Budget alternator derating? how can I do it?

[Compass790]

Originally Posted by RaymondR

The OP was looking for a way to decrease the output a fixed amount to take the alternator load off the engine and there's no more practicable nor inexpensive way to do so than the bike spoke resister in series with the alternator feed to the battery. You adjust the amount of spoke in the circuit until you get the required reduction then clamp the connections. I have cut the spoke to length and used crimp connectors.

A double pole double throw switch would let you switch the DIY resister into and out of the circuit or if you wanted it to drop out when the ignition switch was turned of you could use a latching circuit using a double pole double throw relay. All simple, effective and cheap and does not require any interference with the normal charge circuit and would do exactly what the OP required.

I've been an enthusiastic admirer of Rube Goldberg all me life mate.

I'm a Rube Goldberg enthusiast too cobber & I get the bike spoke method ,just like the field wire method better.
Enjoying the interplay between the experts tho Wotname appears to have sheathed his sword.
Maybe he's waiting till I fall on mine
Wouldn't be the first time nor will it be the last but hey I'm having fun.

[Compass790]

Originally Posted by kenbo

While what you suggest will reduce the output of the alternator it is not the only way to achieve lower output or the optimal way. Fooling the VR into thinking the battery is at a higher state of charge than it is a terrible practice for battery health.

A better method is to introduce resistance into the rotor's field coil circuit. This resistance can be static or variable. The OP is looking for a variable solution. In this way, the alternator's charging parameters are unchanged but it's output is reduced.

Yeeess this will be my approach & I agree. I dont know enough to argue the case but I'm glad you guys are chiming in

[belizesailor]

Originally Posted by kenbo

Raymond you do realize that the voltage drop across the resistor, I mean spoke, that you've inserted into the Bat+ lead to the battery does effect the batteries ability to be properly charged. So you have in effect altered the normal charge circuit.



By varying the current going through the rotor by inserting a rheostat in series to one of the brushes, you do not alter the Vset of the voltage regulator and only reduce the amount of power the alternator can produce. The battery will charge with the correct voltage regulation but with reduced current.

As kenbo points out, an advantage to the variable resistor approach is that it is by definition VARIABLE. This means you can derate when underway to provide more propulsion power and then crank it up again when not underway for more charge capacity. However, there is a down side...

This method is fully manual, YOU must monitor the charge state and adjust the variable resistor accordingly.

[Sternwake]

The modified manually adjustable voltage regulator that I use, with a remote 10 turn potentiometer, changes the target voltage, which changes the amperage the batteries will accept. But DC loads other than the depleted battery, will mostly remain the same degree of DC load, regardless of voltage chosen.

With well depleted batteries I can dial in as little amperage from alternator to battery, to its maximum at the flick of a wrist( well several subsequent flicks) and can dial in just over 15.3v if desired and can go down to 12.0v as well, perhaps lower, I've never tried, honestly.

but a 30 amp electrical load other than a depleted battery, is still going to be an approximate 30 amp load regardless of whether I choose 3v above, or just 0.05v above battery voltage by twisting the adjustable VR's voltage potentiometer.

Put a hall effect sensor ammeter on the feed into battery next to the remote potentiometer. twist dial to achieve intended amperage into battery, from cockpit, no climbing below to adjust a collar on a SS bike spoke.

While I have a ten turn pot for changing voltage, I find the ~ 5 to 6 full turns required to go from 14.7 down to 12.7 to be annoyingly precise, and would prefer a 1 turn potentiometer, but its probably better for the voltage regulator to change target voltage more slowly, and I generally only go from 13.6 to 14.7 and back which is about 2.5 wrist flicks.

I have put amp and volt meters on VR input and field output to satisfy my curiosity.

The voltmeter I used on field wire only comes on above ~ 4.2 volts. With fully charged battery I needed to add significant load before I could get voltmeter on field wire to turn on. I did not fully explore the data accumulation possibilities, when I had the meters in place. It was a quiet day and my battery was already full and my curiosity was mostly satiated regarding field output and how it related to alternator output and I've not bothered to set the meters back up since.

As the OP knows there are many ways to skin this cat. I effectively do the same thing with a 25$ VR and a 6$ 10 turn trim pot. The voltmeter and ammeters were already in place so i could watch the response to flicking my wrist while underway. With a thermocouple on battery and alternator, voltmeters and ammeter, I manually adjust voltage to properly feed battery according to my desires.
It was once rocket surgery to me, but now I look back and call my former self an idiot.

