Budget alternator derating? how can I do it?

[Bittern]

Hello. We use a Spa Creek voltage regulator by-pass, by Weems and Plath on our 55 amp. Paris-Rhone alternator (engine Volvo 2002). It cost about $150 Canadian several years ago. Has over-charge cut-off, and output can be dialed and observed on a built-in analogue meter. Best regards, Peter

[stormalong]

Originally Posted by Cheechako

There used to be a device that was just a big rheostat to control your alternator. The problem with them is you could pound too much in your battery even though it was overheated. I think it was sold by Cruising Equipment Company or some name like that.
I guess it just controlled the voltage sensing to the Alternator...?
Seems you could put a switch in to allow "manual control" with the rheostat (no regulator at all), or switch back to the normal regulator.

It was called a MAC: Manual Alternator Controller, from Spa Creek. Now long gone. Later versions had a timer built into them so you could automatically shut it down. Those things are very dangerous. They can burn up an alternator by overdriving it.

[Compass790]

Originally Posted by RaymondR

The bike spoke acts as a variable resistor. If you increase the resistance on the B+ wire the voltage seen by the regulator will increase and it will wind back the excitation and lower the output amps. I do it when I need to charge the house batteries using the engine alternator so that I don't burn out the alternator.

A SS bike spoke will cost you about 50 cents. Cut the B+ wire, strip about 1 1/2" of insulation and wind each one around the bike spoke. You then slide the wires back and forward along the spoke until you get the amps where you want them. Be careful as the spoke will get very hot at high amps.

Once you have got the right output amps you can wire a switch in parallel to short out the bike spoke resister to get full amps from the alternator.

These things ain't rocket science.

Thanks for the further explanation, you are the closest to my budget so far
It might not be rocket science to you but I did say I had very limited electrical knowledge or understanding in OP
Sorry if trying to make a dummy understand makes you feel like this
The jury is still out as to which way I'll try, will post back when I do but may not be for some time.
Thanks to the community for all the ideas & education.

[Compass790]

Originally Posted by Wotname

Where does the field wire go to - the key switch or the charge light? I will assume it is going to the charge light in which case you are SOOL as your alternator is presently internally sensed and internally excited.

However if it goes to battery +ve via the key switch then likely the alternator is externally excited which means you can disable the alternator by putting a switch in this wire.

Rather than derate the alternator to 10 A, you will be derating it to 0 A but it's cheap .

The problem you have trying to derate an alternator to a set current is that you have no control over the output current, you only have control over the output voltage. Even if you control the output to say 12.5V, as soon as you turn on some loads that say draws a total of 20A, the regulator will crank up the field current until rotor field is strong enough for the stator to supply 20A at 12.5V.

It is called a voltage regulator not a current regulator. The name is the give away.

Ok Wottie,
I naively assumed that limiting the current to the rotor via dimmer would diminish the electromagnet field strength thereby decreasing the current output of the alternator. I wasnt considering the voltage. Am I missing something? ( apart from sufficient brain cells lol)
I was thinking of it as a current regulator.

[Cheechako]

Originally Posted by Compass790

Ah yes forgot to explain maybe that i want the full output if we need to charge at anchor, just want to reduce hp draw when we are motoring.
Haven't heard of a 10amp alternator which is about what I suspect we need to derate to.

Just use the rheostat/switch option.

[Stu Jackson]

Originally Posted by Compass790

Ok interesting idea thanks.

Except the AutoMac, which is what it was called, was not able to reduce output, only increase it.





Either turn your field wire circuit (i.e., ignition) off when you need the power, or get an external regulator. You will turn off your hour meter if it is in the tach, too.

[smac999]

There is no feild wire on an internal regulated alt. Hence the word internal....

There will either be an ignition / excite wire. This makes the alternator the start up. Once the alt is running. Cutting it will Likely do nothing as it will now be self powered. Nor would adjusting its voltage.

Could be a lamp warming light. Sometimes the lamp wire is also the excite wire.

Could be an external voltage sense. Putting a resistor in this line would INCrease the alternator. You’d have to increase the voltage on this wire to make the alt lower. Which would require something electrical.

The only proper way is modiflied the alt for ext reg. And adding an ext reg.

Or stop charging the house bank like in my post.

Stop listening to idiots telling you to put bike spokes in your alternator wire.

[Cheechako]

Originally Posted by smac999

There is no feild wire on an internal regulated alt. Hence the word internal....

There will either be an ignition / excite wire. This makes the alternator the start up. Once the alt is running. Cutting it will Likely do nothing as it will now be self powered. Nor would adjusting its voltage.

Could be a lamp warming light. Sometimes the lamp wire is also the excite wire.

Could be an external voltage sense. Putting a resistor in this line would INCrease the alternator. You’d have to increase the voltage on this wire to make the alt lower. Which would require something electrical.

The only proper way is modiflied the alt for ext reg. And adding an ext reg.

