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Charging my Growatt capacitors

Dr Mark

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Mar 15, 2021
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I have been worried every time I turn off my battery (connected with an Anderson 175) because I do not have an easy way to use a resistor to charge capacitors of my Growatt SPF 3000TL LVM. I do not intend keeping inverter on and seems the best way to turn it off is to disconnect battery (battery has on/off button). I needed to protect the Growatt with a breaker shown where I added the black wire to one post (because resistor would not reach). Now when I turn on or connect battery this breaker will be open, then I can use the resistor to connect top pole to black wire and charge capacitors. I am not sure how important this is to do but it was fun hooking it up. :)

CapBreak.jpg
 
I have been worried every time I turn off my battery (connected with an Anderson 175) because I do not have an easy way to use a resistor to charge capacitors of my Growatt SPF 3000TL LVM. I do not intend keeping inverter on and seems the best way to turn it off is to disconnect battery (battery has on/off button). I needed to protect the Growatt with a breaker shown where I added the black wire to one post (because resistor would not reach). Now when I turn on or connect battery this breaker will be open, then I can use the resistor to connect top pole to black wire and charge capacitors. I am not sure how important this is to do but it was fun hooking it up. :)

View attachment 43678
You can also use Momentary N.O. push button in series with the resistor and then connect it to the circuit.
 
What's a solid state relay?
Kind of like a heavy duty manual switch that can carrier alot of current with no arcing during switching open and closed states. Can be done remotely and with that momentary switch another mentioned here.
 
Kind of like a heavy duty manual switch that can carrier alot of current with no arcing during switching open and closed states. Can be done remotely and with that momentary switch another mentioned here.
Personally I think the push button in combination with a resistor is good enough. Actually even without the push button, that's what I did. Just have to remember to do it...lol. Besides, how often are the capacitors going to need to be pre-charged? As long as something doesn't trigger LVD and disconnects the inverter the capacitors will always be charged.
 
Home Depot...would this $4.49 switch be adequate?

Do you know what the battaery Voltage is? We need that number to calculate the short circuit current based on the resistor value.
Switch is rated 6A? Based on calculation below, it will be fine to use based on current but you need to find out what the DC rating of the switch is, it only shows 125VAC/250VAC, no DC rating shown., I would say it may handle 12VDC (actual Voltage >12VDC), or 24VDC (actual Voltage >24VDC system OK, but not 48V (actual Voltage >48VDC).
For example:
12V system, using 47 Ohms the current will be 12V/47Ohms = 0.25A. Resistor Wattage = 12V * 0.25A = 3W, for safety margin = 6W (5W will be fine).
24V system, using 47 Ohms the current will be 24V/47Ohms = 0.50A. Resistor Wattage = 24V * 0.50A = 12W, for safety margin = 25W.
48V system, using 47 Ohms the current will be 48V/47Ohms =1.00A. Resistor Wattage = 48V * 1.00A = 48W, for safety margin = 100W.
 
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We have discovered some of these all in one inverters will charge the capacitors with AC hooked up, so if you are just disconnecting the battery, then the capacitors should stay fully charged.

You might want to confirm this though.
 
Do you know what the battaery Voltage is? We need that number to calculate the short circuit current based on the resistor value.
For example, a Li-Po battery that may have charge as high as 58v, plus a 25w/30ohm resistor.
Not sure about the capacitor specs for the Growatt.
 
We have discovered some of these all in one inverters will charge the capacitors with AC hooked up, so if you are just disconnecting the battery, then the capacitors should stay fully charged.

You might want to confirm this though.

Oh, I thought AIO goes dead without battery connection.
 
Do you know what the battaery Voltage is? We need that number to calculate the short circuit current based on the resistor value.
Switch is rated 6A? Based on calculation below, it will be fine to use based on current but you need to find out what the DC rating of the switch is, it only shows 125VAC/250VAC, no DC rating shown., I would say it may handle 12VDC (actual Voltage >12VDC), or 24VDC (actual Voltage >24VDC system OK, but not 48V (actual Voltage >48VDC).
For example:
12V system, using 47 Ohms the current will be 12V/47Ohms = 0.25A. Resistor Wattage = 12V * 0.25A = 3W, for safety margin = 6W (5W will be fine).
24V system, using 47 Ohms the current will be 24V/47Ohms = 0.50A. Resistor Wattage = 24V * 0.50A = 12W, for safety margin = 25W.
48V system, using 47 Ohms the current will be 48V/47Ohms =1.00A. Resistor Wattage = 48V * 1.00A = 48W, for safety margin = 100W.

Thanks for the calcs!
 
Nice. I uses a momentary button with a seperate switch to precharge using an NTC thermistor and a power diode to prevent backwards power from the inverrter. A resistor would have worked just as well. with the disconnect off.
 
Personally I think the push button in combination with a resistor is good enough. Actually even without the push button, that's what I did. Just have to remember to do it...lol. Besides, how often are the capacitors going to need to be pre-charged? As long as something doesn't trigger LVD and disconnects the inverter the capacitors will always be charged.
So you are saying that having the battery and AC disconnected for 1 day, 1 week, or 1 month will not be enough time to discharge a capacitor in this type of system? I don't know how quickly capacitors lose their charge. I had a 1 farad cap in my car sound system and I always assumed it was charged and used a resistor to discharge it.
 
So you are saying that having the battery and AC disconnected for 1 day, 1 week, or 1 month will not be enough time to discharge a capacitor in this type of system? I don't know how quickly capacitors lose their charge. I had a 1 farad cap in my car sound system and I always assumed it was charged and used a resistor to discharge it.
No that's not what I said. My point was as long as the battery is connected the capacitors will remain charged unless something triggers a LVD and then the capacitor would need to be pre-charged. How often is that going to happen?

I think inverter caps discharge quickly due to the internal circuitry they are connected to. I had a cheap 1000 watt inverter I was using to test my battery and the capacitors in that thing did not hold a charge.
 
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