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Old 19-03-2016, 09:51   #16
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Re: Using a common automotive alternator with external regulation

Originally Posted by jimbunyard View Post
My vote is for a Delco 10SI or 12SI alternator. Have been using them for 30+ years, they're robust, simple and can be rebuilt with no soldering on your kitchen table in about 30 minutes with 2 nut drivers and, if you need to replace the front bearing, an allen key and a 15/16" wrench. Plus a fairly complete rebuild kit with bearings can be had for less that 20.00...
I agree, make the effort to learn to repair the delco si10 or si12 and your problems are over. The si12 is capable of higher output because it cools itself better. You can build to what ever specs you want. The other delcos are also options but I'm not familiar with them. You could probably go to an auto parts store and ask for an alternator for a 1984 chevy ck10 and get a new si12 with a lifetime warranty for $60.00.

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Old 19-03-2016, 10:12   #17
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Re: Using a common automotive alternator with external regulation

Originally Posted by svadagio View Post
I have 2 2800JB LN alt. Both were bought internal reg. The local alt rebuilder simply opened them up and added a wire inside. That is all that is needed. He said any alt can be changed. Try going to a place that rebuilds alt for cars. I assume you have that down under.

SPOT-ON the rebuilder. I have two 2.5kw 2-V alternators. It would be a fortune to replace but only 60 bucks to replace all the brushes & diodes. At this price, I won't open them myself. Twice hit by lightening. Each time blew 14 diodes out of one of these. Most re-builders have ready stock to sell and will be able to alter to operate on an external controller.

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Old 19-03-2016, 13:46   #18
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Re: Using a common automotive alternator with external regulation

I have always used auto alternators of various makes and never had a problem when using lead acid batteries. I size the alternator at 25-30% of batt amp hours. The only time you are going to get near max output is motoring hard with a low batt as you need the alternator running at high revs before you get high output. If you have a high revving turbo engine and/or batt that have very high charge acceptance there can be issues but easily resolved by reducing revs. Remember all alternators need a good air flow, if it is jammed into the corner of a tight engine compartment you may have problems with any alternator including the large frame 'rated' ones.
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Old 19-03-2016, 13:53   #19
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Re: Using a common automotive alternator with external regulation

I deeply cycle a group27 Northstar AGM in my Vehicle with an upgraded charge circuit. The alternator is a Chrysler 50/120 externally regulated model. The problem is the voltage regulator is internal to engine computer, and it decides either 14.9v, or 13.7v is fine and dandy, with apparently no regard to logic or reason. 13.7v when the battery is still depleted is infuriating, 14.9v held when I know the battery is full is frustrating. Sometimes it would choose 14.1v, just to irritate me.

If one tries to bypass the ECM's regulator, one gets an illuminated check engine light. Can't pass a California smog test with an illuminated CEL.

I found one outfit claiming to have a 'trick the ECM' device that will keep the CEL off. I bought it and it is a simple 50 watt 10 OHM resistor. It works, but does get very hot. I thermal epoxied a larger finned heat sink to it.

For an external voltage regulator, I picked up a Transpo F540HD originally designed for a Ford for 25$. It has a 2K ohm potentiometer inside it for adjusting voltage.

I bought a 2K ohm Bourns 10 turn potentiometer with counting dial, Depotted and removed the mini voltage pot in the 540HD, soldered wires to its legs. I mounted the Pot on the dashboard next to my digital voltmeters.

I grounded one field terminal on the alternator to its own casing, and ran a 12 awg wire to the F terminal of the 540HD VR. I soldered a ring terminal to the casing of the VR and ran 10AWG to the casing of the alternator. I found a dedicated wire under my dashboard live only with the engine running and ran this to the S terminal. The A terminal, always on, should go right to battery(+), but I cheated and put it on the (+) output stud on alternator. I also put a K type thermocouple in with this new wire harness and thermal epoxied the probe to the alternator casing. The 4th VR terminal, the I terminal is for the Idiot light. I did not use this terminal.

Now I can choose any voltage between 12.8v and 15v from the driver's seat.

The Transpo 540HD gets warm. I added another finned heatsink to its backside.