Or stop charging the house bank like in my post.

Stop listening to idiots telling you to put bike spokes in your alternator wire.

He says he did put a switch in to turn it off.... I wonder where if no field wire? Isn't a Field connection and Excite the same thing? A regulator, internal or external, must get it's info from some connection..? But yeah, the field reads battery level, a lower voltage will increase the output I suppose. He needs to decrease output... hmmm
It's a conundrum with limited Hp. I think he's stuck charging in neutral...

[lateral]

Actually Wotname got me thinking (phew). Dave cheap ($28) VR is not a help. I don't think lowering the output voltage is going to be your solution. Especially if you have inductive loads. Resistive yes, but not enough to help you and not create other problems.
I have only ever been trying to do the opposite.

And the rotor is an inductive load as well so controlling the current in that via the field wire will require electrotrickery, perhaps fooling the sense wire circuit that battery voltage is way higher than it is. Please correct if wrong, someone!

BTW, Smartreg NZ have those bolt on regulatorless bosch brush sets. $48nz
If its the alt I think it is. Or, I have a spare bosch regulated brushset you can butcher the internals to try and over-regulate it. (no charge) Problem is that will not be switchable unless you have another normal regulator in parallel with switches.
Curious to see how you resolve this?
By the time you have phaffed around reinventing the wheel you could have worked & bought a round one.
Yep, no fun tho'!

[lateral]

Post #19
https://www.cruisersforum.com/forums...-is-98527.html

[Wotname]

Originally Posted by Compass790

.....................
We have a switch in the field wire to cut the alternator out but we want some charging if possible.

Very Important Question Alert.

Does this field wire switch cut out the alternator when it is running or does it only cut out the alternator if switched open before the engine is started?

The answer will tell us if the field is internally excited or not.

All alternators (which use field current) require initial external excitement but most are then self exciting after start up by use internal field diodes. However some older alternators do not have any internal field diodes and therefore require an external field wire in order to maintain field excitation.

[Wotname]

As explained upthread, you don't have any direct control of the alternator output current. That means you only have indirect control.

Let's seperate the output loads into two sections -
1. battery charging
2. the rest i.e. lights, pumps, refrigeration etc.

The rest (#2) is easy, you simply turn them off and the current demand on the alternator is reduced.

Battery charging (#1) is more problematic. The easiest way to decrease charging amps is to reduce the charging voltage i.e. reduce the alternator output voltage.

Of course the regulator is trying to keep the output voltage constant.

So you have to fool regulator to lower the output voltage and that isn't easy (i.e. cheap) to do even with an external regulator let alone an internal regulator.

The only other cheap way to reduce charging current is to add series resistance into the battery charging circuit e.g. the bike spoke approach. While not a great method IMO, it will decrease the charging current and therefore the reduce alternator current.

If you pursue this idea, tread carefully!

[Compass790]

ble unless you have another normal regulator in parallel with switches.
Curious to see how you resolve this?
By the time you have phaffed around reinventing the wheel you could have worked & bought a round one.
Yep, no fun tho'![/QUOTE]

Yes true I could have worked & bought one much cheaper but my Baldrick philosophy seems to be to spend lots of hours to save $20.
I'm not in a hurry to resolve it as we use solar mostly but as you know there are some days the sun doesn't shine here.
I have some smoked VR's that I can cannibalize as brush sets, thanks for the offer though.

[Compass790]

Originally Posted by Wotname

As explained upthread, you don't have any direct control of the alternator output current. That means you only have indirect control.

Let's seperate the output loads into two sections -
1. battery charging
2. the rest i.e. lights, pumps, refrigeration etc.

The rest (#2) is easy, you simply turn them off and the current demand on the alternator is reduced.

Battery charging (#1) is more problematic. The easiest way to decrease charging amps is to reduce the charging voltage i.e. reduce the alternator output voltage.

Of course the regulator is trying to keep the output voltage constant.

So you have to fool regulator to lower the output voltage and that isn't easy (i.e. cheap) to do even with an external regulator let alone an internal regulator.

The only other cheap way to reduce charging current is to add series resistance into the battery charging circuit e.g. the bike spoke approach. While not a great method IMO, it will decrease the charging current and therefore the reduce alternator current.

If you pursue this idea, tread carefully!

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

[Compass790]

Originally Posted by Wotname

Very Important Question Alert.

Does this field wire switch cut out the alternator when it is running or does it only cut out the alternator if switched open before the engine is started?

The answer will tell us if the field is internally excited or not.

All alternators (which use field current) require initial external excitement but most are then self exciting after start up by use internal field diodes. However some older alternators do not have any internal field diodes and therefore require an external field wire in order to maintain field excitation.

The field wire switch turns the alt off when it is running.
The boat is fitted with 2 alternators to conform to Cat1 regs. I suspect the 55amp bosch has been modified by someone who knew what they were doing. The switch in the field wire is installed in the Yanmar instrument panel so easy to reach.