PWM controllers: Do they cause high voltage disconnect of inverters? Other voltage problems?

[Vigilant24]

This is a basic question, but I couldn't find an answer after searching a bit:

When I"ve got my inverter connected to the 12V batteries, will it "high voltage disconnect" if I'm also charging with a PWM controller being fed by 20V panels?

And, when charging with a PWM controller, can I use "nominal" 12V pumps, etc connected to my battery terminals?

Background: As I understand it, if a PWM controller is fed by, say, a panel producing 20V and 5 amps, the controller will
charge the battery at 20V and will modulate (rapidly cycle) the input charge on and off (from zero to 20V) to provide the correct average voltage and the right charge rate. If my inverter "sees" this 20V-Ov-20V-0V etc, it would seem logical that it could drop offline and generate a high voltage error. Likewise, if I've got a pump, fan, etc that is "expecting" to see continuous 12-14VDC, will it get that from the "12V" battery or will it get the "flickering" 20V from the PWM solar charge controller?

Thanks.
Mark

 

[zanydroid]

You are forgetting that the solar panel and battery will reach an equilibrium voltage. And it cannot be that much higher than the battery voltage, otherwise there would be way too much current going into the battery.

So it’s more like swing between (battery voltage + V, battery voltage), where V is determined by the solar panel size and analog characteristics of the circuit.

 

[HarryN]

This is a basic question, but I couldn't find an answer after searching a bit:

When I"ve got my inverter connected to the 12V batteries, will it "high voltage disconnect" if I'm also charging with a PWM controller being fed by 20V panels?

And, when charging with a PWM controller, can I use "nominal" 12V pumps, etc connected to my battery terminals?

Background: As I understand it, if a PWM controller is fed by, say, a panel producing 20V and 5 amps, the controller will
charge the battery at 20V and will modulate (rapidly cycle) the input charge on and off (from zero to 20V) to provide the correct average voltage and the right charge rate. If my inverter "sees" this 20V-Ov-20V-0V etc, it would seem logical that it could drop offline and generate a high voltage error. Likewise, if I've got a pump, fan, etc that is "expecting" to see continuous 12-14VDC, will it get that from the "12V" battery or will it get the "flickering" 20V from the PWM solar charge controller?

Thanks.
Mark

Just as an example, I routinely use a bogart PWM solar charge controller in 24 volt systems.

The power system in my ford explorer is done this way. Nominal 24 volt panel (so ~ 36 ish volt Vmp ) feeding a small bus bar and 2 each 100 amp -hr batteries wired in series. Inverter, 24 volt DC loads, DC- DC converter for 12 volt loads, etc. LED strip lights, etc.

I have had it hooked up to solar arrays from 200 - 600 watts and it is a non issue.

Even with fairly decent DMM I can't see the voltage surging but it obviously isn't an oscilloscope analysis.

 

[HarryN]

Part of the reason that there isn't much voltage excursion is the battery.

I use either Lifeline or Battle born batteries and they can charge / discharge at fairly high rates compared to most PWM charge controllers.

There just is not much voltage ripple that passes through a battery pack unless it is fairly extreme situation.

Even 600 watts into a 24 volt battle born is only ~ 50% of it's designed charge rate and the ripple from a charger will be much less.

Similar on a Lifeline AGM pack - fairly large ability to charge / discharge - really higher than many LiFe of similar size under surge loads.

I didn't try it on very small battery packs.

 

[Vigilant24]

Part of the reason that there isn't much voltage excursion is the battery.


Similar on a Lifeline AGM pack - fairly large ability to charge / discharge - really higher than many LiFe of similar size under surge loads.

I didn't try it on very small battery packs.

The project I'm working on has two 110AH 12V FLA batteries in parallel. This is a strictly a "drag it out of the closet in an emergency" system, and I'm planning on four 100W panels (20V VMP , 5A IMP each). Since efficiency isn't super important in this role, but flexibility, cost, and reliability is, I'm thinking about just going with one cheapie "30A" PWM controller for each panel (about $30 total additional, I already own 2) rather than than spend $150 for a single 30-40A MPPT controller. If anthing happens to my single MPPT controller, I'd be effectively out of business entirely. With a bunch of PWM controllers I could keep running in a degraded mode (paralleling panels into remaining controllers, even re-wiring the battery pack to 24V for charging only etc) even with 3 dead controllers.
But, I was concerned about this voltage ripple issue with PWM controllers because I'd really like to be able to run my inverter or "12V" pumps, etc without a problem.

Thanks again to all, additional comments are sought/welcome.

