Solar controller as an el- cheapo smart regulator?

[Compass790]

Originally Posted by RaymondR

It might actually work.

What all alternator regulators do is vary the rotor current to control the field output current and voltage. Pre electronic regulators this was done by opening and closing mechanical switches with a solenoid so one might say it was switch mode control. However due to a degree of hysterisis the rectifying diodes experienced pulsating current levels rather than a series of spikes.

If you could rig the solar regulator to independently sense the battery voltage and have that control the rotor current it might work.

Thanks, you are the first to say it's a possibility. Trouble is the battery voltage will be the same as the voltage supply to the field wire ASFAIK but I know very little. I ASSUME the solar controller must sense the battery voltage thru the battery terminals on the controller but I need to make the solar controller the current control on the field wire so the field wire would have to go in the PV panels terminals & out the battery terminals.
This maybe total nonsense as i say I don't have much electrical knowledge but I wont take it to heart if you say it's not right.

[Reefmagnet]

When I rigged an MPPT solar regulator to a DC power supply for testing, recently, I forgot about it being connected and it almost fried the DC supply after a while because the regulator pulls as much power from the source as the source can supply. This makes sense when connected to a solar panel, but it will result in the alternator output being maxed out for extended periods which might not be conducive to long term reliability. Just a heads up!

[Compass790]

Originally Posted by Reefmagnet

When I rigged an MPPT solar regulator to a DC power supply for testing, recently, I forgot about it being connected and it almost fried the DC supply after a while because the regulator pulls as much power from the source as the source can supply. This makes sense when connected to a solar panel, but it will result in the alternator output being maxed out for extended periods which might not be conducive to long term reliability. Just a heads up!

Thanks for the heads up. But doesn't an ordinary alternator voltage regulator pull as much power from the alternator as it can produce until the volts rise to the setpoint?
Are you saying the solar controller will increase the field current beyond the normal 4 amps or so?

[RaymondR]

Originally Posted by Compass790

Thanks, you are the first to say it's a possibility. Trouble is the battery voltage will be the same as the voltage supply to the field wire ASFAIK but I know very little. I ASSUME the solar controller must sense the battery voltage thru the battery terminals on the controller but I need to make the solar controller the current control on the field wire so the field wire would have to go in the PV panels terminals & out the battery terminals.
This maybe total nonsense as i say I don't have much electrical knowledge but I wont take it to heart if you say it's not right.

The solar controllers usually vary the current from the controller to the battery and do not care what the solar panel voltage is other than it be lower than the controllers voltage limit and sufficiently high enough to overcome the battery back voltage which will depend on the batteries state of charge and the amount of current being forced back through it.

Some controllers have the capability to sense the battery voltage through a connection directly to the battery terminal.

There are two ways that the excitation current is passed through the rotor of an alternator; one where a current source is connected to the regulator and the regulator then controls the excitation current into and through the rotor coil which is earthed, and the second, where the rotor coil is internally connected to a current source within the alternator and the regulator controls the current coming out of the rotor coil and connects it to earth.

To do what you want to do you will either have to connect the panel terminal of the regulator to the positive supply and the battery terminal on the regulator to the rotor connection or the panel terminal to the rotors earth connection.

Years ago I used to use a motor speed controller connected so to bypass the regulator on an alternator and manually control the charging. If they had had cheap solar controllers available at that time I may have tried what you have suggested, it's a good idea.

I have used a transformer feeding paralleled diode bridges to supply unregulated DC to the panel terminal of an expensive solar controller to charge batteries because a high ampage battery charger was to expensive.

[Reefmagnet]

Originally Posted by Compass790

Thanks for the heads up. But doesn't an ordinary alternator voltage regulator pull as much power from the alternator as it can produce until the volts rise to the setpoint?
Are you saying the solar controller will increase the field current beyond the normal 4 amps or so?

No. I'm simply suggesting that the way a solar controller works could place strain on a standard alternator as my observation when using a constant voltage power supply was that the mppt controller placed it into an overload condition because the only way the mppt controller can react to the loading of the source is the voltage drop of the source under load. I suspect this could cause the load current draw to "hunt" on anything trying to maintain a constant voltage under load (which is exactly the purpose of a voltage regulator). Solar panels work because they do not output a constant voltage.

[newhaul]

I have politely suggested not doing it . Now the question .
How often do you want to replace your alternator? We have been having this type of discussion concerning alternator and Lfp batteries . Here is what is a likely scenario. Your battery reaches the set point of the solar controller . Now your alternator output has no place to go . Not a ramping down such as happens when batteries get close to fully charged but a sudden stopping . Your alternator internal diodes will almost instantly cook.
Dead alternator.

[Compass790]

Originally Posted by RaymondR

The solar controllers usually vary the current from the controller to the battery and do not care what the solar panel voltage is other than it be lower than the controllers voltage limit and sufficiently high enough to overcome the battery back voltage which will depend on the batteries state of charge and the amount of current being forced back through it.

Some controllers have the capability to sense the battery voltage through a connection directly to the battery terminal.