The ONly issues with my system, is that it appears the 10 turn 2k Ohm Bourns potentiometer, which could be a counterfeit, sometimes develops flat spots and spikes resistance wise. The cure seems to be, with engine off, to turn teh know through its full range once or thrice.

I used to have a turns counter on the 10 turn bourns pot, but found I never bothered to look at the counter, and removed it to lessen the height of the knob.

[Compass790]

thanks Sternwake,
If my setup works I will post details/pics as you might like my dimmer as its maybe 130o turn frm 0 to 99% & cost about $2 US.
I intend to use it by finding out how many amps ( on clampmeter) I can pump out of the alternator at our cruising speed before over-fuelling condition & then marking the dimmer dial.
I believe the fridge kicking in will have no effect if I'm controlling the field current but I don't have enough knowledge to be sure of that.
The beauty of CF is mostly someone will chime in to help.
My guess from rough calc of load vs hp production of motor is 8-10 amps.
Of course I realize there is no free lunch & we would attain maybe 200rpm lower with alternator on but thats the tradeoff.
I realise dirty btm or headwind/sea will alter the max amps we can produce but we usually sail when we have wind. Even if its cloudy we still get 4 amps out of the solar & if we can add as little as 8 amps from the alternator it will be a lot better to keep our fridge going & batteries long lived.
The fitted VR will still be in play so I wont risk overcharging AFAIK.
Enjoying your posts & like the way you are thinking.

[Compass790]

Well Cruisers,
I will post a couple of pics of the wiring for y'all to critique or suggest improvements. Tried again last Mon. but dimmer had no effect. Think that its because I gave it a path to earth thru the voltage regulator but it needs to go back thru the dimmer. The VR is an N-type. The dimmer has connection between the + terminals with no wires connected.
I should have posted wiring pic in first post but had 'puter/phone problems.
The pic where it says N-type is the one I've tried.
The other one with the VR in parallel with a switch is a possible variation.
I'm at my 1/2 wits end.
Well not really as there is still the bike spoke & rheostat
Any suggestions gratefully received.

[lateral]

Limiting the current with resistance in field circuit is inefficient and crude.

You are limited imo by the internal regulator designed to control output by sense voltage.
I would try a DC/DC buck converter to incrementally increase the voltage on the sense wire and let the internal regulator do its thing, work with the design of the original.
In series, from bat to sense terminal.

[RaymondR]

Originally Posted by lateral

Limiting the current with resistance in field circuit is inefficient and crude.

You are limited imo by the internal regulator designed to control output by sense voltage.
I would try a DC/DC buck converter to incrementally increase the voltage on the sense wire and let the internal regulator do its thing, work with the design of the original.
In series, from bat to sense terminal.

Well there you go, "inefficient and crude" maybe but it's still actually the elegant solution from an electrical engineering viewpoint.

A $0.3 bike spoke and maybe a $20 double throw single pole, make before break switch. Once set always forget and does not require any adjustment in service. Practically fool proof (I say practically because a very wise engineer warned me many years ago to give up trying to design fool proof because in his experience fools were really ingenious bastards) and does not require any messing about in the internals of the alternator. What's not to like?

[lateral]

Originally Posted by RaymondR

Well there you go, "inefficient and crude" maybe but it's still actually the elegant solution from an electrical engineering viewpoint.

A $0.3 bike spoke and maybe a $20 double throw single pole, make before break switch. Once set always forget and does not require any adjustment in service. Practically fool proof (I say practically because a very wise engineer warned me many years ago to give up trying to design fool proof because in his experience fools were really ingenious bastards) and does not require any messing about in the internals of the alternator. What's not to like?

Whatever works and can be replaced at sea is ok with me.
At least you have proved it works, more than I can say with upping the sense circuit voltage as I have the opposite need.
Actually, love being able use something simple for other than its original use.

The buck is $7.50 and the sense wire is external so can't see a problem with that install. Similar to this
https://www.surplustronics.co.nz/pro...er-buck-boost-
Can't say I've done it though and there is the possibility it won't derate the alt enough as it depends on the VR scaling.