There is some voltage sag at hot idle, upto 0.3v. My gas engine idles at 525 rpm when hot, so this was expected.
The dial indicator on the bourns potentiometer is not super repeatable, depending on the state of charge of the battery. One full turn equates to about 0.3v difference.

Idle speeds give it the most issues. At Idle, I can compensate for the sagging voltage by twisting the pot upward, but then of course at higher rpms when moving, it overshoots the voltage. So mostly I don't bother as with this TPPL AGM there is not too much difference in Amp flow at 14.1v vs 14.4v, and redlights only last so long.

I do crank it way down to 13.0v on some cold starts with a depleted battery and let the engine oil warm up some before cranking it upto 14.5v and allowing 60+ amps to flow.

The check engine light stays off unless I crank voltage above 14.7v. But it goes out on the next restart. The battery is not inside engine compartment or subjected to its heat.

The temp sensor on my alternator has proven interesting. With ~50 amps total output is registered 119F while moving 25 to 40MPH. Then, when parked and idling making 32 amps total, temp shot upto 139f.

Parked, hot idling and maxed out with lights Blower motor and everything else on making around 45 to 50 amps, within 30 seconds temp had risen to 160F.

The combination of a moving vehicle, and higher rpms on the alternator nearly instantly have the temperature drop, and idling at a redlight has the temperature increase rapidly when the battery is depleted, and more slowly but still by 10 to 15F when the battery only needs 15 to 20 amps to be held at 14.5v.

As expected, but actual data confirming my suspicions was nice.

The 10 ohm 50 watt 'trick the ECM' resistor visible in background

I ran the twisted leads for the remote potentiometer through a ferrite and anti chafe sleeve, and used 'amazing goop' as stress relief.

I've only measured a 6.2 amp field current maximum, at this point.

I can return the original ECM's voltage regulator to duty quite easily in the event of failure. Or just acquire a backup Transpo F 540HD for 25$.

I am very happy with the modification. The only issue is the 0.3v voltage sag at hot idle speeds, and this 'might' be mitigated somewhat if I were to actually hook the VR's A terminal to the battery instead of the ALT(+) stud.

Of course it is a manual system too. Nothing Automatic here, but my personal preference is manual voltage control on all my charging sources.

This inexpensive transpo voltage regulator could be good to have onboard as a backup in the event of a failure at sea.
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Old 19-03-2016, 13:59   #20
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Re: Using a common automotive alternator with external regulation

Only if your boat is diesel. Auto alternators are not ignition protected. If it is. Go for it.
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Old 19-03-2016, 17:24   #21
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Re: Using a common automotive alternator with external regulation

The most important thing you posted is "AGM". Whatever alternator you choose must charge bulk and absorption at no higher than 14.4V and float no higher than 13.3V or you will ruin your batteries.

Most stock auto and truck alternators charge at voltages that will cook your batteries. External regulation is essential. My electrician told me that many common auto and truck alternators can't be converted to external regulation owing to the newer design where the brushes and regulator are all in an impenetrable block of circuitry. He couldn't, for example, modify my Hitachi alternator for me.

For what it is worth, I am THRILLED with the Balmar alternators and external regulators I chose when I switched to AGM. And I love the AGM's too. They really accept charge quickly.
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Old 19-03-2016, 19:42   #22
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Re: Using a common automotive alternator with external regulation

I see you've got plenty of replies on this, here's what I use on my Yanmar 3GM30F powered boat.
DB electrical, DB Electrical - YANMAR MARINE DIESEL ALTERNATOR 3JH2 3JH3 4JH2 4JH3 4LH 6LY KBW20 this alternator is 80 amp, runs off the standard belt/ mounting .
With that, I use a Sterling Pro Reg D remote regulator to charge the 4 T105 house batteries plus the 660cca engine battery. Follow the Sterling instructions to determine which brush to solder the lead to (you have to split the alternator and solder the 10AWG wire to a brush) and it then regulates the alternator; leaving the original regulator in place, it will automatically default to that if the Sterling fails. Don't be afraid of calling Sterling for help, if you need to. they are very responsive. ....easy peasy, done!
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Old 20-03-2016, 02:12   #23
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Re: Using a common automotive alternator with external regulation

Thanks everyone for your input. I understand that auto alternators have limited duty cycles and suffer from heat, but then again the standard alternator on my motor is basically an automotive type with what I consider a design fault in that the regulator has exposed one amp diodes in the air cooling stream which quickly corrode so, imo, just about anything else would be better anyway.

