Budget alternator derating? how can I do it?

[stormalong]

It is possible that the voltage regulator is only enabled by the control wire that normally goes to the keyswitch and that both the power for the regulator and the voltage sense come off the alternator output connection that goes to the battery.

In that case the voltage level is irrelevant as long as it is above the voltage threshold needed to enable the regulator. Such a design would reduce the current going through the keyswitch - a good thing in most cases. Measure the current flow through the wire to the keyswitch to test my theory. If it is very small than messing with it will have no effect on the output current.

It is also possible that, if the voltage sense is through that keyswich wire that reducing the voltage at that point the regulator reacts by full fielding the rotor, the exact opposite of your desired result.

The PWM control to the rotor is at the output of the regulator, not the input. PWM input to the regulator is irrelevant. Trying to externally control an internal voltage regulator is a waste of time and effort unless you know exactly how that regulator functions.

PS: I have been following this thread since it began. Using a bicycle spoke to control output is a very bad idea. You are adding a resistor of unknown value to the circuit and resistors get hot. Do you really want a heating element operating in your engine space?

[Cheechako]

Originally Posted by Compass790

Yes that's true I could but have to bypass the VR. I was hoping to find a way to control current to rotor magnet & still keep the VR in play but it seems not possible.
Still glad you reminded me of the manual option thanks.
Bit wary of that as I might end up overcharging but guess I can get a high voltage alarm. Also i was fixated on the dimmer & how i could utilise it.

Long thread, i don't know if it's been mentioned... but: what about just putting a large diameter pulley on the alternator? Then when the boat is moving and the engine warmed up, maybe it would work OK robbing less HP.?

[Compass790]

Originally Posted by stormalong

It is possible that the voltage regulator is only enabled by the control wire that normally goes to the keyswitch and that both the power for the regulator and the voltage sense come off the alternator output connection that goes to the battery.

In that case the voltage level is irrelevant as long as it is above the voltage threshold needed to enable the regulator. Such a design would reduce the current going through the keyswitch - a good thing in most cases. Measure the current flow through the wire to the keyswitch to test my theory. If it is very small than messing with it will have no effect on the output current.

It is also possible that, if the voltage sense is through that keyswich wire that reducing the voltage at that point the regulator reacts by full fielding the rotor, the exact opposite of your desired result.

The PWM control to the rotor is at the output of the regulator, not the input. PWM input to the regulator is irrelevant. Trying to externally control an internal voltage regulator is a waste of time and effort unless you know exactly how that regulator functions.

PS: I have been following this thread since it began. Using a bicycle spoke to control output is a very bad idea. You are adding a resistor of unknown value to the circuit and resistors get hot. Do you really want a heating element operating in your engine space?

Thanks for your reply. I need time to mull over it.

The only + wire going to the VR comes from a relay in the instrument panel.
Its soldered to a brush connection & it carries about 3 amp under full load. There is no other wire connected to the VR & brush set except the internal VR button connections. No connection to diode trio or B+.
I intend to take the VR off the alternator & just have a brush set in there & wire the VR & dimmer externally. Cant do any more mods for a week or 2.

The possible solution is evolving as more suggestions come in & I begin to understand more.
I am resistant to the bike spoke as i'd rather twist a dial anyway apart from the other drawbacks.

[Compass790]

Originally Posted by Cheechako

Long thread, i don't know if it's been mentioned... but: what about just putting a large diameter pulley on the alternator? Then when the boat is moving and the engine warmed up, maybe it would work OK robbing less HP.?

Thanks for trying to help.

Yes it has been suggested but I'd rather have a twist dial solution that is variable. i want the lower revs option charging at anchor.
I think you mentioned a rheostat earlier, thats still on the table if I cant get the dimmer to work.
There is a 2 week holdup in testing on this as I have a hand out of action.

[Cheechako]

Originally Posted by Compass790

Thanks for trying to help.

Yes it has been suggested but I'd rather have a twist dial solution that is variable. i want the lower revs option charging at anchor.
I think you mentioned a rheostat earlier, thats still on the table if I cant get the dimmer to work.
There is a 2 week holdup in testing on this as I have a hand out of action.

I thought the rheostat option was ruled out? re: it adjusts voltage but not output or something like that?