Mark

 

[SamDeleted]

When it comes to 12v equipment (inverters, pumps, ect.) some are voltage sensitive, but almost all aren't , most will run from a range of voltages 10v to 15.5v

Your PWM charge controller takes the 20v your panels make , and cuts it down to the appropriate voltage for charging your battery .... Eg. 14.5v-15.5v~ (depending on battery chemistry)

 

[SamDeleted]

But, I was concerned about this voltage ripple issue with PWM controllers because I'd really like to be able to run my inverter or "12V" pumps, etc without a problem.

Don't worry about the PWM , it's actually better for your lead acid batteries , my big 48v system is on a PWM charge controller

It's not as efficient, but more reliable

 

[HarryN]

The project I'm working on has two 110AH 12V FLA batteries in parallel. This is a strictly a "drag it out of the closet in an emergency" system, and I'm planning on four 100W panels (20V VMP , 5A IMP each). Since efficiency isn't super important in this role, but flexibility, cost, and reliability is, I'm thinking about just going with one cheapie "30A" PWM controller for each panel (about $30 total additional, I already own 2) rather than than spend $150 for a single 30-40A MPPT controller. If anthing happens to my single MPPT controller, I'd be effectively out of business entirely. With a bunch of PWM controllers I could keep running in a degraded mode (paralleling panels into remaining controllers, even re-wiring the battery pack to 24V for charging only etc) even with 3 dead controllers.
But, I was concerned about this voltage ripple issue with PWM controllers because I'd really like to be able to run my inverter or "12V" pumps, etc without a problem.

Thanks again to all, additional comments are sought/welcome.

Mark

FLAs don't necessarily store all that well and retain charge.

Perhaps consider to find a regular use for them to power something?

Not sure about buying ultra cheap pwm controllers as a way to improve reliability through numbers. I have people come in with vans that have renogy pwm controllers that have failed - swap them out for a bogart and off they go for years.

There is a very simple way to set up FLA vs AGM and 12 vs 24 volt on the bogart - just move a couple of setting pins and you are done.

They are about $100 I think.

If you can, try to find a panel with a Vmp that is slightly lower and a current that is a bit higher. Those will work better with a PWM.

 

[HarryN]

Don't worry about the PWM , it's actually better for your lead acid batteries , my big 48v system is on a PWM charge controller

It's not as efficient, but more reliable

The bogarts that I use only go up to 24 volts. Have not found any good 48 volt yet. Which 48 volt PWM do you use?

Thanks.

 

[SamDeleted]

The bogarts that I use only go up to 24 volts. Have not found any good 48 volt yet. Which 48 volt PWM do you use?

Thanks.

Morningstar TS-60 ... They don't come cheap lol !

 

[sunsurfer]

Don't worry about the PWM , it's actually better for your lead acid batteries , my big 48v system is on a PWM charge controller

It's not as efficient, but more reliable

Some MPPT charge controllers may use PWM on the battery side vs a linear regulator to maintain the desired charging/float voltage.

 

[zanydroid]

What MPPT charge controllers use a linear regulator? That would be rather inefficient, might defeat the advantage of tracking by burning the extra energy harvested in the linear regulator and require a big heat sink on the charge controller.

An MPPT will typically use an 80-95% efficient DC-DC converter to adapt down to the target charging voltage, and there is a PWM sort of control loop involved in this but it is intended to harvest as much power as possible. My understanding is that a straight PWM is primarily concerned with providing a safe, regulated charge current.

 

[sunsurfer]

What MPPT charge controllers use a linear regulator? That would be rather inefficient, might defeat the advantage of tracking by burning the extra energy harvested in the linear regulator and require a big heat sink on the charge controller.

An MPPT will typically use an 80-95% efficient DC-DC converter to adapt down to the target charging voltage, and there is a PWM sort of control loop involved in this but it is intended to harvest as much power as possible. My understanding is that a straight PWM is primarily concerned with providing a safe, regulated charge current.

I don't know what else would be used on the charging side vs PWM. Way out of my area of expertise. I have just read "some" MPPTs use PWM regulation for the charger side. Someone with more knowledge could clarify what else would work in place.

Someone in this tread mentioned the advantage of using a PWM controller vs MPPT for lead acid(not sure why) and I just wanted to point out the charging end on at least some(all?) MPPT SCCs is in fact PWM on the output.

Thanks for clarifying the linear reg issue. I read up on it and they are power hungry.

 

[zanydroid]

Here is a very well written up DIY MPPT module that covers a lot of this. It talks about the places where PWM is used in an MPPT.

https://www.instructables.com/DIY-1kW-MPPT-Solar-Charge-Controller/