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Old 17-10-2015, 20:08   #16
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Re: Derating An Alternator

Maine Sail has commented on this and I don't believe the MG regulator has belt manager and amp manager but probably best to contact Mark directly and find out for sure. I know that Maine Sail sells both MB and Balmar.

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Old 17-10-2015, 22:10   #17
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Re: Derating An Alternator

I am not familiar with the alternator you quoted but the ones I use have a voltage sensing terminal and if you can find a way to increase the voltage on this terminal it will suppress the current output from the alternator. One of the ways to do this would be to put a resistance in the output from the alternator and sense to voltage on the alternator side of the output.

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Old 18-10-2015, 02:22   #18
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Re: Derating An Alternator

All the DIY solutions require you to remember what you've done and where you're at.
Much simpler just to buy a decent external reg and let it do the job for you.
The problem you have is that the Leece Neville alt is not hot or KKK rated for full output for any length of time and it comes standard with an automotive type reg which is useless for properly charging a deep cycle house bank.
Get a reg that allows you to manage your alternator...either by just straight derating it or derating it comensurate with alt temperature..I think there is a Balmar product that does that.
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Old 18-10-2015, 05:36   #19
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Re: Derating An Alternator

Originally Posted by colemj View Post

If this is an internally-regulated alternator, the OP does not have to worry about running it for long times in the tropics - it will take care of itself just fine.

The Leece-Neville 8MR series does not have a super-dumb internal regulator (eg; Hitachi, Rhone etc.) just a regular old school dumb one, which means voltage only & no protective temp gradient. This means it will run its little heart out until the battery bank attains the voltage regulated set point. It also means that if it runs like this long enough it can cook itself.

Originally Posted by Hoghead View Post
Is there any way to de-rate a 200.00 Leece Neville/Prestolite 8MR series 105A alternator?
The goal is not to run it at full chat in the tropics so as to kill it prematurely
I have a 675 AHr Trojan flooded bank so about 70A from the alternator would seem about right
The best option is going to be an external regulation kit with a external regulator such as a Balmar reg with belt-manager or another brand external reg with temp compensation.

Be aware that some regulators simply ping-pong on/off or on/50% cut for temp sensing when the high limit has been reached.. A rather kludge way of handling this. The newer Balmar regulators use adaptive temp compensation which will find the highest output sweet spot and you can also use belt manager to save your belt. Very few regulators offer the ability to derate or limit alternator output..

I generally prefer the MC-614 over the ARS-5 because it is designed to drive 15A+ on the field, this means it works a lot less hard than an ARS-5 with a max of about 7A...
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Old 23-04-2017, 07:58   #20
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Re: Derating An Alternator


I've read your article - thank you. Great clarity. In which category do you place the 115A Mitsubishi Alternators as fitted to the VP D2-40B? Observation says dumb but maybe not super-dumb since they seem so stabilise at 14.2 on a long motoring trip.

Reason is that I'm looking for a sensible way of derating these (I have 2). I was looking at feeding the yellow sense wire a slightly higher voltage than the battery voltage in order to reduce the charging current. This approach would (might) remove the need for opening up to expose the field wire and would provide a more flexible solution that a resistor-based derating.

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