Circuit breakers/ battery overcurrent protection

[cerewa]

I bought a battery from Yesa with a current rating of 1C = 10A = about 240W. Their website says it is suitable for 350W motors.

I was thinking about how to come up with a cheap and easy way to know how much current my motor was drawing or to avoid going over about 15A.

I popped over to ebay. At the moment if you search ebay for DC circuit breaker and then scroll down, you'll see

195 items found for dc circuit breaker in eBay Stores

including choices in sizes from 5-amps up to at least 150 amps.

One of them was 15amps and was for sale for about $11 US, shipping included.

I'm not sure I want to spend the $11, since my battery BMS apparently has a 20A limit built in.

I'm really not sure whether my battery would last much longer if it were limited to 10A or 15A instead of 20A and I really know nothing of the chemical processes of damage to LiPO4 batteries from overcurrent, overdischarge, and all of the other things that mean my battery will not still be going strong in 50 years.

So, does anybody have insights about how different battery chemistries are damaged (or not) by excessive current, or the different devices available to prevent excessive current either as a way to protect your battery or the stuff you have wired to your battery?

As a side note, with cells like A123's being able to handle 40 amps, or 100amps, or whatever it is [and some multiple thereof when you run packs in parallel] what is the deal with wiring for those things? Seems like you'd need wire as fat as a AA cell in order to handle the current and any kind of short could cause an explosion not in the cells (lithium-iron being a safe chemistry and all) but in any random item being subjected to such a ridiculous number of amps.

 

[Beagle123]

One of the disadvantages of faster discharge rates is that your battery actually loses capacity. So if you discharge at 3C instead of 1C you'll be losing a percentage of the overall energy.

I saw a chart for some lithium batteries where the capacity dropped very significantly (maybe 25%) with the big discharge rates. I imagine the effect is much less at 3C or so.

 

[flip_normal]

Excessive heat kills batteries. Like any chemical reaction heat will cause it to go faster. Some EVers use battery warmers to get more out of the battery, especially old ones, but too much heat is definitely not good.

Heat in the batteries is caused by their internal resistance. The high C rated LiFePO4 batteries have a very low internal resistance (~30mOhm) so they can discharge a lot of current without warming up much. You only need fat wires on a battery pack if the equipment connected to it draws a lot of current from the pack. Smaller motors won't pull many amps.

I've got one of these DZ47-63 C32 circuit breakers on my moped but I'm not sure how good it is since it didn't even trip when the controller shorted out. The cheapest way to prevent more than 15A continuous from being drained from the pack is to use a fuse in line with the battery wires. Don't forget to carry a spare or two though.

 

[fechter]

It's always good to have a fuse or a circuit breaker on the battery to prevent your wiring from burning up in the event of an accidental short.
To limit your current while riding, though, you really need to make the controller limit the current.
It's possible to tweak the current limit on most controllers, or you could use an external circuit like the one built into the CycleAnalyst to limit the current.

 

[marty]

It's always good to have a fuse or a circuit breaker on the battery to prevent your wiring from burning up in the event of an accidental short.
To limit your current while riding, though, you really need to make the controller limit the current.
It's possible to tweak the current limit on most controllers, or you could use an external circuit like the one built into the CycleAnalyst to limit the current.

Fechter - Thanks for giving what I think is the CORRECT answer to Cerewa's question.

Will go a little farther - Fuse should go on the positive side [usually RED] and close to the battery. Think one time use [throw away when they blow] are cheaper and more common then circuit breakers on electric bicycles? Here are some pictures.

Auto Parts stores sell in line holders.
Cerewa, your next question should be what AMP rating fuse should I use?

 

[ngocthach1130]

i asked this before but why don't we use household fuse to for amperage protection. They come in adequate amp we use. 20, 35, 45. Plus these day they have breaker fuse that's resettable. Only downside i see might be how fast they respond. They're rated for 120v so not sure how fast it'll be before they pop. I think it's great because we won't have to worry about spare fuse or worry about limping home after your only fuse blown.

 

[Jay64]

I was in the autoparts store the other day looking at their fuses and fuse holders. The fuse holder stated that it was rated for 32v. Are there any that can handle 36v?

 

[fechter]

The 32v rated fuses are probably good up to about 60v.

Above that, you run the risk of drawing an arc across the blown fuse like an arc welder. That could be ugly.

I've used automotive style self-resetting circuit breakers on my scooter. They seem to work fine, but I don't remember ever having a short to test if it will open properly. They are available up to 40 amps. I put two 30 amp ones in parallel on my Zappy, which runs up to about 60 amps.

 

[Beagle123]

I'm using a "mega amp" 175 amp solid state fuse. I thought those typical automitive fuses would have higher resistance because they have a little filiment in them like a light bulb. The only protection I'd want is for a short circuit. I bought it at autozone.

 

[EMF]

I'm using a "mega amp" 175 amp solid state fuse.[/size]

Never heard of those. What does it mean when it's solid state? Can you re-set it or something? Or does it simply use fancy electronics to permanently break the circuit instead of a filament of some sort.

 

[Rassy]

I installed the two prong 40 amp automotive fuses with heavy duty inline holders between each 48V string and the common stud for all strings, positive side only. When accidently shorted, the fuse popped with no damage to any wires, etc.

Currently I have two strings of SLA, 24AH total, that run two controllers (one for each motor) that operate from the common studs the battery strings are attached to. For the last week or two the trike seemed a little sluggish, and I was thinking the cooler weather was taking its toll on the SLA. Then, two days ago I popped a fuse coming up the hill at full throttle. I also have a breaker between each stud and controller that I use as a main on/off switch. I don't know their ratings, they came from WE with the kits, are made in England, and have no ratings on them. Anyway, when the trike stopped, I turned off the breakers, found and replaced the blown fuse, thought it was strange only one fuse blew, so figured maybe one breaker had tripped and I didn't notice. Next day the same thing happened, and I noted the breaker did not trip. Turned out a battery connection had come loose, so I was trying to pull 70 amps from one 12AH string, through a 40 amp fuse. So these 40 amp fuses are sort of a slow blow somewhere between 40 and 70 amps.

 

[Beagle123]

Never heard of those. What does it mean when it's solid state? Can you re-set it or something?

No, I just used the term "solid state" to say its sealed with no moving parts. When it blows, its garbage.

 

[marty]

i asked this before but why don't we use household fuse to for amperage protection. They come in adequate amp we use. 20, 35, 45. Plus these day they have breaker fuse that's resettable. Only downside i see might be how fast they respond. They're rated for 120v so not sure how fast it'll be before they pop. I think it's great because we won't have to worry about spare fuse or worry about limping home after your only fuse blown.

Sure you can use household fuse on a bicycle. Could also use bicycle fuse in house. [Note from our legal team - Follow all codes and hire a licensed electrician] Fuses used in a building are usually larger then fuses in a motorized vehicle. There are more fuses then what you see at Home Depot. 6,202 fuses at http://www.newark.com

I'm using a "mega amp" 175 amp solid state fuse.

Wo! isn't that a bit high amps? If amps are to high? Your scooter could catch on fire and burn your butt Recommend you check with Fechter for suggestions on what amp fuse or circuit breaker to use?

 

[Beagle123]

Wo! isn't that a bit high amps? If amps are to high? Your scooter could catch on fire and burn your butt

I've already thought of that, and I have a plan--sit down.