. Always undercharge if you bulk charge. Then if you do screw up and over charge a cell or two, that pack is toast. Same for an accidental over charge.

Your protocols are ok, but should have included retiring anything suspected of damage.

This did not happen out of the blue, betcha you had plenty of signs it was time to retire those cells. What I do to retired cells, is use them on my 24v lawnmower. They store separate from the other stuff, charge only to 4.1v, and if they go, they only take a wore out old mower with them. On the mower, I have had 5 year old, puffed up packs still run fine, at very low discharge rate. Even the cheap, 20c stuff. Don't buy that anymore, 30-40 c from now on.

fossilfool   100 µW

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by fossilfool » May 19 2020 12:22pm

john61ct wrote:
May 18 2020 1:42am
No the volts vs SoC curve for LiPo is drastically different from regular LI chemistries.

Up at the top 4.05 - 4.10 would add a bit more capacity, depending if CC only or holding Absorb a while
When you say that the lower voltage limit is 3.75 (which seems really conservative to me, but I'll take your opinion on it) is that under a load while climbing a hill or while the battery is sitting there?

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by fossilfool » May 19 2020 12:24pm

If a LiPo pack has a 2C rating, why does that make it cheap?

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by john61ct » May 19 2020 10:26pm

LiPo is used mostly for RC hobbies, model airplanes, drones

designed for absolute maximum power density, lowest possible weight, fire risks be damned.

As the chemistry science has advanced, all the R&D has been going into increasing C-rates.

2C is old and crappy, therefore cheap.

Packs that can actually hold say 35C continuously are the pricey hotness.

But less energy density.

So you only want to pay for the actual C-rate you need.

I don't mean the fraudulent claimed C-rate, but those actually tested and verified by expert forum members.

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by john61ct » May 19 2020 10:29pm


fossilfool wrote:When you say that the lower voltage limit is 3.75
Wut? not me!


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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by john61ct » May 19 2020 10:31pm

Read from here forward

viewtopic.php?p=1557126#p1557126

Completely different chemistry, so actual SoC vs Volts chart is radically different.

Plus good LiPo won't sag under load nearly so much.

But general principles are the same.

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by john61ct » May 19 2020 10:36pm

Many people are wealthy enough to not care about longevity, just buy a new pack every 100 or even 50 flights.

They can discharge to 80%DoD every time.

The rest of us try to get 2-300 cycles or even more.

High C-rates burn them up fast, but some use cases, sometimes just can't be avoided.

Leaving more capacity in the pack on average can help compensate, at the cost of long range.

If you want lower DoD and long range, have to carry lots more Ah, space and weight.

Balancing the priorities, up to you.

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by miro13car » May 20 2020 11:06am

BMS also called BatteryMurderingSystem.
I would never ever trust Ebay, China-type kind of BMS.
I myself simply do not use any BMS - dont see any use for any BMS on my pack.
cells stay balanced after thousands of kilometers ridden.
on charging I use celllog for HVC .
Eplus, Bionx

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by john61ct » May 20 2020 12:58pm

Pack level low-voltage protection

can be done without "a BMS".

Even if just an audible buzzer or flashing light

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by fossilfool » May 27 2020 1:42pm

john61ct wrote:
May 20 2020 12:58pm
Pack level low-voltage protection

can be done without "a BMS".

Even if just an audible buzzer or flashing light
John thx for your replies. The last audible alarm I purchased was weird. It was correct for cells 1-6 and incorrect for 7 and 8. Can you please recommend one you trust?

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Re: Requesting a BMS recommendation after fire: 8S LiPo

Post by john61ct » May 27 2020 2:19pm

Afraid I haven't found one that suits me yet myself.

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