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.

 

[HarryN]

Well, we all know how it is. I went out to the garage to clean up the work bench and got distracted.

Started to add on things and make a few changes.

Still - continued to use parts and stuff that I had sitting around, which unfortunately included a 12 volt inverter vs I prefer to do 24 volt stuff, but it is essentially the same. Blame @RV8R - he convinced me that building a 12 volt system isn't a mortal sin.

So it is now sort of evolving into a work bench integrated small power system.....

 

[HarryN]

Still a work in progress.

Photo on the left - The solar panel is for now, sitting in the driveway and a wire running into the garage for power.

Second photo taken on top of the work bench:

- on one side of the board is the 1100 watt inverter. ( not yet wired )
- There are 2 breakers for the batteries ( one for each battery )
- The third breaker is to feed the fuse block. It is rated for ~ 150 amps and cannot be directly connected to this much battery power, so the breaker acts as the primary safety for it.

 

[HarryN]

This photo is the flip side of the board with the various items attached ( reverse of the inverter side )

It will get mounted similar to this but right now is just in place.

In case it isn't obvious, it is under my work bench in the garage. In this location, we could have quite a flood and it would still operate to power the garage fridge or my other tools. (other than needing to put the solar panel somewhere else )

The two batteries are just some Lifeline GPL-27 , 100 amp-hr AGMs that I had, not being used, so they are there mounted in parallel. Each battery feeds in through a blue sea 187 breaker.

There wasn't room for a bus bar, and it is only 2 batteries, so I just joined the breakers with a heavy guage wire.

The fuse block is a 12 position, blue sea fuse block.

The uppper right section is a bogart engineering kit. The white box is their Trimetic monitor for SOC and more advanced features ( only partially wired right now )

Directly under the monitor is the PWM solar controller, which is great for this because of the solar panel position - it started to produce power at 6 am this morning but only gets power part of the day.

Just to the left of the solar controller is the WiFi module. This transmits the info and allows very easy programming via any device with WiFi and no additional software or applications to install.

To the right is the shunt that comes in the kit.

This is the Bogart kit just to make it easy to find. I have no affiliation other than just being a customer.

All Inclusive Kit - Battery Monitor, Solar Charger, WiFi Module & accessories

TM-2030 RV & Off-grid Battery monitor SC-2030 Solar Controller WF-2030 WiFi Smartphone Remote Module Shunt - 500 Amps or 100 Amps shunt TS-2 Battery temperature sensor 35 ft wiring harness serial communication cable. Add solar panels and batteries to make a Solar Generator.

shop.bogartengineering.com

 

[RV8R]

Looks Good @HarryN

It is comforting to see you playing around in the cheap seats of 12vdc ,,, & all that stuff was just laying around collecting dust & now it is collecting sunlight. This kinda reminds me of a few months back when I reinstalled some old but good quality stereo equipment & purchased a $30 Bluetooth receiver so I could use my iPhone seamlessly.

 

[HarryN]

So it continues to grow - but possibly usefully.

I took my most trusted battery charger and added it to the mix.

I use when I need to precisely charge batteries and make them into "matched sets".

Because of how it is built, it can charge 12 or 24 volt setups. Also gives me a handy place to charge batteries.

Not finished wiring it up, but now it is mounted, which really needs to be thought through, because someone in the company must own stock in a copper mine, they are really heavy duty.

Might convert it to 24 volt - which is very simple with this set of parts. Just need to swap out the inverter for a 24 volt version and some minor wiring changes.

 

[featherlite]

My first charger and monitor for my first set of lead acid batteries used the Bogart system, I think Bogart is a great set up for a small lead acid system. IMHO, the literature describing how to properly charge a lead acid battery is outstanding.

 

[HarryN]

Added a blue sea dual 12 / 24 volt USB port, so it continues to be capable of running on either voltage ( other than the inverter is a 12 volt one ). Far right on the inverter side / far left on the DC side in the photos.

There are two solar inputs using SAE ports. Left of the inverter. Right now, only the bottom one is wired, but eventually will act as a sort of combiner for multiple solar panels to plug into.

Wired up the inverter so it is running now. Need to add a 120 vac GFCI outlet.

Also need to add the data wires from the WiFi unit to the SOC monitor and solar charger so that the info is sent over WiFi and not just the display. ( I am happy with the display, just easier to program it using the WiFi )

It works well enough that I charged a tablet from the USB port last night, and today am testing it by running one light in the garage and a small home refrigerator ( 120 vac) just for functional testing. The fridge seems to be pulling about 110 watts when the compressor is running.

I don't yet have the 120 vac - 12 volt DC battery charger hooked up yet. Thinking about getting some alligator clamps for it so it is easy to move between batteries.

The DC wires feeding the inverter are going through the mounting board to the DC side.

All of the power feeds to the Bogart components have their own supply to the fuse block vs the traditional method. It might make sense to combine some of them but for this setup it was just easier for me to do it this way.

I covered up some of the wood working mistakes with green tape until I can put a finish on it to do that.

The green tape on the inverter is just to keep it from being scratched up since I need to work on both sides of it.

 

[2Big2B]

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.

Thanks Harry.

From reading this I realize that I should charge the inverter before attaching to my DYI, BMI protected, wheelchair power supply.

I just ordered a 25w 30ohm cement resistor to have on hand for it.

I am still confused why it is called "Charging", as it seems like exactly the opposite function...

 

[HarryN]

Thanks Harry.