[Compass790]

Originally Posted by Cheechako

I thought the rheostat option was ruled out? re: it adjusts voltage but not output or something like that?

Yes well I'm not too sure, there are differing opinions. I think it depends on how alternator is wired for 1 factor but there are more

I'm still fixated on the dimmer & haven't ruled it out yet. I have been informed I wired it wrong 1st up

The twist dial is possible as is evidenced by this listing:https://www.ebay.com/itm/ALTERNATOR-...Cclp%3A2334524

Just that I want to make my own for peanuts in cash but a fortune in hours. lol.

[Wotname]

Originally Posted by Compass790

Yes well I'm not too sure, there are differing opinions. I think it depends on how alternator is wired for 1 factor but there are more
.........

If you chuck away the VR and use a suitably sized rheostat wired in series with the rotor winding, you will control the output just fine. The only downside is that the output control is purely manual and you will need to adjust the rheostat as required.

[RaymondR]

Originally Posted by Wotname

If you chuck away the VR and use a suitably sized rheostat wired in series with the rotor winding, you will control the output just fine. The only downside is that the output control is purely manual and you will need to adjust the rheostat as required.

The problem with many of these solutions which bypass the regulator is that you run the risk of destroying the battery if you forget to carefully manage the alternator output voltage. I well know this from expensive personal experience.

The advantages of managing the alternator output by increasing the resistance of the charge circuit are that you retain the protections which the regulator provides and battery charging will still occur but at a slower rate.

Mucking about with the voltage regulation function can have some very serious consequences.

[Compass790]

Originally Posted by Wotname

If you chuck away the VR and use a suitably sized rheostat wired in series with the rotor winding, you will control the output just fine. The only downside is that the output control is purely manual and you will need to adjust the rheostat as required.

Thanks Wotname,
Yes the rheostat is still on the table but I wont be chucking away the VR. I'll try & find a way to switch from rheostat circuit to VR as required.
IF I cant make the dimmer work.

[Compass790]

Originally Posted by RaymondR

The problem with many of these solutions which bypass the regulator is that you run the risk of destroying the battery if you forget to carefully manage the alternator output voltage. I well know this from expensive personal experience.

The advantages of managing the alternator output by increasing the resistance of the charge circuit are that you retain the protections which the regulator provides and battery charging will still occur but at a slower rate.

Mucking about with the voltage regulation function can have some very serious consequences.

Yes I'm alert to this problem thanks Raymond. My late uncle boiled his batteries dry with manual alternator control. He put a timer on later.
We used that idea when we had diodes in the sense wire to convert our 14v reg into a 14.5.

Appreciate the warning tho.

[Sternwake]

I have a bunch of 8 amp PWM LED dimmers that I have removed from the task of dimming lights, or speed controlling fans

If I remember correctly the (-) output wire has the PWM signal on it.

Put your digital multimeter on the input +, and the output -, and see if the ouput voltage changes when twisting the potentiometer.

I'm pretty sure mine have continuity between both in and out + when hooked to nothing. I will recheck tomorrow.


One thing about my PWm LED Dimmers, on LEDs is they would only dim to a certain amount, then shut off. Still a bit brighter than I liked sometimes, then off completely.

All these 13khz 8 amp LED dimmers would have the led bulbs whine audibly, when dimmed, some bulbs worse than others need to get 21khz or higher for a young person to not be able to hear it when dimmed

I now use 5 amp voltage buckers with a XL4005 or XL4015 chipset. 150khz. These buckers allows me to dim the LEDs to barely visible pinpoints of light. without any audible( to me) whining. But the LEDs shut off around 8 volts. Some fans are as low as 3v. I suspect you want to go even lower for your field.
I think the XL4005 chipset is rated to buck to a lower voltage than the XL4015,.
The xl4005 bucker loses 0.27v across it turned all the way up. 12.0 in 11.73 out max @ ~3 amps.
The XL4015 based bucker loses 0.19V across it, 12.0 in 11.81v out max @ ~3 amps

As I said when I collected some field current data on my Transpo voltage regulator, the voltmeter with both sense and power on leads twisted together and touching the filed output+, does not even come on until 3.5 ro 4 v.

I applied at least 20 additional amps of DC load on the DC system before field output+ voltage climbed enough to even light up the voltmeter.

