Connected two 48V chargers in parallel, internal spark

[Jalle19]

I would like to connect three Sunpower SP-750-48 (rebranded Mean Well) chargers in parallel (ultimately the idea is to build a 2S3P three-phase charger for an EV, but that's beside the point right now).

When experimenting, I connected two chargers in parallel on the DC side, then connected one of the chargers to AC. Both chargers turned on, but after around two seconds, a big spark happened inside the charger that wasn't connected to AC. After disconnecting everything and inspecting the sparked charger, no visual damage was found, and in fact the charger still worked normally. I didn't dare to try again.

What could be the reason behind this sparking? Would it have been better to connect both chargers to AC first, and only then completing the DC circuit to the battery?

FWIW the BMS was configured to not allow charging when I turned on the chargers. My only theory so far is that the first charger (the one connected to AC) started feeding DC into the second charger, overwhelming it somehow. The chargers have diodes in them though, so AFAIK it shouldn't be a problem to parallel connect them.

Any advice appreciated.

 

[Browse]

Likely a capacitor discharge of something like that. You should be able to parallel outputs of chargers, but the DC side should be fully discharged before connecting anything.

 

[hwy17]

More details about the charger? Model number?

 

[Jalle19]

Likely a capacitor discharge of something like that. You should be able to parallel outputs of chargers, but the DC side should be fully discharged before connecting anything.

It's this one: https://www.meanwelldirect.co.uk/wp-content/uploads/sites/55/2018/04/r401r401_3.pdf I updated the first post to include the full make and model

but the DC side should be fully discharged before connecting anything.

What do you mean by "fully discharged"?

 

[Browse]

It's this one: https://www.meanwelldirect.co.uk/wp-content/uploads/sites/55/2018/04/r401r401_3.pdf I updated the first post to include the full make and model



What do you mean by "fully discharged"?

I know that my Growatt inverter retains voltage on the busbars of my battery rack (after the batteries are turned off) until the capacitors bleed off. It can take an hour or more to see the voltage go back down near zero. I'm assuming most chargers keep some voltage on the DC side for a bit but I could be wrong. You can check this with a voltmeter.

 

[DJSmiley]

In the datasheets I can't find anything on supporting parallel (and thus allowing backfeeding which basicly happens when a single psu is powered on)

Also, as far as I can find, they are power supplies, not chargers. And not all power supplies can handle backfeeding.

 

[Texas-Mark]

In the datasheets I can't find anything on supporting parallel

Why would you? Having two in parallel is really no different than having one connected to a battery. However, whether or not a charger likes to be connected to a battery (or another charger) when not plugged into AC is another story.

I have some PowerMax charger/converters that do strange things when connected to a battery but not AC (like the fan runs when it does not need to even though it's not even connected to AC). But the units still work fine.

Now, I can see some strange things happening if two chargers are connected in parallel, but not connected to a battery. The voltages they would sense from each other might cause them to do strange things. But as long as there is a battery load, I don't see an issue (unless the battery BMS opens and the previous scenario happens).

 

[Browse]

That model doesn't look like it has active current sharing. Some of their models do and will list it on the data sheet:

https://www.meanwell.com/Upload/PDF/RSP-1000/RSP-1000-SPEC.PDF

 

[Jalle19]

Now, I can see some strange things happening if two chargers are connected in parallel, but not connected to a battery. The voltages they would sense from each other might cause them to do strange things. But as long as there is a battery load, I don't see an issue (unless the battery BMS opens and the previous scenario happens).

Okay, so next time I try something I should make sure the chargers have somewhere to put the power they put out (i.e. ensure the BMS is accepting charge)?

I have some PowerMax charger/converters that do strange things when connected to a battery but not AC (like the fan runs when it does not need to even though it's not even connected to AC). But the units still work fine.

I have done this (connecting a battery to the DC terminals on the charger, without the charger being plugged into AC), it produces a fairly big spark at the terminal due to inrush current, then the fan turns on and the LED on the charger turns green. Doesn't harm the device as far as I can tell, which is why I was surprised a second charger (acting as a battery in a sense) could damage a second charger.

@Browse according to https://www.meanwelldirect.co.uk/glossary/what-is-current-sharing/ , active current sharing is a fancy feature that I don't particularly need (the "brute-force" way works just fine).

 

[Jalle19]

Anyway, is the general consensus that everything should work as long as both chargers are connected to AC before connecting the DC side to a battery?

 

[hwy17]

The block diagram for these is a bit different than the Mean Well supplies I have used like these so I don't know.

I think it's slightly concerning that they don't call it a constant current supply with a constant current output graph specification.