WHY THE HEAT ?

[BackTOschool]

I'd still suspect a problem with the short wire, then. Have you tried, as a test, bolting the two lugs that mount to the fuse together directly? Either that, or try @Hedges' voltage drop test. The latter, done right, will be completely unambiguous as to where the problem is.

With high current flowing, use DMM to measure voltage across each contact. Lug to terminal, terminal to wire strands or far end of wire, between terminals of use, etc.

Voltage drop test is pretty easy. Take your multimeter, set it for DC volts on the lowest range it has, and start probing the wires at various close together points. Everywhere there is any kind of connection between your probes is a valid target. You should see nearly zero everywhere, but somewhere related to that short cable will probably have .3V or so. At 50A, that's 15W of heat at that connection.

Thank you, will do. I'll let you know tomorrow.
Steve.

 

[DPC]

Joints sometimes loosen up if they get hot

Where possible use copper bolts and hardware
A copper compatible anti oxide compound to make sure your connections stay clean and dry

 

[Luxpower_Gilbert]

Try putting the fuse on top of the terminal instead at the bottom… or use t-class fuse…

 

[BackTOschool]

Voltage drop test is pretty easy. Take your multimeter, set it for DC volts on the lowest range it has, and start probing the wires at various close together points. Everywhere there is any kind of connection between your probes is a valid target. You should see nearly zero everywhere, but somewhere related to that short cable will probably have .3V or so. At 50A, that's 15W of heat at that connection.

Hi TorC
Here are the results for the following points you suggested I do, Your observations and thoughts would be very welcome:
Big picture: A) I'm not sure if it "normal" to generate this heat under these conditions? B) understanding heat is wasted power, when I remove the fuse and wire direct there is no heat. Q: is it possible to fuse without causing the heat?
kind regards
Steve.


Ambient temp : 11.5 deg C
Battery load: 102.6 Amps / 12v
Inverter load: 1135 Watts / 240v

position	V drop test	​	Temp after 15 mins	40 mins	60 mins	90 mins
Battery terminal to connecting lug	00.4mV		11.5 Deg C	13	14	16
Battery lug to fuse point lug	54 mV		56	63	60	60
fuse end to end	52.4 mV		34	34	35	35
fuse exit lug to inverter entry	19.2mV		​ 36​	46	51	45​

 

[TorC]

The fuse will have some voltage drop, just because it's actually supposed to generate a bit of heat. Ultimately, if it blows it literally melts the internal wire. That looks to be maintaining a good temperature, exactly as you'd expect for a properly sized fuse.

The place that looks off is exactly the wire you're seeing get hot, from battery to fuse. I'm rather suspicious that one of those lugs isn't crimped as well as it should be or is deteriorating. Either that, or it's got two slightly high resistance connections and not enough length do dissipate the heat well.

 

[Hedges]

Q: is it possible to fuse without causing the heat?

Yes, magnetic-hydraulic breaker. They have a fraction the resistance of thermal-magnetic. I'm not sure how fuse resistance compares to thermal-magnetic breakers.

 

[Ellcon123]

It looks to me the nut needs tightened more. There's a lot of gap in that split washer (more than I'm used to seeing), and it is resulting in uneven pressure.

Spot on. Those washers should be flat both sides of the fuse. Not a battery lug so I generally tighten as hard as I can.

 

[BackTOschool]

Spot on. Those washers should be flat both sides of the fuse. Not a battery lug so I generally tighten as hard as I can.

as previously clarified, the picture was when NUTS NOT TIGHTENED...if only it were that simple ...

 

[BackTOschool]

The fuse will have some voltage drop, just because it's actually supposed to generate a bit of heat. Ultimately, if it blows it literally melts the internal wire. That looks to be maintaining a good temperature, exactly as you'd expect for a properly sized fuse.

The place that looks off is exactly the wire you're seeing get hot, from battery to fuse. I'm rather suspicious that one of those lugs isn't crimped as well as it should be or is deteriorating. Either that, or it's got two slightly high resistance connections and not enough length do dissipate the heat well.

Thanks for your reply.
Are these voltage drop values to be expected ?
I will make a new cable ( the one I will be removing is new ) from battery to fuse, paying careful attention to ensure the lugs are securely fastened, and test again.

 

[TorC]

For the fuse, I'd say you're doing just fine. According to this chart from Victron, a 150A MEGA fuse has a 90mV drop, probably at 150A, and nearing blowing. It, and its holder, are designed to dissipate that. At cold resistance for 102A, you'd still have a 36mV drop just in the fuse itself, and heat increases resistance. That looks good.

It still seems odd to me that that cable is causing trouble when you've already tried two cables. Has me starting to wonder if it's more about the battery connection itself being high resistance, and is masked by the single cable, because the heat has somewhere to flow. If you have heat shrink that will slip over your lugs, I'd consider peeling insulation or heat shrink to get to the actual wire, so you can check each end for some kind of inferior connection separately.

 

[Hedges]

And cable voltage drop no more than fuse voltage drop, probably more surface area to dissipate heat. Unless all concentrated in the connection.

Did OP bypass fuse? "Have you tried, as a test, bolting the two lugs that mount to the fuse together directly?" was supposed to happen a week ago. I thought I read somewhere somebody confirmed cold operation that way, in some thread. Don't see confirmation in this one.

 

[TorC]

@Hedges I believe a new cable was made to span the whole thing, rather than that more useful test.

 

[BackTOschool]

Yes I made a whole new cable with no fuse, connected and tested = no heat, perfect.
I have not bypassing the fuse and connecting the two cable ( fuse ends) together, will try and see if any difference...

 

[BackTOschool]

For the fuse, I'd say you're doing just fine. According to this chart from Victron, a 150A MEGA fuse has a 90mV drop, probably at 150A, and nearing blowing. It, and its holder, are designed to dissipate that. At cold resistance for 102A, you'd still have a 36mV drop just in the fuse itself, and heat increases resistance. That looks good.

It still seems odd to me that that cable is causing trouble when you've already tried two cables. Has me starting to wonder if it's more about the battery connection itself being high resistance, and is masked by the single cable, because the heat has somewhere to flow. If you have heat shrink that will slip over your lugs, I'd consider peeling insulation or heat shrink to get to the actual wire, so you can check each end for some kind of inferior connection separately.

yes they are heat shrunk, maybe I'll make a new section ( bat to fuse ) as last comment, check lugs are really connected well and test...

 

[BackTOschool]

For the fuse, I'd say you're doing just fine. According to this chart from Victron, a 150A MEGA fuse has a 90mV drop, probably at 150A, and nearing blowing. It, and its holder, are designed to dissipate that. At cold resistance for 102A, you'd still have a 36mV drop just in the fuse itself, and heat increases resistance. That looks good.

It still seems odd to me that that cable is causing trouble when you've already tried two cables. Has me starting to wonder if it's more about the battery connection itself being high resistance, and is masked by the single cable, because the heat has somewhere to flow. If you have heat shrink that will slip over your lugs, I'd consider peeling insulation or heat shrink to get to the actual wire, so you can check each end for some kind of inferior connection separately.

i have observed the heat starts at the fuse lugs, and then spreads along the cables, until the who cable heats. the last place to heat seems to be the bat terminal. I'll try bypassing the fuse and bolting the lugs together... thanks for you continued thoughts.

 

[BackTOschool]

i have observed the heat starts at the fuse lugs, and then spreads along the cables, until the who cable heats. the last place to heat seems to be the bat terminal. I'll try bypassing the fuse and bolting the lugs together... thanks for you continued thoughts.

who? whole cable