What ohm resistor to charge capacitor & max voltage for pannels with Growats 3K system.

[dajale]

Quick question I have noticed multiple folks using a resistor to stop sparks when connecting a battery to an all-in-one system. I am connecting 4 x 200AH batteries what resistance should I use to charge the capacitors and stop sparking?

Another quick one I have 6 x 200 Wat panels I plan to connect to a Growatt 24V SPF 3000TL LVM will that be too much or do I need to split them up? What is the maximum I can have attached to this unit?

Really excited about getting into solar myself.

 

[Bud Martin]

25 Ohms 50W Inverter capacitor bank pre-charge resistor will be fine.

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As far as the panel wiring configuration, you will need the spec (Voc, Vmp, Imp, Isc) of the panel and the max PV Input Voltage limit of the SCC because you cannot go over the Input limit of the SCC, you also need to factor in about +15% for cold weather Voltage.

So get the spec of the panel and the SCC.

 

[NHRenewables]

just use an old incandescent lightbulb… it is just a resistor after all…

 

[Tecnodave]

The advantage of using a incandescent bulb is it will function as a charge state indicator. Im using a 32 volt marine 25 watt bulb on my inverter start switch. When I turn on the pre-charge switch the bulb will glow brightly for about 8-15 seconds then start to dim, at that point the capacitors are charged enough to avoid the huge inrush of current that the capacitors need. Dropping resistor with built in metering. A 120 volt bulb could also be used, 100 watts or so.

 

[JRUD]

just use an old incandescent lightbulb… it is just a resistor after all…

Months ago I used a pre-charge resistor as recommended by Will Prowse and others . Worked fine. No spark. My question is .... If i ever disconnect or even switch off my batteries for any period of time would I have to use that resistor again because the capacitors have slowly discharged? Why I ask is I recently I had to disconnect my batteries for a few hours. When I plugged my Anderson connector back together I noticed a small spark. Seems crazy to have a quick, safe disconnect and still have to unbolt cables and use that resistor before you can turn things on again. FYI, My system is kinda small (100AH, 24V Growatt)

 

[Roswell Bob]

Months ago I used a pre-charge resistor as recommended by Will Prowse and others . Worked fine. No spark. My question is .... If i ever disconnect or even switch off my batteries for any period of time would I have to use that resistor again because the capacitors have slowly discharged? Why I ask is I recently I had to disconnect my batteries for a few hours. When I plugged my Anderson connector back together I noticed a small spark. Seems crazy to have a quick, safe disconnect and still have to unbolt cables and use that resistor before you can turn things on again. FYI, My system is kinda small (100AH, 24V Growatt)

I would think the capacitors would discharge fairly quickly. It is customary to run a switching power supply off of the DC bus. When the input DC is removed the switcher tends to discharge the bus quite low.

 

[Tecnodave]

On my systems I have a Blue Seas 350 amp. battery shutoff switch to depower the inverters and a smaller push button switch wired directly across the main cutoff switch. The small switch turns on the bulb in series with the inverter so inverter current is limited by the resistance of the bulb. Currently im using an 12 volt automobile stop light bulb type 1073 which draws about 2.3 amps in series with a 8.6 ohm resistor. This precharges the capacitors in the inverter and thus prevents a huge current inflow as the capacitors charge. Each inverter has such a precharge switch on each battery bank. I use two main banks of batteries that are dissimilar enough that they don't play together well and several different inverters for different kinds of loads. The bigger inverters run things like my water pump and mig welder but emit far more EMI/RFI that i would rather not have in my environment. I use Exeltech high frequency ultra low noise inverters for every day use as i do not enjoy inverter switching noise in my high end stereo sound system.

Part of the system is 100% redundancy so that no matter what, I do have electrical power

In my case my power company is very unreliable as i am down the end of a long private road and my POCO service is only 30 amps 120 volt installed in the 1920’s and I have long periods with no service, not a priority for the power company when they have 55,000 customers with no power. Upgrading the power to 240 volt 200 amps would be in the 10‘s of thousands so I have a complete off grid system even though I do have POCO power but the cost of the entire off grid system is far less than a power upgrade besides the building inspectors cannot even see my house as they are not allowed to pass a locked gate here. And i do not need them poking their nose in my business.....

 

[NHRenewables]

Devices are usually designed to self discharge for the benefit of safety, so yes, more than a couple of minutes, the safe bet is to precharge with your resistor of choice.