This is on a small frame automotive alternator with a 50 amp rating at idle and 120 amps max.


Check to see if the output (-) on your PWM dimmer is Pulsed, rather than the (+).

I wouldn't know how to get around that on the field + wire.

Perhaps place dimmer inbetween alternator frame ground to one of the brushes instead of on the field (+) of the other brush.

YOur dimmer might be best off dimming and a bucker or perhaps buck/boost converter can accomplish your goal.

[Compass790]

Thanks sternwake,
Yes you are correct the PWM part of the dimmer is on the -
I have got a possible way to wire the circuit using dummy brush set & the the VR being off the alternator.

Have only tried the dimmer with an incandescent bulb & it works good.

Trust me, any squealing wont be an issue. Our single banger YSM8 may be puny in hp but it puts out a lot of noise & vibration.
The VHF & phones are unusable when engine is running. I always wear earplugs in the cabin.

I'll attach my 2nd attempt at a wiring diagram with external VR.

This will have to be trialled as I don't know enough to say it will work.

[thinwater]

55 amps ~ 770W = 1 hp.


That is something out of 7hp, but if it only happens when the battery is flat, is it a big deal? Do you run WOT that often?

If I did swap in a smaller alternator or permanently derate it, I would add solar, since 10 amp for an hour or two each day isn't doing any changing that matters to a cruiser.

Summary. If you day sail and marina hop, it hardly matters since the boat is plugged in and the battery is always nearly full. The alternator won't be puting out 55 amps, but a 10 amp alternator would work fine. If you cruise, you either need the 55 amps or you need to add solar.

I've cruised with a pair of 10 amp alternators (cat powered by outboards) and unless you motor all day, which sucks, they don't add much.

[lateral]

Originally Posted by thinwater

55 amps ~ 770W = 1 hp.


That is something out of 7hp, but if it only happens when the battery is flat, is it a big deal? Do you run WOT that often?

If I did swap in a smaller alternator or permanently derate it, I would add solar, since 10 amp for an hour or two each day isn't doing any changing that matters to a cruiser.

Summary. If you day sail and marina hop, it hardly matters since the boat is plugged in and the battery is always nearly full. The alternator won't be puting out 55 amps, but a 10 amp alternator would work fine. If you cruise, you either need the 55 amps or you need to add solar.

I've cruised with a pair of 10 amp alternators (cat powered by outboards) and unless you motor all day, which sucks, they don't add much.

More like 2hp with inefficiency.Very relevant imo.
I have spent all my time in other direction ditching a 55A hitachi and getting a very similar bosch to deliver sustained 80+ A.
But I guess 10A is better than no amps on a sustained motor. At least it would keep the autopilot, electronics and fridge fed.
Great thread. Refresher on alternator 101. Thanks to all the contributors that shared their work arounds. Brilliant!

[Compass790]

[QUOTE=thinwater;3241956]55 amps ~ 770W = 1 hp.


That is something out of 7hp, but if it only happens when the battery is flat, is it a big deal? Do you run WOT that often?

If I did swap in a smaller alternator or permanently derate it, I would add solar, since 10 amp for an hour or two each day isn't doing any changing that matters to a cruiser.

Summary. If you day sail and marina hop, it hardly matters since the boat is plugged in and the battery is always nearly full. The alternator won't be puting out 55 amps, but a 10 amp alternator would work fine. If you cruise, you either need the 55 amps or you need to add solar.




Thanks thinwater,
Yes what you say is true but...

I know this is an extremely long thread but we do have solar & our usual power usage is 55amps in 24 hrs. Only run, GPS, Engel & a few LEDS.

We live & cruise on it fishing & diving up to 10wks at a time.
Guess you are right 10 amps is not a huge amount to get but very ocaissonally we might have to motor all day, usually they are sunny ones so it's not an issue & we can turn the 55amp alternator off.
I dislike alternator charging at anchor, if you heard & felt the yanmar ysm8 you would instantly understand.

We are always effectively at WOT once warmed up as we are overpropped.
Yes that needs to be fixed.... Its on the list.
I thought any battery charging help is better than none & it is an interesting project that that I could do for peanuts in $$ terms.
In other words I'm amusing myself & learning about the electrical system at the same time.
Nice to have knowledge of boat systems when you are distant from expert help.