Pre-charging inverter capacitors with a lead pencil?

[curiouscarbon]

Also keep in mind that the wattage rating doesn't mean too much. The max power will be simply Volts*Volts/Amps, but that will only pass through the resistor for a fraction of a second. I'm only guessing, but if the math says it will peak at 100W, you could easily get by with a 50W resistor.

good point; current will only flow for a small moment, under normal circumstances

a 50W resistor ought to be perfectly sufficient for manual precharging

if resistor gets hot, disconnect and wait

 

[Steve Fractals]

Hi guys, I've just purchased an inverter (MPP 6048MT) that can be used battery-less. Given it can be used battery-less I'm guessing it can startup from either generator/grid or solar and does indeed have a generator autostart feature.

Does this mean I don't need pre-charge if attaching a battery if the invertor is set to utility or solar as first priority?

 

[Supervstech]

Hi guys, I've just purchased an inverter (MPP 6048MT) that can be used battery-less. Given it can be used battery-less I'm guessing it can startup from either generator/grid or solar and does indeed have a generator autostart feature.

Does this mean I don't need pre-charge if attaching a battery if the invertor is set to utility or solar as first priority?

Only batteries need precharge… solar will only output what they produce, so it is a constrained flow anyway.

 

[hyberlut]

I was told by the guy at Watts 25/7 Growatt dealer that I could pre-charge my inverter capacitors with a lead pencil as my resistor, anyone ever heard of this?

I watched a video yesterday of a guy demonstrating this to pre-charge the caps in his 48V inverter. It worked, no sparks and not enough juice for long enough to be dangerous.

From what I've read (I think Will Prowse said this), it's essential to do on a 48V system, good idea on 24V and not necessary on 12V systems.

Yesterday I had to disconnect and rewire my inverter, 12V system. When I went to connect the inverter, yeah a little spark. In the tight quarters I couldn't get the terminal bolt in just yet, so the wires touched and left the battery terminal several times before I could finally get the bolt in. No sparks, so I guess the caps hold their charge for a bit, not sure for how long, probably not more than 30 seconds I would guess.

 

[OilCan]

Well after viewing some EG4 battery inspections on YouTube, they already have a fairly large sized pre-charge resistor built-in so I didn't bother installing that circuit. Both Growatts started up just fine on my new install.

 

[Supervstech]

Well after viewing some EG4 battery inspections on YouTube, they already have a fairly large sized pre-charge resistor built-in so I didn't bother installing that circuit. Both Growatts started up just fine on my new install.

Keep in mind you have to follow the startup procedure to use the charge circuit.

 

[OilCan]

Keep in mind you have to follow the startup procedure to use the charge circuit.

If there is a particular startup procedure to enable the pre-charge circuit it certainly is not documented in any of my manuals for EG4 and Growatt. My guess would be if the Growatt is Off and in Standby, then once the battery is Enabled then the internal circuitry in the battery will do a momentary limit of startup current. Let me know otherwise, thanks for commenting!

 

[Supervstech]

If there is a particular startup procedure to enable the pre-charge circuit it certainly is not documented in any of my manuals for EG4 and Growatt. My guess would be if the Growatt is Off and in Standby, then once the battery is Enabled then the internal circuitry in the battery will do a momentary limit of startup current. Let me know otherwise, thanks for commenting!

Will has done videos of the ra k mount batteries showing the procedure.