Negative wire getting quite hot

[DoughMyDays]

My electric outboard negative wire is getting warm to hot under only approximately 30 - 40amp load.

I have it connected to a Daly bms with a 100ah lithium battery and the bms also being rated at a 100a discharge.

I cleaned the terminals with some light sandpaper but still have the same issue. It went away one but now it seems to be constant.

Weird thing, is that the positive wire doesn't even appear to be luke warm after a motor out.

Any have any ideas?

 

[jamie N]

Having cleaned the terminals, and checked the integrity of the conductors, with the disparity between them perhaps your best option is contact the manufacturer?
Apologies for such naff advice, as that doesn't help the problem which you feel is noticeable.

 

[Poey50]

My electric outboard negative wire is getting warm to hot under only approximately 30 - 40amp load.

I have it connected to a Daly bms with a 100ah lithium battery and the bms also being rated at a 100a discharge.

I cleaned the terminals with some light sandpaper but still have the same issue. It went away one but now it seems to be constant.

Weird thing, is that the positive wire doesn't even appear to be luke warm after a motor out.

Any have any ideas?

What is the cross-section and length of cables?

 

[neilf39]

Could be some corrosion under the cable cover making high resistance. There is a thing known as black wire corrosion if the black wire is not fully disconnected from the battery when not in use. Corrosion creeps along the wire. I came across it on R/C model aircraft but can't recall the physics behind it. Can you put a multimeter across the cable to measure resistance?

 

[john_q]

I know this is for a petrol engine but it may help.

How to Check resistances in cables from Lug to Lug

A vehicle that is getting poor performance from its battery can look to a number of causes, but a common cause is a corroded battery cable that is high in resistance. It is usually a good idea to test, and if necessary replace, less expensive items like the battery cable before replacing a high-priced starter or battery.
Step 1
Have someone sit in the vehicle to be ready to crank the engine. Set the multimeter to measure voltage.
Step 2
Test the positive battery cable by connecting the red lead from the multimeter to the positive battery terminal. Connect the black lead of the multimeter to the engine starter's positive terminal. Have your helper crank the engine and note the reading on the meter before the engine starts. The meter should read close to zero, and any reading of more than 0.3 volts is reason to replace the cable.
Step 3
Test the negative battery cable by using the same procedure as above for the positive cable, but this time you will have the red lead of the multimeter touching the metal housing of the starter motor, and the black lead of the multimeter connected to the negative battery terminal. Again you should see a reading of 0.3 volts or less to be confident that your cable is good.
Step 4
Avoid using a multimeter or ohmmeter to directly measure the resistance in the battery cable. Automotive quality ohmmeters do not have the required sensitivity to directly measure the very small resistance differences in battery cables that make a very big difference in performance.

Good luck

 

[Boater Sam]

Cables the same cross sectional area AND length? The resistance of that lead may be saving your alternator from overheating and burning out.

 

[DoughMyDays]

Hi all. Thanks for the responses.

What is the cross-section and length of cables?

No more than 1 meter.

Yes cables are the same length. I tried it again bypassing the BMS and connecting it directly to the battery and it still gets hot,

The Actual terminal itself does not appear to be where the hottest part is but a little before the terminal ring. I have marked out in a pic below.

Cables the same cross sectional area AND length? The resistance of that lead may be saving your alternator from overheating and burning out.

Yes both exactly the same. They came fitted with the outboard.

 

[Boater Sam]

Cut back and re-terminate, there is possibly a partial break in the cable at the hot spot.

 

[VicS]

Cut back and re-terminate, there is possibly a partial break in the cable at the hot spot.

+1

 

[Alex_Blackwood]

Hi all. Thanks for the responses.


No more than 1 meter.

Yes cables are the same length. I tried it again bypassing the BMS and connecting it directly to the battery and it still gets hot,

The Actual terminal itself does not appear to be where the hottest part is but a little before the terminal ring. I have marked out in a pic below.

Yes both exactly the same. They came fitted with the outboard.

That looks like very fine multi strand wiring, not the best to use with a crimp, heavier gauge strands much better.

 

[DoughMyDays]

That looks like very fine multi strand wiring, not the best to use with a crimp, heavier gauge strands much better.

I thought that looking at them. I am very surprised considering the outboard at full power draws around 70Amps!