Precharge with regular incandescent light bulb?

[DonnieT]

I have a new 6000xp I’ll be connecting to a diy 314ah battery this week can I just use a regular 60w incandescent light bulb to Precharge? I’ve seen some you tube videos but thought I’d ask the pros here before I cook my new inverter

 

[jorby]

I just measured a random 60w bulb at 16 ohms cold. That will be fine. At four amps it will be a small spark.

 

[timselectric]

I have a new 6000xp I’ll be connecting to a diy 314ah battery this week can I just use a regular 60w incandescent light bulb to Precharge? I’ve seen some you tube videos but thought I’d ask the pros here before I cook my new inverter

Sure can.

 

[DonnieT]

I just measured a random 60w bulb at 16 ohms cold. That will be fine. At four amps it will be a small spark.

I found one 130v 60w bulb that read 23.8 ohm I had a 250w measured 5.5

 

[jorby]

I found one 130v 60w bulb that read 23.8 ohm I had a 250w measured 5.5

I measured a 40w at 26 ohms. Those 130v bulbs last longer because they don't run as hot, but make less lumens than the "standard" ones. I am sure the w/lumen efficiency is lower because of the more orange light they make. I only have one incandescent in use for the original purpose anywhere in my house and it seldom used. There are a few twisty fluorescent lamps that will eventually die and be replaced with led. I keep the Incandescent for inverter load testing. Impressive @ 3kw.

 

[740GLE]

Any standard 120v ac incandescent bulb will have plenty of resistance to handle the inrush.

 

[ricardocello]

Any standard 120v ac incandescent bulb will have plenty of resistance to handle the inrush.

I've used that exact lightbulb and base in the past, and they work great.

Since I've added the chargeverter to the system, I just use that instead now.
Just plug it in, wait 10 seconds, and unplug. Turn on battery breakers.

 

[Supervstech]

I have a new 6000xp I’ll be connecting to a diy 314ah battery this week can I just use a regular 60w incandescent light bulb to Precharge? I’ve seen some you tube videos but thought I’d ask the pros here before I cook my new inverter

Yup, and the cool part is, when the bulb dims, the bank is charged and ready to turn on the battery.

 

[JohnV2]

Thanks for the responses above. Could I use this 12V-60V LED bulb as a precharge resistor between the 14.3kWh PowerPRo and 6000XP? I would hope then to also use these 12V bulbs in other projects:

12V-60V LED Light Bulb E26 Low Voltage, Not for 120V, 3000K Warm Light Color, 3W LED Equivalent 25W Lamp, Medium Screw Base, 12V 24V 32V 36V 48V for Camping Light, RV Bulb, Off Grid Power, 2 Pack

 

[hwy17]

LED bulb not so good for precharge I think. Maybe if the inverter has no auto power on but it will be a very slow precharge.

 

[LakeHouse]

Thanks for the responses above. Could I use this 12V-60V LED bulb as a precharge resistor between the 14.3kWh PowerPRo and 6000XP? I would hope then to also use these 12V bulbs in other projects:

12V-60V LED Light Bulb E26 Low Voltage, Not for 120V, 3000K Warm Light Color, 3W LED Equivalent 25W Lamp, Medium Screw Base, 12V 24V 32V 36V 48V for Camping Light, RV Bulb, Off Grid Power, 2 Pack

Probably not. And if it did, the precharge would take a very long time. If there's any other load besides charging the inverter's capacitors you would be fighting a losing battle: That 3W bulb at 54V is only going to pass 0.05A, so you'd better hope every bit of it is going to the capacitors... But it probably isn't.

Maybe if you hooked 20 of them in parallel. But there are easier ways to do it.

 

[SouthernSolar]

I have an 24 ohm 100 watt resistor I use to precharge capacitors when hooking up inverters and battery chargers. Light bulb works, just the resister a lot less fragile.

 

[Quattrohead]

It has to be an old fashioned incandescent lamp or filament lamp.
You can't use a 12 volt because it will blow up but you could use a regular domestic 120 volt lamp at say 40 to 100 Watts, it will slowly start to glow as it allows more current through to charge the caps.
When it stops getting any brighter, you are good to go.

 

[LakeHouse]

You can't use a 12 volt because it will blow up but you could use a regular domestic 120 volt lamp at say 40 to 100 Watts, it will slowly start to glow as it allows more current through to charge the caps.
When it stops getting any brighter, you are good to go.

