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diy solar

How much heat is too much? Also, voltage drop...

mr_chadj

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Aug 31, 2021
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Location
Green Bay, WI
I’m building a smaller scale “portable” system that I want to bring along camping.

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It’s a 12v system. With a LiFePO4 battery that can do 200a continuous discharge and a 1200 watt inverter. That’s 2 AWG wiring between battery and inverter with 175amp Anderson connectors along with a 175a AMG/MEGA fuse. That’s a quick rundown.

When I slap a 1000 watt load on the system for 13 minutes (discharging about 10% of the battery) the cables close to the inverter/fuse get warm (more the positive side than negative). The positive leads also get warm close to the Anderson connector as well. I’m worried I have some bad crimps.

Using an infrared laser thermometer the cabling closest to the fuse gets the warmest (112 degrees Fahrenheit). The positive cable right by the inverter gets to 102 degrees. The positive cable right by the battery is about 82 degrees. The room is about 65 degrees.

During this discharge, the voltage measured at the battery terminals is 12.73 and the voltage measured at the inverter terminals is 12.57. So that's about 0.16 volts being dropped. There is no voltage drop when the load is removed.

My load is an Instant Pot that pulls a pretty consistent 1050 watts when heating water. The ac cable from the instant pot even gets warm by the inverter. Though not as warm as the dc cables.

Since I'm a newbie I don't really know if this is normal. Are my cable crimps potentially bad? Thanks for any help you can offer!
 
2 gauge is rated for about 100 amps so you're right on the edge. I'd say keep cables short and you'll be fine.

If this was something that was going to be operating every day all day long, I'd suggest much larger cables..
 
The ampacity of cable diferes with the insulation rating. Marine grade 2awg cable is good for over 200 amperes in open air. That temperature rating is 105 centigrade. The fact that the cable gets warmer at one end is a indicator of more resistance. Use a multimeter with the probes across the connections to see the voltage drop. That identifies problems better than a heat measurement. But you show less than 2% voltage drop. If true you have no problem.
 
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well, 12v system with 1000W load..
so thats 1000W/12v Amps * probably 20% inefficiency of your inverter or (1000 / 12) * 1.2 = 100Amp load!

Keep in mind that the "rating" of cables is to make sure the insulation does not melt, NOT that it is efficiently carrying the load.
your 2awg cable with a "loop distance" of around 6' will get warm, but that is ok and the actual voltage drop over that small of a distance looks to be around 1%.

its fine regarding feeling "warm", if you cannot touch it for an extended period of time that you really need to worry!

that your "heating" was not symmetrical probably does mean you have issues with your connectors: poor connections cause heating(resistance * current^2 == heat). The tricky part is that unless you have a milliohm meter you cannot measure it without a load as it will be a small number. In your case you have a large current load so measure the voltage drop across the connectors and that will give you an idea as you can compare them directly.
 
@Bud Martin good catch. I was getting that "1050" number from the Victron App which works in VA. So yeah, my load was 1050 VA, not watts. I'm still fuzzy on the difference between the two.
 
@Bud Martin good catch. I was getting that "1050" number from the Victron App which works in VA. So yeah, my load was 1050 VA, not watts. I'm still fuzzy on the difference between the two.

simpliest way to think about it is that VA is only an issue when talking about AC power; in DC watts == VA as there is no complex component.
This is why when testing your inverter you use "space heaters" that are just resistive loads and not something like a motor that has capacitive and inductive components.

I guess the TLDR is, do not worry about the difference as VA will be just a bit more than watts but for DIY types its nothing to worry about ;-)
 
I overcable stuff.

My 1200W inverter has 2/0 cables.
They have never gotten hot, ever.
Fair enough! According to Victron, this inverter will only accept up to 2 AWG wires so that's why I went with that. I'm going to rewire the battery/inverter hookup without the Anderson connectors and then check temps and voltage dropoff. I'll update this thread with the results.
 
Somewhat surprised the connection would be limited at 2ga

Aren’t the battery cable connection points studs?
I have 5/16 ring terminals for 2/0. Although giandel supplied 2ga cables I relegated those to battery parallel service and made my own 6’ 2/0 cables for the inverter feed.
 
Somewhat surprised the connection would be limited at 2ga

Aren’t the battery cable connection points studs?
I have 5/16 ring terminals for 2/0. Although giandel supplied 2ga cables I relegated those to battery parallel service and made my own 6’ 2/0 cables for the inverter feed.

The docs called out 2 AWG (bottom of the chart) ...

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Maybe a larger gauge would fit?

I conducted the same test as above with new 2 AWG wire going straight from the battery to the inverter (no fuse, no Anderson connectors). The voltage drop under load reduced down to .10 volt. The cables still warmed up a bit but not nearly as warm as before. So yeah, I'm going to rethink how I wire this longer term.
 
It was an instant pot (just a simple resistive heating element). I ended up solving this issue by re-crimping the connections, shortening up the wires involved, and switching from a 175a fuse to a 200a fuse. With those changes, heat wasn't an issue.
 
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