Using a MPPT as a battery charger?

[GSXR1000]

can I use a 75/15 as a 24v to 12v battery charger? both batteries are Lifepo4.

 

[jall]

Hi.
It is suposed that it is the intended function of the 75/15 as long as you use the "batt" terminals for the connection.
Another question is if you use more than one single bat and each one is of diferent capacities, or even more important if each one are of different technologies, since the unit can ONLY monitor and regulate ONE of them. In case you have for instance an RV with LIPO on the rear and lead-acid for the engine, you can use the output "Load" for the lead-acid one (although I recomend the use of an aditional regulator in series for it)

Jose

 

[sunshine_eggo]

I would expect so. Will has demonstrated many times that using a 30V/10A PS as input to a MPPT works fine.

 

[GSXR1000]

Hi.
It is suposed that it is the intended function of the 75/15 as long as you use the "batt" terminals for the connection.
Another question is if you use more than one single bat and each one is of diferent capacities, or even more important if each one are of different technologies, since the unit can ONLY monitor and regulate ONE of them. In case you have for instance an RV with LIPO on the rear and lead-acid for the engine, you can use the output "Load" for the lead-acid one (although I recomend the use of an aditional regulator in series for it)

Jose

no.. 24v battery would goto pv input and batt to 12v

 

[DThames]

I would expect so. Will has demonstrated many times that using a 30V/10A PS as input to a MPPT works fine.

The power supply was current limited. If the battery is large enough the Victron should limit at its rated current.

You can use a buck converter as a charger. The one linked has low voltage cutoff so it will not drain your source battery too much. I have been using a boost converter of similar design to charge 36v off of 24v. You can't run it at the full watts under most conditions. I can run about 400 watts output and the fan is off and on as needed, so it is not being pushed much at 400w. Be careful to connect the source battery first. Some can be weird if source not connected and output has juice. It is not for someone that don't understand. You have to carefully adjust it for your specific needs. Adjust output voltage, output current limit, and low voltage cutoff.

 

[sunshine_eggo]

I would expect so. Will has demonstrated many times that using a 30V/10A PS as input to a MPPT works fine.

I would put a fuse between the 24V and the PV input that corresponds to the max PV input current listed for the mppt

 

[jall]

no.. 24v battery would goto pv input and batt to 12v

Oops... sorry I didn´t read it all. I thought you wanted one 24 PV panel with two batteries. Sorry for the confussion.
It should work as you said, but I am not sure what will do the MPPT with an almost plain voltage curve. I supose you can switch the MPPT off in order to no interfere.

 

[mikefitz]

No, Victron do not recomend using a battery as an input source to the MPPT, it will cause damage, use DC to DC 24 to 12 charger. Victron Orion 24 12 20,

Orion-Tr Smart DC-DC Charger Isolated - Victron Energy

The Orion-Tr Smart DC-DC charger is a professional DC to DC adaptive 3-stage charger with built-in Bluetooth. For use in dual battery systems in...

www.victronenergy.com

It's possible to use a current limited power supply but not a battery.

Mike

 

[GSXR1000]

No, Victron do not recomend using a battery as an input source to the MPPT, it will cause damage, use DC to DC 24 to 12 charger. Victron Orion 24 12 20,

Orion-Tr Smart DC-DC Charger Isolated - Victron Energy

The Orion-Tr Smart DC-DC charger is a professional DC to DC adaptive 3-stage charger with built-in Bluetooth. For use in dual battery systems in...

www.victronenergy.com

It's possible to use a current limited power supply but not a battery.

Mike

of course victron wouldn't recommend it... they wouldn't recommend a DIY battery either.....
you can set the current in the mppt so it has current regulation and at a much higher voltage so don't see how a current limit on supply is required when that happens internal limiter...

I do agree that it isn't using as intended.. but your reason is cuz oem said so

 

[BradCagle]

I would not do that.

I see guys hooking up power supplies, and even batteries to MPPT ports. It may only be working as a stroke of luck. Not good practice.

I experimented with this, and some MPPTs will load a PSU down so hard the PSU will go into fault, and shut off.

The MPPT algorithm goes wild pulling the load down further, and further because it appears to the MPPT as it's milking more, and more power.
Maybe limiting the charge current in the MPPT would help, but I still don't think it's good practice.

 

[DThames]

I would not do that.

I see guys hooking up power supplies, and even batteries to MPPT ports. It may only be working as a stroke of luck. Not good practice.

I experimented with this, and some MPPTs will load a PSU down so hard the PSU will go into fault, and shut off.