There are two ways that the excitation current is passed through the rotor of an alternator; one where a current source is connected to the regulator and the regulator then controls the excitation current into and through the rotor coil which is earthed, and the second, where the rotor coil is internally connected to a current source within the alternator and the regulator controls the current coming out of the rotor coil and connects it to earth.

To do what you want to do you will either have to connect the panel terminal of the regulator to the positive supply and the battery terminal on the regulator to the rotor connection or the panel terminal to the rotors earth connection.

Years ago I used to use a motor speed controller connected so to bypass the regulator on an alternator and manually control the charging. If they had had cheap solar controllers available at that time I may have tried what you have suggested, it's a good idea.

I have used a transformer feeding paralleled diode bridges to supply unregulated DC to the panel terminal of an expensive solar controller to charge batteries because a high ampage battery charger was to expensive.

Thank you very much for taking the time to reply in such a manner that I can understand. Particularly liked the last part about yr use of solar controller as high amp charger My kinda bloke
Our alternator has the +field wire going directly to a rotor brush & its voltage regulator interrupts the path to earth. I have to wait for a spare solar controller to come before I try the idea out, may not happen for a few mths. Will use existing 20amp PWM solar controller that I got for 99c on Ebay. It has been going since 2015 so I got my moneys worth.lol
Dont want to mess with system in summer.
cheers

[Compass790]

Originally Posted by Reefmagnet

No. I'm simply suggesting that the way a solar controller works could place strain on a standard alternator as my observation when using a constant voltage power supply was that the mppt controller placed it into an overload condition because the only way the mppt controller can react to the loading of the source is the voltage drop of the source under load. I suspect this could cause the load current draw to "hunt" on anything trying to maintain a constant voltage under load (which is exactly the purpose of a voltage regulator). Solar panels work because they do not output a constant voltage.

Ok thanks. I take yr point. I will monitor alternator temp with my DMM thermocouple & see what happens. I will be using a PWM controller tho, wouldnt risk MPPT even if I had one. I'm assured that some alternator voltage regulators are PWM anyway

[Compass790]

Originally Posted by newhaul

I have politely suggested not doing it . Now the question .
How often do you want to replace your alternator? We have been having this type of discussion concerning alternator and Lfp batteries . Here is what is a likely scenario. Your battery reaches the set point of the solar controller . Now your alternator output has no place to go . Not a ramping down such as happens when batteries get close to fully charged but a sudden stopping . Your alternator internal diodes will almost instantly cook.
Dead alternator.

I have politely requested a reason for not doing it in my OP. I simply need a logical explanation of why not to do it. It's not enough for me to have someone say "not recommended" or "can't do it" I wish to learn something about the problem. In your first post you gave no reason. Thanks for putting a reason in this time
Other people disagree with your reason & I quote :"Just as a BTW, there is no problem switching field current on and off, you can do it all you want. It's only on the output side that you can create problems.Indeed, some alternator regulators are just PWM controllers. No problem putting one on the field side of the alternator. Now, as to how it will work and whether it will do what you want? Not sure, as I'm not sure how it would sense the battery voltage."
This was sent to me in a PM
N.B. the solar controller will be in the field wire tho I did start the thread saying I wanted to put it on the output side but I was given a perfectly logical reason not to do that so I abandoned the idea

[RaymondR]

Originally Posted by Compass790

Thank you very much for taking the time to reply in such a manner that I can understand. Particularly liked the last part about yr use of solar controller as high amp charger My kinda bloke
Our alternator has the +field wire going directly to a rotor brush & its voltage regulator interrupts the path to earth. I have to wait for a spare solar controller to come before I try the idea out, may not happen for a few mths. Will use existing 20amp PWM solar controller that I got for 99c on Ebay. It has been going since 2015 so I got my moneys worth.lol
Dont want to mess with system in summer.
cheers

No problem.

I think we are going to see a lot more of this sort of experimentation in the future when lithium batteries go down in cost and we want to exploit their fast charging capabilities.

[john61ct]

Some solar controllers, especially PWM and those designed to also handle wind power, can tolerate non-panel inputs.

Some cannot, basically need to try and see, carefully monitoring.

Quality LFP cells will likely not be getting cheaper, and I would only to use want quality, setpoint adjustable gear. Saving a couple hundred bucks should not be a factor compared to safety and reliability.

[Compass790]

Originally Posted by john61ct

Some solar controllers, especially PWM and those designed to also handle wind power, can tolerate non-panel inputs.

Some cannot, basically need to try and see, carefully monitoring.

Quality LFP cells will likely not be getting cheaper, and I would only to use want quality, setpoint adjustable gear. Saving a couple hundred bucks should not be a factor compared to safety and reliability.

Thanks for your advice,
Notice you comment on electrical stuff quite a bit ( I spend far too much time on CF avoiding my chores! ) & you seem to make sense, tho I'm not qualified to judge.

I'm not risking much then ( hopefully) tryn out my 99c PWM controller on the field wire as I will monitor alt temps for a trial. At least now I wont blow up rectifier bridge since I was warned about putting it on output side in first reply to thread
. Newhaul put me on to discussion about alternator/charging for lithium so learnt a lot off that thread.

Wont be going Li. anytime soon way as hope to get at least 10 more years out of our deep cycle FLA.

It's been good consulting the CF hive :-)