Help with pre charging capacitors

Hi, hope someone can help me out.

Purchased a 12v, 1000 watt inverter, watched the video on pre-charging inverter and purchased a 25 ohm 50 watt resistor from sourcing map on amazon but even after holding it to negative terminal on lead acid battery for upwards of 10 seconds I'm still getting a spark. Very new to all of this and not sure why I'm still getting a spark, did I get the wrong resistor- it's called a wirewound resistor.
I know those with higher powered systems will know it's a reasonably small spark being a 12v system but I'd still like to eliminate it if possible, thanks!

25Ω is a bit high for 12V system. Try 30 seconds. You need to immediately make the connection. Inverter obviously must be off. If there's anything powered by the 12V system, it needs to be isolated as well or it will gobble the juice you're trying to send to the capacitors.

You could also break the eraser end off a #2 pencil and sharpen both ends. Use the pencil lead as a resistor. That's about 6Ω.

Thanks a lot! Okay I'll try longer with existing resistor and then something lower like suggested. I was testing the inverter with my 12v car battery (with engine running) so will that be why it's not working? How else do I get around that as would prefer to have engine running until I have thought about a different power source.
I kinda thought you're not supposed to have inverter connected then start battery - is that also the case? Thanks.

Since this is a test, make the connection with the car off and leave the car off.

With a car running, that will be pushing current into and out of the capacitor bank of the inverter because of the alternator pulsing. There will always be a spark even if nearly fully charged. 25 ohms is only a half amp maximum at complete capacitor discharge. 6 ohms is more appropriate, 2A isn't going to bother anything.

Thanks!
Okay I think I follow, by me connecting it up with the alternator running its charging and then discharging capacitors so can't properly pre charge whereas if battery wasn't connected it would work.
I'll try the 6 ohm resistor when I can but if I being told I'll always get a spark with this method of connecting up maybe I'll just need to live with the spark for the time being and maybe no need to even use the resistor, I know in the video I watched on pre-charging Will Prowse suggested not bothering using resistor with a 12v system.

I use a 100W incandescent (not LED or fluorescent) light bulb. When the bulb stops glowing the caps are charged.

Amazing how long my 48V 2500W UPS can light that bulb.

Delmar said:

I use a 100W incandescent (not LED or fluorescent) light bulb. When the bulb stops glowing the caps are charged.

Amazing how long my 48V 2500W UPS can light that bulb.

Click to expand...

Hey i'm in a similar situation with a sunpowergold 6000w INV and a Jackiper 48v battery ... the battery is currently discharged to 12v do i need to connect the resistor between the batt and INV ? can i use the lightbulb?