The MPPT algorithm goes wild pulling the load down further, and further because it appears to the MPPT as it's milking more, and more power.
Maybe limiting the charge current in the MPPT would help, but I still don't think it's good practice.

I agree this is not a practice that anyone should do, but in your experiments, was the power supply a current limited supply that could tolerate a short circuit output? I would guess/expect that as the MPPT pulled it down, our of regulation that the MPPT could do the math and see the power (volts times amps) going down and let up a bit. Did that not happen?

 

[BradCagle]

I agree this is not a practice that anyone should do, but in your experiments, was the power supply a current limited supply that could tolerate a short circuit output? I would guess/expect that as the MPPT pulled it down, our of regulation that the MPPT could do the math and see the power (volts times amps) going down and let up a bit. Did that not happen?

A little back story. The company I work for has a IOT system that runs on solar. Basically a 20a EPEver MPPT, 200w panel, and 100ah LiFePO4
I wanted the guys in the shop to be able to maintain/charge these units before they go out to a new site. I experimented hooking up POE power supplies that have 54vdc out to the MPPT. I went through several, some were rated 2.5a, and some 5a.

They all had the same problem, it would initially work but the MPPT would pull it down, then PSU shuts off, then comes back in a cycle. Also managed to totally kill a few of the PSUs

 

[sunshine_eggo]

I would not do that.

I see guys hooking up power supplies, and even batteries to MPPT ports. It may only be working as a stroke of luck. Not good practice.

I experimented with this, and some MPPTs will load a PSU down so hard the PSU will go into fault, and shut off.

The MPPT algorithm goes wild pulling the load down further, and further because it appears to the MPPT as it's milking more, and more power.
Maybe limiting the charge current in the MPPT would help, but I still don't think it's good practice.

I'm going to trust the President of MidNite Solar over you:

Testing MPP Charge controller function with bench power supply?

Anyone know if you can use a 5A-60V DC power supply to test functioning of a MPP charge controller. I have a all in one inverter with charge controller that I am testing in my shop before shipping to where it will be installed in MX. Everything is working great but don't have PV panels here and...

diysolarforum.com

"We do it all the time."

 

[sunshine_eggo]

A little back story. The company I work for has a IOT system that runs on solar. Basically a 20a EPEver MPPT, 200w panel, and 100ah LiFePO4
I wanted the guys in the shop to be able to maintain/charge these units before they go out to a new site. I experimented hooking up POE power supplies that have 54vdc out to the MPPT. I went through several, some were rated 2.5a, and some 5a.

They all had the same problem, it would initially work but the MPPT would pull it down, then PSU shuts off, then comes back in a cycle. Also managed to totally kill a few of the PSUs

That's likely what happens when you use undersized power supplies.

20A controller fed by power supply capable of 9-10A output @ battery voltage = poor design choice.

Even the 5A power supply can't supply enough power @ 20A/14.4V.

It should be a given that the power supply can provide more power than the output of the MPPT.

 

[BradCagle]

I'm going to trust the President of MidNite Solar over you:

Testing MPP Charge controller function with bench power supply?

Anyone know if you can use a 5A-60V DC power supply to test functioning of a MPP charge controller. I have a all in one inverter with charge controller that I am testing in my shop before shipping to where it will be installed in MX. Everything is working great but don't have PV panels here and...

diysolarforum.com

"We do it all the time."

Good for you!

 

[sunshine_eggo]

Good for you!

Thanks!

Maybe consider that you're making conclusions and offering advice from your own personal experience based on bad designs choices.

 

[740GLE]

Victron has short circuit current limits for the input for their SCC for a reason if your dc input is inside those parameters it’ll be fine.

 

[BradCagle]

That's likely what happens when you use undersized power supplies.

20A controller fed by power supply capable of 9-10A output @ battery voltage = poor design choice.

Even the 5A power supply can't supply enough power @ 20A/14.4V.

It should be a given that the power supply can provide more power than the output of the MPPT.

Well the battery is setup for 24v on these. But I got ya, 5A @ 54v is not alot, but It' comparable to that 5A-60vdc mentioned in the link.

I actually have one of these IOT setups on my desk, I might play with current limiting in the EPever to see if it'll work.

 

[mikefitz]

The OP wants to connect a 24 volt lithium battery to the input of a 15 amp MPPT controller, not a power supply.

 

[sunshine_eggo]

The OP wants to connect a 24 volt lithium battery to the input of a 15 amp MPPT controller, not a power supply.

With suitable OCP, I don't see a problem.