What size resistor?

johnskdyvn · May 12, 2023

Hello,
Somewhere on the forums i saw the size resistor i would need to precharge my 48v 3000w Growatt. Now, I can't find it anywhere. Does anybody recall the resistor i would need so i don't have to have an unintended fireworks show in my workshop/solar shed?

If not, how about the size of lightbulb i would need to do the same function?

Thanks again everybody!

sunshine_eggo · May 12, 2023

#2 pencil exposed at both ends. ABout 6Ω and can handle the power.

Pretty much any 120VAC incandescent/halogen light bulb. @48v, you can never provide enough current to blow a 120VAC bulb.

johnskdyvn · May 12, 2023

sunshine_eggo said:
#2 pencil exposed at both ends. ABout 6Ω and can handle the power.

Pretty much any 120VAC incandescent/halogen light bulb. @48v, you can never provide enough current to blow a 120VAC bulb.

I have this handy. Will this work? Thank you!

Bud Martin · May 12, 2023

Correction:
BTW, I made typo.
300W/130V = 2.3A, 130V/2.3A = 56 Ohms, 56 Ohms/10 = 5.6 Ohms (3.73 Ohms if 15 is used).

~~300W 130V incandescent lamp will have hot resistance of around 300W/130V = 2.30 Ohms, the cold resistance will be about 2.30/15 = 0.15 Ohms,~~ you can verify that by using your Ohm meter.

27 Ohms 25W will be fine, the charging will happen so fast that the resistor will not heat up and exceed the Wattage rating, just to make to pre-charge with in the inverter power switch is in the OFF position.

sunshine_eggo · May 12, 2023

Bud Martin said:
300W 130V incandescent lamp will have hot resistance of around 300W/130V = 2.30 Ohms, the cold resistance will be about 2.30/15 = 0.15 Ohms, you can verify that by using your Ohm meter.
27 Ohms 25W will be fine, the charging will happen so fast that the resistor will not heat up and exceed the Wattage rating, just to make to pre-charge with in the inverter power switch is in the OFF position.

In other words, that bulb will work fine...

johnskdyvn · May 12, 2023

sunshine_eggo said:
In other words, that bulb will work fine...

Thank you to you both. One wire from battery terminal to “base” of bulb, and other wire from inverter to “brass color” part of bulb (the screw in part of bulb)? Sorry, I don’t know the nomenclature of a lightbulb ?

sunshine_eggo · May 12, 2023

johnskdyvn · May 12, 2023

sunshine_eggo said:
View attachment 148946

Sweet! You rock!

JWLV · May 12, 2023

Creative electronics hackery!

efficientPV · May 13, 2023

Bud Martin said:
300W 130V incandescent lamp will have hot resistance of around 300W/130V = 2.30 Ohms, the cold resistance will be about 2.30/15 = 0.15 Ohms, you can verify that by using your Ohm meter.
27 Ohms 25W will be fine, the charging will happen so fast that the resistor will not heat up and exceed the Wattage rating, just to make to pre-charge with in the inverter power switch is in the OFF position.

Where did you come up with 15. Typically the resistance change is 7 to 1. Most I've ever seen is 10. A 100W 120V lamp is more than sufficient. Hard to find lamps these days cheap. I always pick them up at garage sales in the free bin.

Bud Martin · May 13, 2023

Typical is 10 ~ 15.
BTW, I made typo.
300W/130V = 2.3A, 130V/2.3A = 56 Ohms hot R, 56 Ohms/10 = 5.6 Ohms (3.73 ohms if 15 is used).

https://www.edn.com/hot-resistance-versus-cold-resistance/

What size resistor?

johnskdyvn

New Member

sunshine_eggo

Happy Breffast!

johnskdyvn

New Member

Bud Martin

Solar Wizard

sunshine_eggo

Happy Breffast!

johnskdyvn

New Member

sunshine_eggo

Happy Breffast!

johnskdyvn

New Member

JWLV

-.-. --.-

efficientPV

Solar Addict

Bud Martin

Solar Wizard

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