How to protect a LiPo battery from short circuits

[aangel]

My brand new LiPo battery stopped working last night after perhaps 6 hours of operation. Though I don't recall short circuiting it (a big no-no prominently printed on the side of the battery) and I didn't see a spark, it's possible that I did as I had several wires exposed.

Now, the voltage I was measuring from the battery was fluctuating wildly beforehand and when I spoke to tech support at ExpertPower this morning he suggested that, given the fluctuating voltage and that the battery died so soon, it was likely a problem with the BMS and that I should return it. Amazon is on the case doing that now.

However, it does seem to me I was careless with the battery given that perhaps a BMS can get fried relatively easily. I'm not used to working with Lithium batteries and it seems likely that they are more fragile (due to them having electronics in the form of the BMS). My past experiences quickly crossing wires with lead acid provided a spark but the battery kept working.

So here is my question: presuming that I will take care to protect the next battery from short circuits, what are some of the fuses/breakers/magic setups that I should consider?

Other details:
• battery: 20amp•hr from ExpertPower https://www.amazon.com/gp/product/B07X523S96
• will go through this control panel after the fuse/breaker: https://www.amazon.com/gp/product/B08MQHBPBF
• expected load: perhaps just a few amps? Needs to run some LED lights and provide power to the plugs in the panel, above
• location: in a trailer likely to get really hot when traveling through the South
• it seems I want a really quick breaker or fuse to protect the BMS but this is new territory for me so I would love to hear people's thoughts!

Cheers,
André

 

[Hedges]

We expect to at least see a spark if you short it. BMS FETs might be toast, but you ought to get a spark.

With cell resistance spec of 0.25 milli-ohm and measured around 0.17 milli-ohm, I calculate 20,000A short circuit current.
Maybe it is really less, but haven't seen a spec or meaurement.

A class T fuse has 20kA AIC, so that's what we recommend.

I was thinking of 280 Ah or 100 Ah cells, your battery is 20 Ah so could be much lower short circuit current. If you can find a value for short-circuit current or cell resistance you may be able to select an adequate but cheaper fuse.

There are even faster "semiconductor" fuses which might be better at protecting the FETs and not just the cables.

Ferraz Shawmut / Mersen Sales | A50QS Series / 500V

A50QS Amp-trap Form 101 fuses grew out of the need to improve the overall performance of semiconductor fuses in response to new equipment requirements. The A50QS encompasses the best protection features lower I2t to provide better protection for equipment, longer life when subjected to cyclic...

ferrazshawmutsales.com

But considering prices are around half what your battery costs, may not be the route you want to go.

 

[aangel]

Thanks, @Hedges .

I was hoping I could use something like this because I could screw it into my mounting board (although I see now the back isn't very friendly for what I want to do):

https://www.amazon.com/wohhom-Circuit-Breaker-Waterproof-Inverter/dp/B08HLJ2G8Y

But I don't have a sense of whether that would break quickly enough. I certainly can't see myself using 20A very often.

 

[aangel]

This is better because the terminals are on top:

https://www.amazon.com/Circuit-Breaker-Waterproof-Trolling-Resettable/dp/B089M6NGZ6

 

[Hedges]

Likely those breakers are (&@? and won't carry the load.
Blue Sea is one source for quality breakers of that style.
Quality fuses are the most sure thing.
If you can find what the short-circuit capability of that small battery is, maybe an economical MRBF fuse right on the battery terminal would be ideal.

 

[Just John]

My brand new LiPo battery stopped working last night after perhaps 6 hours of operation. Though I don't recall short circuiting it (a big no-no prominently printed on the side of the battery) and I didn't see a spark, it's possible that I did as I had several wires exposed.

Now, the voltage I was measuring from the battery was fluctuating wildly beforehand and when I spoke to tech support at ExpertPower this morning he suggested that, given the fluctuating voltage and that the battery died so soon, it was likely a problem with the BMS and that I should return it. Amazon is on the case doing that now.

However, it does seem to me I was careless with the battery given that perhaps a BMS can get fried relatively easily. I'm not used to working with Lithium batteries and it seems likely that they are more fragile (due to them having electronics in the form of the BMS). My past experiences quickly crossing wires with lead acid provided a spark but the battery kept working.

So here is my question: presuming that I will take care to protect the next battery from short circuits, what are some of the fuses/breakers/magic setups that I should consider?

Other details:
• battery: 20amp•hr from ExpertPower https://www.amazon.com/gp/product/B07X523S96
• will go through this control panel after the fuse/breaker: https://www.amazon.com/gp/product/B08MQHBPBF
• expected load: perhaps just a few amps? Needs to run some LED lights and provide power to the plugs in the panel, above
• location: in a trailer likely to get really hot when traveling through the South
• it seems I want a really quick breaker or fuse to protect the BMS but this is new territory for me so I would love to hear people's thoughts!

Cheers,
André

You might want to check some products here:

Batteries & Chargers | Powerwerx

Rechargeable AGM batteries, smart multi-stage battery chargers, computerized battery analyzers 7 more. All available from Powerwerx, shop online today!

powerwerx.com

As a rule, hams know what they are doing.

 

[Just John]

This is better because the terminals are on top:

https://www.amazon.com/Circuit-Breaker-Waterproof-Trolling-Resettable/dp/B089M6NGZ6

Like Hedges said, cheap Chinese circuit breakers are generally dangerous, don't cheap out there.

I seriously doubt that you caused any problem with your battery, you would notice if you shorted it (trust me), and unless it is garbage, a BMS isn't that fragile.

 

[Just John]

This is better because the terminals are on top:

https://www.amazon.com/Circuit-Breaker-Waterproof-Trolling-Resettable/dp/B089M6NGZ6

Much better:

https://smile.amazon.com/Blue-Sea-Systems-Circuit-Breakers/dp/B005BI50RY/

Cheaper option:

Eaton Bussmann 285 Series Resettable Circuit Breakers Surface Mount up to 150A

These high-amp, Type III circuit breakers are typically used in automotive auxiliary and accessory circuits for trucks, buses, RVs and marine applications. High-amp circuit breakers also have applications in battery charger systems and DC audio systems.

powerwerx.com

 

[aangel]

@Hedges: a fuse right on the terminal would be great, would save a bit of space.

@Just John: I hadn't realized I had specified a cheap Chinese one; agreed that the others are better quality. And thanks for turning me onto PowerWerx.com.