Hooking up a power supply to MPPT solar charger’s PV input

[moonlight23]

I’m building a portable DIY power station with 8S LiFePO4 batteries (24v), with a Victron 100V/15A MPPT solar charge controller inside to charge the batteries.

However I also want the option to charge this battery pack from the AC wall outlet. Can I wire both the solar panels and THIS 120v AC to 48v DC rectifier power supply into the PV input of the Victron? This would mean that if solar panels are not connected, the MPPT would still have a supply of 48v DC fed into it to charge the batteries from the wall.

That power supply linked is only rated for 4A (I’m ok with the slower charging speeds), however I’m a little concerned it’s not actually current-limited, so if the MPPT wants to pulls more than 4A then it could fry both the power supply and MPPT.

 

[Supervstech]

No, that supply is current limited to 4 a max, I would get one of the 20a supplies

 

[JamesRich]

I've done it with a 24v power supply to 12 volt battery. Worked good for a few days till the regulator went on the power supply. The regulator had recently been replaced though so I think it had a previous problem, not damaged from the mppt pulling too much.
James

 

[moonlight23]

No, that supply is current limited to 4 a max, I would get one of the 20a supplies

You’re correct. After doing some more research, I realized this will not work because the solar charger will pull 15A max and will overload that 48v 4A power supply. I don't think there's any current-limiting circuitry in there, so if more than 4A draw is sustained, it will eventually go pop.

The alternative I found is this 36v 16A Meanwell LOP-36 power supply. Any issues if I use this PSU instead?

Do I need to use any diodes so solar power does not back-feed into the PSU, or the PSU doesn’t back-feed into the PV panels?

 

[B-ManFX4]

I am considering doing this but I am hesitant because I read this on the spec sheet of my 75/10:

Max. PV short circuit current 2): 13 A

When you go to the bottom of the page to read Note 2), it says:

2) A PV array with a higher short circuit current may damage the controller.

Is that insinuating that if more than 13 amps is available from the source that the controller may be damaged?

 

[mikefitz]

Any issues if I use this PSU instead?

Current limit is poor on these units, will fold back or fail.

Is that insinuating that if more than 13 amps is available from the source that the controller may be damaged

This is only under reversed polarity of the solar input, not under correct connection conditions.

Suggest you install a 24v Victron Blue Smart IP 65 charger direct on the battery. A better engineering solution.

 

[B-ManFX4]

Current limit is poor on these units, will fold back or fail.

This is only under reversed polarity of the solar input, not under correct connection conditions.

Suggest you install a 24v Victron Blue Smart IP 65 charger direct on the battery. A better engineering solution.

Where do you see this reverse polarity information ?

 

[mikefitz]

Where do you see this reverse polarity information

Manual, page 62 and 63.

 

[upnorthandpersonal]

Why not use a telecom rectifier, like the ones we discussed here:

DIY 'Chargenectifier'

Based of the informative info recently posted by @ChrisFullPower in another thread I'm intrigued in DIY'ing a charger from used rectifiers. A quick search on eBay for '48v rectifier' has made me realize it's definitely doable at costs much lower than off the shelf options... I'll start with a...

diysolarforum.com

I use a 3kW R48-3000e3. Around 100 Euro (used) including shipping from Aliexpress.

https://www.aliexpress.com/item/1005003755306962.html

Granted, I use this to charge a 48V pack directly, but you could put this on the charge controller.

 

[Warpspeed]

The system I am running right now has a solar controller connected to my lithium battery in the usual way.
Because my battery is limited in size, I sometimes need to supplement solar with dc power from the grid when its very cloudy for several days in a row.

After trying quite a few different ways to do this, by far the best, is to run an efficient switched mode dc power supply (continuously from the grid) during bad weather, connected to the battery through a diode.
The power supply is set to the MINIMUM acceptable battery voltage, plus one diode drop. That prevents the battery voltage from falling any lower than the set minimum.

The switching power supply draws almost negligible power from the grid most of the time, but it should be made sufficiently large to handle the largest expected continuous inverter loads. The battery is still there with some life left in it, and the battery can still handle any short term surge loads that may be beyond the current limit in the dc power supply.

The way this might work for you, assume the lowest safe voltage might be 3.1v per cell. Eight series cells = 24.8v minimum.
Set the voltage at the dc switching power supply output to 24.8v + 0.6v = 25.4v

You can now just let the system run, and it will take care of itself.
Grid power is only used when the battery gets very low, and no extra grid power is used to fully recharge the battery.
The sun does that !
During summer I leave the power supply switched off, its just not necessary.
During winter its just brilliant, everything runs fine, drawing absolutely minimal grid power only at the worst times to do it.

 

[B-ManFX4]

Manual, page 62 and 63.
View attachment 214629View attachment 214630

Not my manual. I posted the entirety of the warning above and it says nothing about reverse polarity.