But I do want to externally regulate to protect the AGM's as long periods of motoring concerns me with regard to the charging circuit.

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Old 20-03-2016, 02:28   #24
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Re: Using a common automotive alternator with external regulation

Greetings and welcome aboard the CF, lorenzoj.
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 20-03-2016, 04:35   #25
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Re: Using a common automotive alternator with external regulation

On our Perkins 4108 m we have the old standard Lucas alternator.
In 2000 the external Bosch regulator ( Yes dinosaur ) died.
Could not find a replacement so I made a bulb / switch regulator myself.
I regulate the field current by switching simple 12V light bulbs into the line.
All switches up means “Full power”. The anchor coils gets what ever tension we have on the system ( Battery's ) That means full output. Flipping switches down connects first one light bulb, then two and finely a washing machine rheostat in line with the anchor. That way I can regulate myself how much output the alternator gives.
All switches down means no power to the anchor, The alternator just idles.
Regulating this way is not foolproof ! !!
I have two big voltmeters witch I constantly monitor. One inside, one ouside. Batt´s reaching 14.5 V I start regulating down.

In fact the alternator is very seldom used. We have enough solar and wind to cope with all needs.
On repeating days without sun or wind I can charge our battery´s in a more clever way than any automatic system can do.
I know what weather we will have the next days, I know what electrical power we will need, I know if the engine will be running or not. I know when new batt´s will be bought. No regulator knows parameters like that.

Most regulators turn power down to a trickle if 14,1 V is reached. Way to soon.

If I forget to regulate down I have a problem.
Happened once in 16 years of cruising. Lee shore, big winds coming up, old battery´s ( Could not take a lot of charge ) and general confusion made me forget the charging. When the anchor was finally up ( hand operated winch ) and I was under way some 20 minutes later there was already 32 Volts on the system. This fried my solar regulator.

If I stop the engine and forget to cut the power to the alternator anchor it pull´s 4 to 5 Amps.
No harm done but a big draw like that is noticed. Forgot it a few times, even over night, no damage done.

Some say that letting an alternator run without power will ruin the brushes.
Still the second set of brushes after all those years. Old ones just changed because I changed the alternator bearings.

In case of smaller engines, don't under estimate the power taken by a charging alternator.

Not suggesting this is a good idea for anyone, I like my system
Low tech, never fails, costs nothing. Not even dummy proof.
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Old 20-03-2016, 07:14   #26
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Re: Using a common automotive alternator with external regulation

Mid 80's 65 amp inturnal reg GM less than 50. Bucks at orilies same Mount Ting as Motorola.
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Old 20-03-2016, 08:23   #27
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Re: Using a common automotive alternator with external regulation

Originally Posted by Nanamuk View Post
I bought 3 Bosch 85 amp alternators in Darwin - wanted spares that could be swapped with no need to change belts or mount arms - they have a very open body, you can buy an easily installed clip to change to external regulation and are inexpensive at an automotive parts store. That was in 1999 and the 1st one is still working after the completion of our trip back home to B.C. Canada.
I standardised on these years ago and have never burnt one out, they are cheap and easy to find spares for in Australia.

The regulator removes with two screws and can be replaced with brush only units if you want to use an external regulator. Alternatively you can just solder a wire to the brush terminal inside the alternator.

I have current boosted them by putting forward biased diodes in the battery voltage sense line.

I have current limited them when using them on house banks for contingency charging by putting a bike spoke in the output line and sliding one of the leads along until the required output is found. You need to place the spoke where it can air cool and not set anything ablaze, it will get pretty hot.

I pretty well always put five watt resisters in the battery sense and lamp lines, prevents zapping the regulator if you get them mixed up.

I am what might be called an alternator abuser so prefer to use cheap, readily available units and carry lots of spares.
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Old 26-03-2016, 13:11   #28
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Re: Using a common automotive alternator with external regulation

Buy two
Treat them with lacquer
Choose models with in-built (not outer) fan
serpentine is OVerly expensive....
Buy extra power, and accept a lower performance...

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