It's the opposite of this. It should glow most brightly (though still somewhat dim) initially and taper off to nothing. Voltage (and thus current) across the bulb is high initially and tapers off to zero Volts (and zero current).
If the bulb doesn't go out, there's a problem somewhere.

 

[hwy17]

When it stops getting any brighter, you are good to go.

Not that we have to nitpick every single little thing here but since of course we do... My precharge bulbs reach a peak brightness and then taper off.

 

[Skypower]

Just used a gauge lamp for a 12 volt 3K inverter. Amazing how fast a little bulb goes bright to dim.

 

[Backyard]

You want the voltage of the bulb to be at or greater then your battery voltage. Reason being, when the capacitors are fully discharged they look like a short from the perspective of the battery. So, the full voltage of the battery will be across the bulb when first hooked up. When the capacitors charge the voltage difference will drop and the bulb will start to dim.

If the bulb dims but doesn't fully go out, then there is a phantom load or the inverter is drawing power from the capacitors keeping them from fully charging and thus allowing the bulb to go out. If this is the case then a higher wattage bulb might be needed. If the bulb is dimly lit you might be ok to just stop there and hook directly up. The voltage might be close enough to not cause issues

When you have the bulb bypassing the contractor, fuse, switch or breaker to charge the capacitors. You can put your meter on the inverter battery terminals and watch the voltage climb. It will give you a better understanding of the voltage relationship between capacitors and bulb brightness

 

[740GLE]

If the bulb is dim (or anything after say 5 seconds) that means very little current is flowing meaning little voltage difference between the battery and inverter, so connect the mains and you’re good.

 

[BerndL]

I never realized it's not just terminal sparks that can cause a problem.
What happens if you turn your battery off without disconnecting the inverter, then turn it back on?
Do you still get a very high, potentially fuse-popping rush of current?

Another argument for good 48v batteries with built-in precharge circuits, I guess.

 

[Supervstech]

I never realized it's not just terminal sparks that can cause a problem.
What happens if you turn your battery off without disconnecting, then turn it back on?
Do you still get a very high, potentially fuse-popping rush of current?

Another argument for good 48v batteries with built-in precharge circuits, I guess.

If you shut off the battery connection for an appreciable time, yes, precharging is needed. But it needs to be off for more than a few minutes...

 

[SouthernSolar]

My “automatic” pre-charge rig I just made Two power resisters and a 3 amp fuse under the black tape, hooked to a Shelly wifi relay. I can pre charge my inverter before turning on the battery switch,

 

[hwy17]

What happens if you turn your battery off without disconnecting, the inverter then turn it back on?

I set my DIY batteries to never auto recover the discharge circuit after entering protection mode. Which should be an extremely rare event anyway.

 

[TM48]

Thanks for the responses above. Could I use this 12V-60V LED bulb as a precharge resistor between the 14.3kWh PowerPRo and 6000XP? I would hope then to also use these 12V bulbs in other projects:

12V-60V LED Light Bulb E26 Low Voltage, Not for 120V, 3000K Warm Light Color, 3W LED Equivalent 25W Lamp, Medium Screw Base, 12V 24V 32V 36V 48V for Camping Light, RV Bulb, Off Grid Power, 2 Pack

No need... the powerpro has precharge built in.

 

[Zwy]

This is from another thread and later in the video it shows the precharge circuit charging the capacitors.

Post in thread 'Here we go again - upgrades plus new install'

May 10, 2025

That's the plan here, too. I suspect mine will go both ways depending on the time of year and how much I'm doing in the shop. I still need to trench in the connection between the two. And I need to figure out how you rigged your pre-charge resistor so that a light comes on when the capacitors are charged. Didn't I see something like that in your video? At the very least set it up with a push button. My todo list is never-ending. But that's a good thing - keeps me from getting bored.

Wire it at the main switch. Yes, it is in the video. I did the precharge on the negative...

• Zwy

• 

I used a 48V forklift light bulb. 12V bulbs can be used, just wire them in series but the cost of 4 bulbs and 4 sockets would probably be higher than a single 48V forklift battery and socket.

I had used resistors in the past but have been switching over to light bulbs. No guessing, you know when the bulb goes out the capacitors are fully charged.

 

[Quattrohead]

Not that we have to nitpick every single little thing here but since of course we do... My precharge bulbs reach a peak brightness and then taper off.

Yep I arse about faced that one