Alternator Field Control

crutschow

Joined Mar 14, 2008
34,420
How can we give you a informed answer when you have given us no info on the alternator except that it it "high powered" which gives us no technical information.
 

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ejbones

Joined Mar 9, 2023
9

Thread Starter

ejbones

Joined Mar 9, 2023
9
The idea is generally to depower the alternator more, in a smooth and manual way. I do wonder if the regulator will also have a PWM control which might be bad to double up on with an additional one
 

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ejbones

Joined Mar 9, 2023
9
Because I'm experimenting with a non stock alternator, and my currently installed regulator doesn't reduce field current fast enough before the alt gets too hot. And because I want to be able to prioritize motoring (it's a boat) instwad of charging or vice versa- manually
 

LesJones

Joined Jan 8, 2017
4,189
The reulator is not designed to protect the alternator. It is designed to maintain a constant output voltage with varying electrical load and alternator speed. If it is overheating you need to reduce the load on it. (Or get a larger alternator that can supply the load.)

Les.
 

MaxHeadRoom

Joined Jul 18, 2013
28,684
An alternator regulator usually works with the field only, IOW all it does is control a variable amount of current in the lower current field in order to provide the correct excitation to the high current stator.
The field is not directly affected by load other than to increase excitation as the stator current increases.
 

Thread Starter

ejbones

Joined Mar 9, 2023
9
The reulator is not designed to protect the alternator. It is designed to maintain a constant output voltage with varying electrical load and alternator speed. If it is overheating you need to reduce the load on it. (Or get a larger alternator that can supply the load.)

Les.
The regulators temp sensor is designed to protect the alternator - its just that the temp mechanism doesn't cut in early enough and allows the alternator to get too hot
 

michael8

Joined Jan 11, 2015
414
So instead of or in addition to sensing the alternator temperature you could sense the load current as
it's a measure of the heat being produced right now or in addition to temperature. Keep in mind that
the heat in the alternator is likely related to the current squared (I squared R), not linear.
 

Ian0

Joined Aug 7, 2020
9,805
The reulator is not designed to protect the alternator. It is designed to maintain a constant output voltage with varying electrical load and alternator speed.
And it does that in order to charge the battery, when the battery is charged the current will be reduced to almost nothing.
If you reduce the alternator output when it is charging the battery, guess what? Next time you want to start the engine, it won’t start because you will have a flat battery.
 

geekoftheweek

Joined Oct 6, 2013
1,214
If you have a water cooled alternator on a boat that is getting too hot you have bigger problems than trying to limit the field. How is your coolant plumbed into the alternator? How much power are you trying to draw? Have you checked your battery?
 

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ejbones

Joined Mar 9, 2023
9
If you have a water cooled alternator on a boat that is getting too hot you have bigger problems than trying to limit the field. How is your coolant plumbed into the alternator? How much power are you trying to draw? Have you checked your battery?
I'm still building it out since it's all custom. Water isn't even hooked up yet, However i was advised that it wouldn't put out more than 120a continuous without burning the diodes. As it is now even with proper water it will burn out charging a 600ah 12v battery at 190 amps. I want to be able to ramp up to full current manually.

The alternator is my secondary charge source for the house batteries.
 

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ejbones

Joined Mar 9, 2023
9
The use case for a boat house bank is different than a small starting small battery like in a truck. I need sustained output for 1+ hours. I can use a different customizable regulator, but it want to see if I can make my current regulator work with a small mod
 

geekoftheweek

Joined Oct 6, 2013
1,214
The alternator is my secondary charge source for the house batteries.
That changes everything. My apologies.

Normally a regulator is going to do what it takes to maintain a specified voltage. If you try to limit the field current it will detect it as a lower voltage output than it expects and try harder more or less.
 

strantor

Joined Oct 3, 2010
6,798
Normally an alternator is just a dumb voltage source that will do everything it can to maintain the set output voltage, up to and including burning itself out and/or burning up its regulator. Which it sounds like you have experienced, or are experiencing.

What you described of your goal sounds to me like you want it to behave less like an alternator and more like a high capacity CC/CV power supply or battery charge controller. I do not know of an off-the-shelf device which takes the place of a (dumb) rectifier to turn the alternator into a (smart) charge controller. Although it seems doable in theory, it would most likely be a custom project.

But what would probably be easier is to decouple the alternator from the battery bank and place a DC-DC CC/CV buck/boost module in between them. Instead of trying to turn your alternator into a charge controller, just install a separate charge controller. Something like this maybe.
 

geekoftheweek

Joined Oct 6, 2013
1,214
I thought of suggesting this https://www.redarcelectronics.com/u...WFhnoI02rA0Vf54oFzkCc1btOGKbb4XxoCmCwQAvD_BwE earlier in the day.

I think this is the type of device Strantor was trying to link.

I'm sure there are others available that may be better suited to your needs. It's a bit pricey, but so is your alternator. It's going to be about the easiest way to fix your problem short of building your own regulator. You could also trick your regulator into thinking it's putting out more voltage than it is and slowly ramp it up that way, but there's no guarantees on that idea.
 

Thread Starter

ejbones

Joined Mar 9, 2023
9
The regulator has a voltage sense that is separate from the field wire. my hope is to have the pwm prevent the highest current charge, but it'll still shut off normally as it senses a high enough voltage.
Yeah a dc dc charger is standard in these situations but I'm not convinced that the $1k+ is really warranted if I can get to a steady state safe output on this alternator.

May test tomorrow, otherwise next week early
 

MisterBill2

Joined Jan 23, 2018
18,477
Because I'm experimenting with a non stock alternator, and my currently installed regulator doesn't reduce field current fast enough before the alt gets too hot. And because I want to be able to prioritize motoring (it's a boat) instwad of charging or vice versa- manually
If the alternator gets"too hot" that fast then you are delivering way to much current. That part is simple. If you are also powering a boat then perhaps the alternator is spinning excessively fast and needs a different drive arrangement. Possibly a constant current regulation scheme, with a voltage limit control, is in order. That could reserve most of the engine power for moving the boat.
 

pwmking

Joined Dec 21, 2023
1
The regulator has a voltage sense that is separate from the field wire. my hope is to have the pwm prevent the highest current charge, but it'll still shut off normally as it senses a high enough voltage.
Yeah a dc dc charger is standard in these situations but I'm not convinced that the $1k+ is really warranted if I can get to a steady state safe output on this alternator.

May test tomorrow, otherwise next week early
HI - do you have any progress to report. I'm thinking about the same to charge my lifepo4 batteries on my boat. I have a Valeo alternator with a rating of 125A. I'm thinking about PWM the field wire depending on the temperature of the alternator.

Kind of like PWM Fan controller (Reverse Operation:at max temperature the PWM is connected to ground and the field is not excited). thoughts?
 
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