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Why is this wire so hot?

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turtlepower

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Dec 21, 2021
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Hi
I'm running this 100 amp PowerMax PM3-100LK battery charger in my box truck. It's set to 14.6 and "staged charging". It charges 2 100ah lithum batteries. When it's plugged in this part I'm touching gets almost too hot to touch. Both sides of this amazon 150A circuit breaker get hot. The wires are less hot the further I follow the wire in either way. I bought a 2 pack of these breakers, so I tried a different one. I also added copper washers you can see in the photo hoping for a better connection.
Any ideas?
PXL_20240522_205242880.jpg
 
150A fuse breaker gets hot with 100A max charge! Should be 1/2 the rated temperature rise. If you can keep your finger on it, maybe is working as intended.

Those breakers are thermal trip (slow) only, no magnetic fast trip.
It is located near the AC/DC charger.

Is there an inverter?

Would be good to have fast protection for shorts near the battery(s). Class T fuse is good.
Two 12V LiFePO4 batteries in parallel, MRBF fuses with holders on each battery probably sufficient (10k AIC at 14V)

Fuse amperage rating should be well above operating current so it never trips, is just for shorts.
 
It is located near the AC/DC charger. -> yes, you can see it in the pic, it's a few inches away
Is there an inverter? -> yes but it's off and still the wire is hot
 
Sure, inverter isn't what's drawing current through that breaker, only AC/DC charger is in that circuit.

Inverter presumably a higher current draw. Except, 100A charger is pretty big. 2x 100Ah batteries, so you're charging at 0.5C.
That may be 100% of allowed current, probably better to dial way down unless you need a fast charge.

Don't think you require a disconnect at the charger, so a quality fuse and holder would be one option.

And a big enough fuse at the battery.
 
cranking an honest 100 amps through one of those breakers will cause some heat. I have an old, think 30 years+ phoenix gold audio breaker thats rated at 250 amps. it powers my compressor, and both sets of KC highlighters on my truck as well as my amps.

With all four lights on its about 40 amps draw. if I let the compressor run its 30 amps so a total of 70 amp draw and the bolts will get warm to the touch after a short period.
crank the orions up and jam really hard and it will get past the warm stage and into the lets not touch that again stage. not enough to trip anything as its no where near the rating, but it does it hot to the touch.

clean all contact surfaces, and coat with noalox or something similar then torque to spec for the size of the bolt. poor connections exacerbate heating issues.
 
"too hot to touch" isn't actually hot. It's generally 120F / 49C
That's not "hot" for majority of electronics. Even majority of plastics.

Be very careful with those breakers though, I wouldn't trust them, especially not on wood. I screw some hardie backer board on top of all the wood.
 
The wire size needs to meet two different requirements to work well:
- Ampacity
- Voltage drop ( due to losses )

Here is an ampacity chart:

www.cerrowire.com

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.
www.cerrowire.com www.cerrowire.com

For 100 amps, this would indicate using at least 2 awg and possibly 0 awg.

You can take a look at the wires to double check if they are large enough.

____________

Less obvious is that there are always losses at connections / terminals - even if they are nearly perfect.

The way wiring is designed, the heat from the termination is conducted into the wire and the heat is dissipated through the wire insulation to the air, so even the slightest imperfection will result in the hot wires that you are experiencing.

One approach is to buy some high quality / tin plated, 0 awg wire and a BUS breaker. Wire it up and see if the problem goes away. A lot of DIY level wire crimpers are not nearly as good as the results from a real pro level crimper and marine grade terminals.
 
turtlepower said:
Hi
I'm running this 100 amp PowerMax PM3-100LK battery charger in my box truck. It's set to 14.6 and "staged charging". It charges 2 100ah lithum batteries. When it's plugged in this part I'm touching gets almost too hot to touch. Both sides of this amazon 150A circuit breaker get hot. The wires are less hot the further I follow the wire in either way. I bought a 2 pack of these breakers, so I tried a different one. I also added copper washers you can see in the photo hoping for a better connection.
Any ideas?
Click to expand...
I believe I know the reason.
Your BMS is disconnecting the connection due to OVP. Hence, the energy has to go somewhere. The mini/micro arcing. Your 14.6V = 3.65v for each cell, you are pushing your luck. I don't know if your 2 100ah have built in passive or active balancer.

