Just blew both 200a Class T fuses after precharging with a 25w / 30ohm resistor…?

Hi all,

After watching Will’s many videos and searching on the forum, I’m still perplexed by what’s happened with this system today. I had two brand new EG4 6000ex’s installed this morning, with 8x Rich Solar 12v/200ah batteries wired in two parallel 48v banks (batteries were already here from previous build, otherwise I would have opted for 48v units instead).

After spending all day wiring it all up, it was finally time to power it on. The electrician jumpered the battery switch posts with the resistor (25w/30ohm) for 5-8 seconds, at which point he stopped due to the resistor getting too hot to hold.

When he activated the battery switch, we were greeted by sparks within the switch and found that neither inverter would light up. Further inspection would show each of the 200a Class T fuses blown.

Our guess is that we didn’t precharge long enough? In all the YouTube viewing I’ve done on the subject, 5-8 seconds seemed like enough time. Perhaps we were wrong?

A couple questions for you guys:

1. Is it because we have two inverters, both with caps that are making the precharge take longer?

2. Are the fuses large enough at 200a?

3. I’m still confused as to how with the amount of precharging we did, there was still enough current to pop two 200a fuses?

4. If 5-8 seconds wasn’t enough, how much is? Should I measure amps with a DC clamp meter and precharge til the current reads 0?

5. Should I be worried about any potential damage to these virgin inverters?

Thanks in advance. I’m guessing this is a super elementary question for all the more experienced folks here.

When they jumpered the switch with the resistor you should have seen the inverters power up, at least my TP6048 did.
Where did they jumper the resistor?
Are the inverters paralleled or each feeding a separate panel?

Jumper should have been something like the blue line below.

Thanks for the response. He literally jumpered from one post inside the switch to the other post inside the switch— essentially turning the switch on by way of the resistor. So both inverters were getting current at once.

Neither inverter lighted up at any time.

Check for a short somewhere. If he had to stop because the resistor got hot, then it obviously wasn't done charging... Assuming it was charging. 5-8 seconds would seem like long enough.

dhy4buva said:

Hi all,

After watching Will’s many videos and searching on the forum, I’m still perplexed by what’s happened with this system today. I had two brand new EG4 6000ex’s installed this morning, with 8x Rich Solar 12v/200ah batteries wired in two parallel 48v banks (batteries were already here from previous build, otherwise I would have opted for 48v units instead).

After spending all day wiring it all up, it was finally time to power it on. The electrician jumpered the battery switch posts with the resistor (25w/30ohm) for 5-8 seconds, at which point he stopped due to the resistor getting too hot to hold.

Click to expand...

this absolutely positively shouldn't have happened.

Was the inverter power switch pushhed in (on) when you tried to precharge?

Did either inverter have a load on the AC side?

dhy4buva said:

View attachment 154016

Thanks for the response. He literally jumpered from one post inside the switch to the other post inside the switch— essentially turning the switch on by way of the resistor. So both inverters were getting current at once.

Neither inverter lighted up at any time.

Click to expand...

That should have worked just fine too, something else is majorly wrong here.

What was the voltage at the switch before the buss bar?
What brand are those class Ts?
Those batteries can be wired in series?

sunshine_eggo said:

this absolutely positively shouldn't have happened.

Click to expand...

Seems possible, I am not sure why you say that. The wattage would be near 90W going through the resistor at the start.
Maybe I am missing something.

As a side note, it is recommended to mount those inverters on a non-combustible surface. It looks like from the pics they are mounted directly to plywood.

That is very odd it looks like the positive and negative are reversed, need to go look at mine to be sure.

Looked everything over one more time and also do not see any parallel cables.

robby said:

Seems possible, I am not sure why you say that. The wattage would be near 90W going through the resistor at the start.
Maybe I am missing something.

Click to expand...

That 90W should be the beginning of a very short transient down to zero watts as the battery and capacitor voltages equalize. My precharge circuit takes about a second to get the inverter voltage to within 0.5V of the battery voltage. My resistor is way undersized compared to this one, and it doesn't even get warm to the touch, let alone hot.
For a 25W resistor to get too hot to hold in 5-8 seconds, as OP notes, it was probably at 90W that entire time. Which, as @sunshine_eggo says, should not happen.
There's got to be a short somewhere.

When I pre charge my XW with a lightbulb it gets hot enough to feel the heat in your hand for .5 seconds and then cools.

kromc5 said:

That is very odd it looks like the positive and negative are reversed, need to go look at mine to be sure.

Click to expand...

Did you look at yours yet?

If the parallel diagram in the manual is correct:



Oops.

Am I crazy or does it look like the positive and negative are reversed? In that diagram @v_green57 posted and the couple I saw online have the negative and positive entering reverse of what that installation shows of @dhy4buva 's., or at least entering the inverter reversed.

v_green57 said:

Did you look at yours yet?

If the parallel diagram in the manual is correct:



Oops.

Click to expand...

They are reversed, I have been up working on the computer all night and just went down to check.
I checked my resistor it's 100w 20ohm but has never gotten warm on the 12k, eg4, etc.

Are they not clearly labelled? Just wondering how that could happen for the most crucial connections. It's possible then the EG4s are indeed damaged if they don't have built-in reverse polarity protection.

? I think you guys are right about the reversed wires. I’m a bit in shock that this happened. Everyone makes mistakes, I know.

Are these brand new units toast? Or is there a chance the fuses saved them? Or perhaps an internal fail safe?

I’m going back out tomorrow to check the terminal markings, but for now, I’m going to do some breathing exercises.

Thanks all, you’ve been so helpful!

v_green57 said:

Did you look at yours yet?

If the parallel diagram in the manual is correct:

View attachment 154030

Oops.

Click to expand...

Good catch