Just thought I’d ask around. I’ve done a lot of googling but most of its unrelated.
I need to make somewhat stable dc power to feed my charge controller without spending a ton of money.
is it possible to regulate a alternator not hooked up to a battery? When the controller goes into float it basically will be under no load. It has a 150 volt limit. I just need to keep it under 70-80 volts for a margin of safety. Just not sure how to regulate it. A PMA can’t be regulated as far as i know beyond rpm control. Turn key solutions exist but they cost some serious money. Thoughts?
Most GM alternators have built in voltage regulators. Battery or not, voltage is stable, around 14 volts.
However I’ve heard it’s a bad idea to run them disconnected from the battery, at least on a car.
what voltage you need ?
regulators on alternators are excellent charge controllers.
next generation is controlled by the ecu, but those can be tweaked more easy 
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Anywhere from 25-100 volts. I might be better off just using a permanent magnent alternator and keeping the rpms low. I haven’t seen to many midnite classics hooked up to engines.
what sort of output amps do you need to charge up your battery bank ? if its not a great deal then a cheap source of PMA’s would be to grab hold of 2 or 3 treadmill motors and make all 3 driven off the one engine , or if you have some money the wind turbine PMA’s would do the trick I would have thought .
Dave
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60 amps minimum, preferable 80-90 amps. Rpm control would be key, I either need to get a slow speed engine or have a protection circuit on it. I dont know much about throttle control. Would it surge really high if the load stops?
I could make sure the pma voltage is under the charge controllers limit at max rpm for the engine. I dont want to fry it.
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look for the 24 V version, truck alternator, load constant at 28,8 Volts, available as selfexciting, up to 200 amps… ( that’s about 5,6 Kwh )
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I talked to the guy at midnite classic. He said to avoid any brushed generator or alternator. Something about it being “stiff” and it can’t clamp it or do anything and it fries. I might be stuck with a pma.
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??? His statement confuses. A prejudice??
Brushes give the easy field strength control. Brushless, still possible with a wound field. PMG - NOT: easy, or cheap, to control at all.
S.U.
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Yeah I did a follow up and he said the same for pma’s which is weird because the controller supports hydro. Whats the difference between hydro pma driven power and engine driven pma power? As long as the rpm is stable there is no difference or risk. I don’t know. I might not bother with the midnite and just use it for more solar.
The biggest issue I have so far with alternators or generators running a battery charger is they suck at charging deep cycle batteries. My charge controller charges at 14.9 volts (per the manufacturer). Thats what it takes to charge them under 6 hours. Most “smart” chargers, converters and other devices charge at 14.4, which is pretty much designed for grid power. Yeah 14.4 will fully charge the battery, in 20-30 hours. Same goes for alternators. The regulators cut off way to early. They are designed to lightly charge a battery at 95% and maintain loads. I need more than that. I need 120 amps at 16 volts and hold it there. I don’t know of any way to do that without spending gobs of money. A rheostat as far as i can tell on the coil would only affect the amperage but not the voltage.
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An unregulated auto type alt. will put out 16 volts, they can be had 40 to 150 amps
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I’ve had alts where the regulator went bad that did hover around 16-16.5 but i thought it was kind of working. So it wont go past 16 volts?
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Internet search up “Marine three stage voltage regulators”.
There are three different companies making these for the big-live-on-year-around boats.
These boats usually have a largish diesel engine with up to three alternators hung onto it.
The better model of regulator/charge/controllers have allowance to control two separate alternators into different battery banks.
S.U.
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I will try to give 2 cents here…
If the voltage on the field coil of the alternator is not “cut” away the output voltage will rise, even up to 120 V, depending the rpm .
The regulator “senses” the voltage from your battery bank and adjust the current/voltage sending to the field coil, to adjust the output voltage.
A small DIY adjustment :
if you put a small diode between the sense line ( battery to sense input ) it will lower your voltage going to the alternator, this would trick the alternator in thinking that the cutoff voltage is not reached yet and give a slight higher output .
Also: connecting the sense cable to the battery directly, will improve the voltage since it does not gets influenced by the losses in the cable from alternator towards battery. ( in some cases even up to 1 volt )
Deep cycle battery’s , if used for standby, require lower “floating/charging” voltages then battery’s running on cycle duty ( load / unload ) see picture.
Same goes for solar systems…
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Would a rheostat accomplish the same thing?
rheostat to do what ?
a rheostat is just a variable resistor, hand adjusted
a regulator is selfadjusting electronic…
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Can you use one to adjust the resistance of the field coil or the sense wire to trick the regulator?
short version for otherwise a long answer:
http://www.pssurvival.com/ps/Alternator/Alternator_Secrets_2001.pdf
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I think you should explain what kind of a system you are talking about.
To me, it sounds like you have some sort of solar array that is already connected through a charge controller of some sort of a set of batteries.
We don’t know what voltage the battery bank is. All we know is that you need to “keep it under 70-80 volts for a margin of safety”. Did I miss something here?
So, do you simply want to parallel an engine powered generator with your solar array?
Is there a grid tie in the mix?
Your “anywhere from 25-100 volts” answer is a little vague.
I don’t know why you are stuck on the idea of a PMA since you are (apparently) not using wind power.
If you are going to start an engine when you want to charge your batteries, you might as well switch your (solar?) charge controller off.
Since you are already pretty deeply involved in your system, I suggest you take some time to learn some basics about electricity.
I like Koen’s suggestion of adding a (silicon) diode in the sense line of the regulator if you can find it.
You are approaching some possibly very dangerous voltages if you go over about 50 VDC in any part of your system.
So please be careful and “keep one hand in your pocket”, as we used to say.
Thirty years ago if was popular to use a regular automobile alternator to run 120 volt power tools with universal motors. A couple of companies even sold a little box that mounted under the hood to make the conversion. All the kit did was to disconnect the alternator’s output from the car and send it to a normal household duplex receptacle and then to feed full battery voltage directly to the alternator’s field windings (rotor). To use it, one simply revved up the engine until a DC volt meter read about 120 volts and you were good to go. I sawed a lot of lumber out in the woods that way.
My point is that if you fool around with those alternators without knowing for sure what is going on, you can get in trouble fast.
About the “16 volt” discussion. The reason that the guy’s alternator put out 16 volts when its regulator failed is that it’s output was still connected to the car’s battery. If the alternator hadn’t had that load attached, the voltage would have gone up as in the above paragraph.
Many years ago a neighbor stopped by our house complaining that he couldn’t keep the fan belt tight on his Chevy pickup truck. I sensed that something was not right and checked the battery voltage. It was in that same 16 volt range. I told him that he’d better get that fixed right away. He didn’t. A few days later, while waiting at a traffic signal, the truck caught on fire an almost burned to the ground.
Learn Ohm’s law.
Sorry if I sound like a “critical parent”,
Pete Stanaitis
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Sorry I will clarify. I have a spare midnite classic 150. Its a Mppt controller with a max limit of 150 volts. It supports wind/hydro/solar. I do have some electrical knowledge I built my entire system from scratch. Not tooting my own horn but toot toot.
I do want to parallel charge my array with an engine. At this point I may be better off tracking down a proper charger than mess with alternators etc. Fuel efficiency is not as important in a gasifier. I just want to do it right.
I have a 12 volt 1064 AH battery bank. I need at least 55-60 amps to properly charge it. Thats my problem. I’m stuck with dumb chargers that can only bulk but reach the proper 16 volts for equalizing (very few heavy duty chargers exist anymore, especially under 400 dollars) or very dumb smart chargers that charge at 14.4 volts and cut off way to early and lack an equalization option.