High Alternator excitation current - why?

My 300 amp alternator operated fine before it threw a regulator. I replaced the regulator and since then it has continued to generate very high temperatures within the in-line fuse holder, so high the plastic melts and the fuse does not blow.

I have tried lower cuurrent rated fuses to find the blow point, however the plastic still melts.

I have tried Narva Fuses in the belief the issue was the quality of the fuse, again this did not work, and eventually the fuse holder and terminal seperate and the charging stops.

Whilst in Mildura on the trip I decided to try a larger footprint fuse, a jumbo spade style to see if the plastic/rubber fuse holder was the weak point. I have to run a 40amp fuse on the excitation circuit to keep the alternator operating.

Funny enough the faiure point always seems to be when I stop the car and then re-start it, the fise connection in the terminals must seperate, as i am usually able to pull the push out of the terminals and re-seat it with power resptored.

Yesterday, with the jumbo fuse installed, I stopped the car for fuel and upon restrating the alternator way again not charging. I had full batteries so left it and drove home without ill effect. This morning I inspectted the jumbo 40amp blade fuse and it was blown.

Also, the car charges all day at 14.7V/14.8V, does not drop. I find this abnormal.

I am thinking about swapping out the regulator - was a difficult item to source as came from the US.

So, Questions

1) what would the excitation current be expected for a 300A 14V alternator?
2) Why am I getting some enormous temperature rise at the blade fuse holder, on the basis the fuse holder connections are clean?
3) is the non regulation of the voltage indicative of a faulty 'new regulator'? The charge voltage can rise as high as 15.2V, but then I dont know if the after market gauges are accurate.
4) I am running power down to the rear pod thru a renogy 60amp DCDC charger to replenish the 400a/hr lithium banks, so in theory there should only be a 60amp draw to the rear, and then a minor top up for the starter battery.

I have though about changing the fuse style to the flat style, but really think I am not at root cause and just wasting effort.

I have also tried using the 'quick breaker/reset blocks to protect the current flow to the rear battery, however this tripped so many times I gave up on it - believing it was faulty. I have a different make unit I am yet to try, this being the protection for the cable to the 60amp DCDC charger.

So pls consider and fire back some suggestions. I am ready to swap the 300amp unit back to the 130amp unit originally supplied and see if the problem resolves itself, but thats just an option.

thanks guys.

That field current appears way too high. The regulator works by controlling the field current based on its sensed output voltage. I would suggest that your field current should be no more than about 10 amps (around 2-3 amps for a 'standard' alternator).
My money is on a faulty regulator, or incorrectly installed.

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Originally Posted by Brissieboy

That field current appears way too high. The regulator works by controlling the field current based on its sensed output voltage. I would suggest that your field current should be no more than about 10 amps (around 2-3 amps for a 'standard' alternator).
My money is on a faulty regulator, or incorrectly installed.

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Thanks for the feedback, I installed the part, its a simple bolt in installation with a single solder joint, cant see how I would have got that wrong? I will pull the alternator out and swap it with the smaller capacity unit and monitor the outcome. I have another 2 spare regulators for this alternator so will de-solder and install a new unit.

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Originally Posted by PeeBee

Thanks for the feedback, I installed the part, its a simple bolt in installation with a single solder joint, cant see how I would have got that wrong? I will pull the alternator out and swap it with the smaller capacity unit and monitor the outcome. I have another 2 spare regulators for this alternator so will de-solder and install a new unit.

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How is the solder joint? Could it have ended up being a cold join, creating high resistance/heat?

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Originally Posted by Hodge

How is the solder joint? Could it have ended up being a cold join, creating high resistance/heat?

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Unsure, will get to it in a couple of days, currently trying to find homes for all the crap i took out of the truck from the trip, which has developed into a challenging purge-fest. From memory it was a nice pooled connection - no idea right now but will check and get back to you.

OK, swapped out the alternator back to the 105amp unit today, straight forward frustrations etc. Fired it up and 13V charge only - WTF now. Anyway its the case of using a soft standard duty belt instead of a heavy duty green back belt, which does not stretch but is noisier on start up. So tomorrow, another 30 mins to resolve the charge, lack of boost and lack of vacuum. The standard duty belt lasted 1500klm then 2 days sitting under constant auto tension, it was toast - another one destined for the bin. Started the search for the multiple spare regulators i have, another game of hide and seek taking place.

The mechanical load at the pulley of such high amperage alternator is that high that it chews through new belts?

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Originally Posted by BrazilianY60

The mechanical load at the pulley of such high amperage alternator is that high that it chews through new belts?

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I swapped the belt out today for one of the heavy duty spares I carry as emergency belts - it was obviously removed for a reason and it was also stretched beyond use, so pulled out a 'newer spare' and the system has been returned to normal. The issue is the drive torque is very high and the belts still are elastic - they are simply fabric and rubber. Anyway, I probably get 6 months out of a HD 8 rib belt, it is what it is and i dont drive it that hard in all honesty.

OK, I think I see the problem, generated by myself once again, and baffled how i managed this or how it even works.

I looked up the wiring diagram and there should be a heavy charge cable from the alt + to the Quicktifer +, then another cable from quicktifer + to the battery, fused, so a heavy cable.

I have left off the cable from the alt + to the quicktifer and have all the charge current coping thru a fused cable that I was calling the excitation cable - any wonder it struggled with a 300amp load, let alone a 130amp. The excitation circuit is handled by a small 1amp fused ignition sourced cable.

This qualifies for the drongo of the week award i reckon.

Quicktifer?? WTF?