Connect DC charger to SCC?

[PfloydBham]

This may seem like a dumb question, but I don't have much experience with solar power. So, please just overlook my ignorance.
I am curious if I can connect an ebike charger to my Epever BN which is set for a Tesla S battery in a small travel trailer. the ebike charger is 29.4 volts at 3 amps. My panels are set up in series at about 36v and 9 amps. Not that I am going to "rig" something up, but I was curious as to if it would work and what problems could occur. Any comments would be helpful, Thanks.
Pink

 

[Bob142]

Not a dumb question at all.

Edit: Just a dumb answer...
Edit Feb 14: Maybe not a dumb answer for MPPT (I tested it. See below.)

DC chargers are connected to SCC inputs all the time in portable power stations from Jackery, Goal Zero, Bluetti, etc. Edit: But clearly maybe there's some other input circuitry to manage things so as to play nice with the battery charging if PWM.

As long as your ebike charger voltage is below the max PV open circuit voltage specified by your SCC (no problem with that in your case) and is higher enough than your battery bank voltage (24V-ish for Tesla S battery?) to start the SCC charging it should work fine.

 

[PfloydBham]

Thanks!!! That's a major breakthrough for me. I don't want to speak too soon, but I may be starting to put some of the pieces together. Would that concept work with a PWM SCC, also? Does it matter if the SCC is PWM or MPPT as long as I have the settings correct for the chemistry? I have a HQST PWM that claims to have a user defined parameter. again, I do not intend to build this setup, but it is becoming very educational for me understanding how the charge potential seems to work and what the limits are. I am reluctant to take risk when I do not fully understand what I am doing. Again, thanks.
Pink

 

[Bob142]

Would that concept work with a PWM SCC, also?

Edit: Definitely no without additional circuitry between DC charger and PWM (see failed experiment below).
Edit Feb 14: Maybe yes (see latest experiment).

Yes. I've got two Jackerys and two GZs that have built-in PWM SCCs and you just plug the wall charger into the same input jack as the solar panels.

If you give me another day or two I'll put together a rig with a laptop charger and a small PWM SCC charging a battery and post it here. I'm not expecting any smoke (famous last words? ) Edit: No smoke, just an over voltage error and cutoff of SCC.

 

[PfloydBham]

Awesome! Can't wait to see it.
I've got a bunch of "Pieces -parts" I want to rig into some small projects. Mostly just to get a practical take on how these "doo-dads" work together. Ultimately, I want to augment some day to day applications in home and likely go to some type of "grid associated" setup, but I would like to understand what I am doing, --- at least to some degree.

 

[Bob142]

Been doing some reading on the train ride home. There could be smoke. Now I can’t wait to mess with it!

 

[Bob142]

Laptop charger into PWM = FAIL. Over voltage error. Clearly I need to pull apart one of my Goal Zeros and see what else happens on the input circuit as I made a bad assumption it was just a PWM charge controller. I forgot that they basically pull the panel voltage down to battery voltage and you can't do that to a power brick. I went back and edited my bad answers above. I'll try an MPPT tomorrow/Sat to see if I can smoke that.

 

[Tremors834]

Interesting. What were the specs/ratings of the laptop charger and the PWM SCC?

 

[Bob142]

20V 3.25A charger (old Lenovo that I was willing to strip off the barrel plug). Renogy 10A PWM with 50V max input voltage. 12V 26Ah AGM battery.

It brought the battery voltage up over 16V quickly, so the PWM disconnected the battery with an over voltage error.

Looking at my GZ charger it’s 16V 5A. I believe that’s still too high a voltage to plow directly into a 12V battery so something else likely happens at the GZ input. It doesn’t seem like it’s just a PWM SCC circuit.

 

[Tremors834]

Hmmm. That 20v seems high. Especially for a PWM as you stated. I don't speak from knowledge as I am just starting to understand solar, but if I am thinking correctly, That 20v is higher than say the 16v of a 100w panel that I just checked the specs on. So I guess it's safe to say it's the 20v that's the issue
I also read that MPPT SCCs can accept the higher input voltage (as if you we were connecting your panels in series), which you have already alluded to.
Thanks. This is interesting.

 

[Bob142]

I'm trying to figure it out as well. With a solar panel as input to the PWM, the voltage of the panel is supposed to be pulled down to the battery voltage. I've observed exactly that with a 50W panel connected to the PWM and the battery used in this experiment. The panel and battery voltages matched until the SCC went into float mode. However, a few weeks ago I tried the same panel and PWM combo on a much smaller 9Ah battery. It seemed to work while it was cloudy, but as soon as it got sunny it started throwing over voltage disconnect errors and the panel was at 18V rather than at battery voltage. That should have been a clue that this experiment wouldn't work. I've got to study things more and figure out what the heck the GZs do.

 

[Bob142]

Laptop charger into MPPT = SUCCESS.

Pic sequence:
1: Before plugging in laptop charger
2: Laptop charger plugged in, MPPT charging battery
3: Renogy Bluetooth app view during charging
4: Laptop charger specs



Next up: discharge an old GZ Extreme 350 (lead acid) and observe battery voltage during wall and solar charging. 100 years ago when I bought it, it was touted as using PWM charging. I've equated that to a standard PWM SCC, but I was dead wrong. Can't wait to figure out what it actually does (maybe more of a trickle charger and that's why it's so slow?)

 

[Bob142]

Hold on a minute! New PWM test based on something I observed with my crappy little Renogy PWM and a solar panel earlier today. I noticed that if I connect the panel to the PWM and the battery is depleted a bit, the Renogy charges it fine. If I start with an almost full battery, the Renogy freaks out and brings the battery up to 16V quickly and goes into over voltage disconnect error just like my laptop charger test from last night.

So, round 2 of Laptop Charger vs. PWM: Don't try this at home.
I started with the same 12V 26Ah battery but ran it down to about 12.5V. Then I connected up the test rig as I did last night.
It's WORKING...

Pic sequence:
1: The rig just after plugging in, waiting to burn down my kitchen
2: Renogy Bluetooth app, shortly after charging started
3: Close up of PWM SCC screen, "panel" voltage after a short while
4: PWM SCC screen, "panel" current
5: PWM screen, battery voltage
6: App view after short while of charging






The laptop brick is getting a little warm, but admittedly I never check it when it's charging the laptop so I don't know if it's normal or not.

Edit: I just aborted the mission because the laptop brick started buzzing. Pretty sure this NOT how you want to charge your battery. Buy a proper wall charger.

 

[Tremors834]

Wow. Thanks for these tests. Quite interesting. Maybe the laptop charger issue is due to it being a switching power supply? I don't know, definitely getting into areas that I have no business speculating on. LOL.

I've placed an order for a number of items. 1 being a lifepo4 charger. When I receive it I'll try feeding it directly into my Renogy MPPT to see what the results are.

If I had a varriable power supply I would try that as well. I guess that's my next order.