Lower your charging voltage to 13.6V or 13.8V. This is lithium battery (Probably lifepo4?) and not lead acid. You cannot apply lead acid thinking/knowledge with lithium battery.
 
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Reactions: Bop
For a 12v system you could replace with a fuse of your choice, quality ANL or MEGA fuse is all you need.

One great test is by passing the breaker by directly bolting those cables together.

There is a small chance one of those cables have a bad crimp but I’m 99% sure it’s that pop style breaker that’s causing heat.
 
I have the same PowerMax charger in the 45amp version. It is a three stage and it’s not ideal for LifepO4. Because we could see the bms through the app we could tell it was triggering a high cell protect. It also was too high in normal mode and had a float mode that I didn’t want(see the bottom paragraph in picture). It does have a fixed voltage(power supply) mode that I set it to 13.8. I used a shunt with triggering options that started a timer at 13.7 for one hour which opened a relay and disconnects the AC to the charger. (Active balancer keeps things good with this time frame) The other option was to buy a proper charger or monitor the voltage and pull the plug. We use this to charge the lithium trolling battery in his boat.
IMG_1457.jpeg
 
Oh, and as others have mentioned. Loose that circuit breaker. Look at Blue See or Buss brand for 12 volt systems. You get what you pay for and it’s better than getting more than you bargain for.🔥
 
turtlepower said:
Hi
I'm running this 100 amp PowerMax PM3-100LK battery charger in my box truck. It's set to 14.6 and "staged charging". It charges 2 100ah lithum batteries. When it's plugged in this part I'm touching gets almost too hot to touch. Both sides of this amazon 150A circuit breaker get hot. The wires are less hot the further I follow the wire in either way. I bought a 2 pack of these breakers, so I tried a different one. I also added copper washers you can see in the photo hoping for a better connection.
Any ideas?
View attachment 217058
Click to expand...
I had that style breaker in the beginning of my build and they got very hot. The surface area on the breaker where the wire connects was small and not perfectly flat. It just couldn't seat properly
 
AshleyL said:
I believe I know the reason.
Your BMS is disconnecting the connection due to OVP. Hence, the energy has to go somewhere.
Click to expand...

Huh? If the BMS were disconnecting, you would basically have an open circuit. The charger can't push amps into an open circuit.

I agree with others about the circuit breaker. However, I would bolt those two lugs together temporarily and check again to make sure it's not a bad crimp.
 
Skypower said:
I have the same PowerMax charger in the 45amp version......
It does have a fixed voltage(power supply) mode that I set it to 13.8.
Click to expand...

I have a 75 amp version. I also use the fixed voltage set to 14.1v, but I also use one of these to turn it on/off (via power relay) at my own low/high voltage setpoints. I never really need to fully charge using the PowerMax (just get the batteries back up after several days days of no sun), so I set it turn the PowerMax off at 13.9v which is more than sufficient.

 
Texas-Mark said:
I have a 75 amp version. I also use the fixed voltage set to 14.1v, but I also use one of these to turn it on/off (via power relay) at my own low/high voltage setpoints. I never really need to fully charge using the PowerMax (just get the batteries back up after several days days of no sun), so I set it turn the PowerMax off at 13.9v which is more than sufficient.

Click to expand...

lol. Yup, that works.
 
Texas-Mark said:
Huh? If the BMS were disconnecting, you would basically have an open circuit. The charger can't push amps into an open circuit.

I agree with others about the circuit breaker. However, I would bolt those two lugs together temporarily and check again to make sure it's not a bad crimp.
Click to expand...
No, it will arc over for a moment when the circuit is disconnected by the BMS. The location of the mini/micro arcing depend on your setup. Some at the BMS circuit board while another might be at the connector.
When you are pushing that much 100amp and it got disconnected suddenly, it will create mini/micro arcing.
Just reduce charging voltage from 14.6v to 13.6 or 13.8v
 
AshleyL said:
When you are pushing that much 100amp and it got disconnected suddenly, it will create mini/micro arcing.
Click to expand...
Well, law of physics telling us about two factors of creating arcing: air gap and a voltage.
Current will depend on the two and full round of resistance from energy source.
 
AshleyL said:
No, it will arc over for a moment when the circuit is disconnected by the BMS.
Click to expand...

Say what? How is a closed breaker going to arc over?" Acr over to where? By your logic systems will be arcing and sparking everywhere every time a BMS disconnects for whatever reason. :rolleyes:
 
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