[Compass790]

Thanks RayR & Lateral,
Yes RayR the bike spoke is where I may end up but I'm pig-headed & want to try the dimmer. What I really need help with is the wiring but I can say my 2 wiring diagrams are both crap, at least the VR wont function wired like that. I've made a brush set up now with no VR connected & wires leading off the brushes & will try the dimmer alone & then try adding the VR off the alternator later. Wont try posting a wiring diagram again until I get help from someone who knows how to draw one & actually knows more about whats happening.
Thanks in advance Wotname if you can help with that

Yea Lateral the buck converter is another possibility but again still trying to find a way to make dimmer work. Just need to figure out the wiring. Dimmer should work,its a PWM & so is the VR AFAIK. Just the installer doesn't know what he is doing.

Will be a delay in more experiments as I'm having a hand op so might be a few weeks before I can play again.

[Wotname]

Originally Posted by Compass790

Thanks RayR & Lateral,
Yes RayR the bike spoke is where I may end up but I'm pig-headed & want to try the dimmer. What I really need help with is the wiring but I can say my 2 wiring diagrams are both crap, at least the VR wont function wired like that. I've made a brush set up now with no VR connected & wires leading off the brushes & will try the dimmer alone & then try adding the VR off the alternator later. Wont try posting a wiring diagram again until I get help from someone who knows how to draw one & actually knows more about whats happening.
Thanks in advance Wotname if you can help with that

Yea Lateral the buck converter is another possibility but again still trying to find a way to make dimmer work. Just need to figure out the wiring. Dimmer should work,its a PWM & so is the VR AFAIK. Just the installer doesn't know what he is doing.

Will be a delay in more experiments as I'm having a hand op so might be a few weeks before I can play again.

Wottie wades in again .

Now you have the existing VR removed and in your hands, how many external connections does it have?

Clearly it will have a ground connection, a brush connection and a 12V supply (or excite) connection but does it have any more? Hint, I trying to ascertain if it has a seperate sense connection or if that is an internal connection (i.e. inside the encapsulated housing).

[lateral]

Does it look like this or have a square black box with wires to reg?
If it looks like this sense is internal from B+.
If black box its external, both have brushes incorporated IIRCly.
As RR said easiest is to control stator current with resistance but thing is you dont know
what the reg will do once you do that, as soon as you put an external load on batteries
you will get a volt drop in sense and VR will try and compensate & stall your motor again.
Better off by far tricking the VR by the sense to a stable voltage.
M2CW

ps Bin the dimmer before the horse dies.

[Compass790]

Originally Posted by lateral

Does it look like this or have a square black box with wires to reg?
If it looks like this sense is internal from B+.
If black box its external, both have brushes incorporated IIRCly.
As RR said easiest is to control stator current with resistance but thing is you dont know
what the reg will do once you do that, as soon as you put an external load on batteries
you will get a volt drop in sense and VR will try and compensate & stall your motor again.
Better off by far tricking the VR by the sense to a stable voltage.
M2CW

ps Bin the dimmer before the horse dies.

Yes it looks exactly like the VR except there is a wire going to the + brush on the VR from a relay in the instrument panel. There is no other connection to the VR inside the alternator. I.e. no feed from the diode bridge.
There is no connection to the B+ on the VR so its sense must be from the +brush wire.
This is a custom setup.
It also lacks that condensor? that is attached to B+ terminal.

I'm gunna flog that dead horse one more time
In maybe 2 weeks. My thinking is the VR is wide open i.e. not chopping up the current into smaller pulses until the setpoint is reached & if I'm controlling the current with the dimmer it wont get to that setpoint.
The dimmer is already chopping the current up into smaller pulses so unless the VR can join them up again ( Hey free energy) it should work.
Maybe my thinking is completely wrong but I wont be happy till I've exhausted all the possibilities.
But as I said I'm going to try the dimmer alone first.
Look on the bright side, you can laugh at my charging at windmills.

[Maine Sail]

Originally Posted by Compass790

I've never tread carefully & ya cant teach an old dog new tricks!

Yes I got that you say I cant control the output current but I still havent received an explanation as to why reducing the current to the rotor doesnt change the stators output. Or maybe I have got an explanation & i didnt grasp it

Because you’d need to use pulse width modulation in order to do this...

[Compass790]

Originally Posted by Maine Sail

Because you’d need to use pulse width modulation in order to do this...

Isn't PWM how a dimmer works?
I'm not being funny I just dont know.
this is what I am going to use.
https://www.aliexpress.com/item/3287...archweb201603_