Small test fixture

[HarryN]

Sometimes it is easier to show people things in photos than to describe them.

So I made a little test fixture from left over parts, nothing fancy.

In this case, some people asked about methods of dealing with pre-charging the capacitors on the input stage of inverters, and I had suggested that they try to just have a small solar panel connected to it as one approach.

So here are a few pics.

 

[HarryN]

Just a basic 12 volt AGM battery with an in line fuse and 10 awg wire.

 

[HarryN]

Solar panel on the driveway ( This was taken in relatively poor lighting conditions )

It is I think a 140 watt panel, nominal Vmp 18 volts, Voc ~ 22 volts.

 

[HarryN]

Test fixture:

- Fuse block

- Trimetic for measurements
- On the far left is the WiFi module that goes along with the trimetic to broadcast the info to cell phone or tablet

- The black box on top is a typical 12 volt / 1100 watt inverter that is needing to be pre-charged. The black and red pair of 10 awg are feeding the inverter terminal from a 30 amp fuse. This is just for testing things, not for full operation of the inverter.

Solar panel directly fed into the test fixture without any battery connection. The orange wire with some yellow tape on the left side is the (+ ) wire directly from the solar panel.

- The white wire with red tape on it on the lower right side of the fuse block is the 12 volt battery (+) connection. In this step, the fuse position is removed to block the connection to the battery.
_____________

The solar panel current output is naturally limiting the current flow because it cannot produce more than ~ 10 amps, no matter what.

Within a very short time (faster than I can turn the display on ), the test fixture ( and inverter capacitors ) are charged up to the real time Voc of the solar panel. ~ 19 volts since it is overcast out.

 

[HarryN]

Same set up, but now I added the fuse to connect the fuse block to the 12 volt battery.

The battery of course can absorb far more power than the solar panel can output, so the entire system pulls down to the Vbat ~ 12 volts.

The reverse of course does not work. If I try to pre-charge the inverter by just feeding from the batter pack, the 30 amp fuses blow.

Using the solar panel to pre-charge solves the problem. I don't know what the actual current is because it happened too fast for this setup, but it didn't blow the 30 amp fuses.

 

[HarryN]

Some photos that I wanted to capture were hit by a funny snag. The camera shutter speed is much faster than the display, so sometimes only 1 digit was showing in a photo that could have been helpful.

Let me know if you need more info.

 

[toms]

I’d be curious to see the inrush current trace of that inverter - i’ve never bothered with precharge for 12V inverters.

 

[HarryN]

I’d be curious to see the inrush current trace of that inverter - i’ve never bothered with precharge for 12V inverters.

Thanks for looking at the setup.

My goal was to just show a proof of concept for people to see how a solar panel can be used to pre-charge "any" inverter and potentially simplify the process vs adding in resistors and other circuits.

That one AGM battery will power up any inverter that I have ever attached to it just fine. The main reason to pre-charge in general is to protect the BMS from tripping in Li batteries, at least in my mind. I have most definitely seen that happen on a Victron 3000 / 12 with 3 Li batteries in parallel. It tripped just one of the battery's BMS so the system seemed to work, just not correctly.

4 of those Lifeline AGMs in series can power up a Victron quatro 5000 / 48 at my shop with no problem. 4 battleborns in the same use will trip without a pre-charge. It is easy to re-set though by turning the breaker on / off a few times to re-set the BMS. Some people don't like to do this.

_______________

I used components that I had sitting around so that is why it is built from a bluesea fuse block, bogart SOC monitor and 10 awg wire. The limitation is that this means that the max fuse size rating is 30 amps, and I have a 30 amp in line fuse at the battery, and then 30 amp fuses in the fuse block locations for power coming in, and at the location feeding the inverter. So quite a bit less than you would normally have for a 1000 watt / 12 volt inverter.

The bogart monitor tracks voltage, current and then turns this into SOC, but only displays one at a time. (unless you look at the wireless display ) so my plan was to have it on the "current monitor" display and watch what happens. What really happened is that the surge when not pre-charged caused the bogart to switch what was being displayed, so it went into somewhat of a fault mode. This eliminated my ability to watch it real time - at least with this setup.

So this limited this setup to just act as a go / no go guage - "will it blow a 30 amp fuse or not as an "indicator" of the inrush current".

Without the solar panel pre-charging the inverter - the 30 amp fuse blew instantly.

With the solar panel pre-charge - it didn't.


This panel is a nominal 18 volt Vmp panel, but it could also be used to pre-charge a 24 volt system. For higher voltage packs, a different panel can be used that more closely matches that need. The size / power output of the panel does not matter either as it is just to trickle it in there.

 

[toms]

Thanks for looking at the setup.

My goal was to just show a proof of concept for people to see how a solar panel can be used to pre-charge "any" inverter and potentially simplify the process vs adding in resistors and other circuits.

That one AGM battery will power up any inverter that I have ever attached to it just fine. The main reason to pre-charge in general is to protect the BMS from tripping in Li batteries, at least in my mind. I have most definitely seen that happen on a Victron 3000 / 12 with 3 Li batteries in parallel. It tripped just one of the battery's BMS so the system seemed to work, just not correctly.

4 of those Lifeline AGMs in series can power up a Victron quatro 5000 / 48 at my shop with no problem. 4 battleborns in the same use will trip without a pre-charge. It is easy to re-set though by turning the breaker on / off a few times to re-set the BMS. Some people don't like to do this.

_______________

I used components that I had sitting around so that is why it is built from a bluesea fuse block, bogart SOC monitor and 10 awg wire. The limitation is that this means that the max fuse size rating is 30 amps, and I have a 30 amp in line fuse at the battery, and then 30 amp fuses in the fuse block locations for power coming in, and at the location feeding the inverter. So quite a bit less than you would normally have for a 1000 watt / 12 volt inverter.

The bogart monitor tracks voltage, current and then turns this into SOC, but only displays one at a time. (unless you look at the wireless display ) so my plan was to have it on the "current monitor" display and watch what happens. What really happened is that the surge when not pre-charged caused the bogart to switch what was being displayed, so it went into somewhat of a fault mode. This eliminated my ability to watch it real time - at least with this setup.

So this limited this setup to just act as a go / no go guage - "will it blow a 30 amp fuse or not as an "indicator" of the inrush current".

Without the solar panel pre-charging the inverter - the 30 amp fuse blew instantly.

With the solar panel pre-charge - it didn't.


This panel is a nominal 18 volt Vmp panel, but it could also be used to pre-charge a 24 volt system. For higher voltage packs, a different panel can be used that more closely matches that need. The size / power output of the panel does not matter either as it is just to trickle it in there.

I appreciate the time you have put into this, and am trying to get a better understanding. Thanks.

 

[HarryN]

I appreciate the time you have put into this, and am trying to get a better understanding. Thanks.

Anytime - feel free to comment or ask. The electrical part actually didn't take me all that long because I have all of the tools to crimp those non insulated panduit terminals and a heat gun for the heat shrink.

What turned out to be more challenging for me was taking the photos. It was getting late in the day so there actually was not much light on that panel on the driveway. The Bogart uses a fairly low power / but bright display (due to the color chosen ) but it also refreshes the digits more slowly than I thought. About 1/2 of the photos had a digit missing and I missed that detail when taking the pictures.