From reading this I realize that I should charge the inverter before attaching to my DYI, BMI protected, wheelchair power supply.

I just ordered a 25w 30ohm cement resistor to have on hand for it.

I am still confused why it is called "Charging", as it seems like exactly the opposite function...

The typical inverter has capacitors on the DC input. The reason is that the internal switching frequency is relatively high so it can exceed the ability of the wire and batteries to deliver power into the switching / coil circuit. The capacitors kind of smooth out the input current flow - effectively spreading out the pulse over time.

Imagine that you have some large capacitors just sitting there and do a hard attachment to a battery - the current flow "pulse" will be very large.

The purpose of "pre-charging" the capacitors" is to spread this out over time.

So the conventional way of doing this is to have a switch or breaker in between the battery pack and the inverter. You pre-charge the inverter caps to bring them roughly to battery voltage and then turn on the switch or breaker.

____________________

if you look at post #`17, you will see the bogart solar charge controller. One of the reasons that I like to use this controller is that it can in fact start from 0 volts on the output and charge up the inverter caps. A lot of solar charge controllers operate off of the battery power and require there to be a useful battery voltage to start up. This can be a real pain operationally.

The other solar controller that boosts the voltage that I suggested will also do this - so no problem either way.

___________

I can pre-charge those caps as well with just a normal 120 vac charger.

_________________

Imagine that for some reason, the BMS has tripped - now you have no useful battery voltage or current to start up the solar charge controller. There might be plenty of sunshine and you cannot get any charging.

The reason for the breaker is that many BMS setups will re-set if the battery is electrically isolated from all other sources of power. That is why I put a breaker on each battery - that way I can re-set the BMS if needed, or for maintenance. Yes these are AGM, but I use the exact same setup for LiFe, so consistency.

____________

Cheating just a little bit, I can also pre-charge the inverter caps even with just that breaker in place. Suppose that you have no method of pre-charging the caps, but have those breakers in place.

Turn on the breaker - BMS might trip, bus some power went into the caps.

Turn breaker off, then back on a couple of times. What I find is that after 3 - 4 x, the caps are charged up enough to make it all work. Not a perfect approach, but it seems to work on battle born batteries and that breaker combo.

_______________
I need to go back and look some more at your thread again to catch up with it.

 

[2Big2B]

But conceptually we have an inverter that has been sitting disconnected with voltage charged capacitors. Shorting out the capacitors releases a "pulse" creating a spark as the capacitors are discharged.

So why isn't it called "DISCHARGING" the capacitors ????
It doesn't make sense ...

 

[HarryN]

But conceptually we have an inverter that has been sitting disconnected with voltage charged capacitors. Shorting out the capacitors releases a "pulse" creating a spark as the capacitors are discharged.

So why isn't it called "DISCHARGING" the capacitors ????
It doesn't make sense ...

The missing part is how an actual inverter behaves.

_______________________

Suppose that you hook a setup such as :

( 12 volt AGM battery ) ---- ( breaker ) ---- ( inverter ) ---- (return back to battery neg ).

There is no need to pre-charge the inverter capacitors because the AGM battery does not have a BMS.

It will just happily power it up and away you go with getting 120 vac out of the inverter.

_____________

Now turn the inverter off and then the breaker off.

Depending on the inverter, the 12 volts in the caps will hold for 10 - 60 minutes, but much after that, it will slowly discharge down to essentially ~ 0 volts. This is due to leakage that occurs in pretty much all electronics.

If instead you start with the inverter caps charged up to 12 volts from that AGM battery and turn the inverter on, it will discharge in 10 ish seconds.

__________

So it is highly unlikely that you will be cold starting off from scratch with the inverter caps charged up in a real situation.

If the inverter caps really are charged up, then there is no need to do anything at all except turn on the breaker and feed power in from the battery.

 

[2Big2B]

The missing part is how an actual inverter behaves.

_______________________

Suppose that you hook a setup such as :

( 12 volt AGM battery ) ---- ( breaker ) ---- ( inverter ) ---- (return back to battery neg ).

There is no need to pre-charge the inverter capacitors because the AGM battery does not have a BMS.

It will just happily power it up and away you go with getting 120 vac out of the inverter.

_____________

Now turn the inverter off and then the breaker off.

Depending on the inverter, the 12 volts in the caps will hold for 10 - 60 minutes, but much after that, it will slowly discharge down to essentially ~ 0 volts. This is due to leakage that occurs in pretty much all electronics.

If instead you start with the inverter caps charged up to 12 volts from that AGM battery and turn the inverter on, it will discharge in 10 ish seconds.

__________

So it is highly unlikely that you will be cold starting off from scratch with the inverter caps charged up in a real situation.

If the inverter caps really are charged up, then there is no need to do anything at all except turn on the breaker and feed power in from the battery.

Thank you, but ...

Why don't they call it "pre-charging the inverter capacitors" when talking about using a resistor to bleed off the charge?

I guess it is what it is... Just a bit strange.

 

[HarryN]

Thank you, but ...

Why don't they call it "pre-charging the inverter capacitors" when talking about using a resistor to bleed off the charge?

I guess it is what it is... Just a bit strange.


View attachment 220796

That is exactly what it is called, "pre-charging" , short for pre-charging the inverter capacitors.

I have no idea why someone would use a resistor to bleed off the capacitor in an inverter. Just turn it on and it will bleed down all by itself due to the standby power draw. ( if the DC coming in is turned off ).

Maybe they are using it as a safety check vs owning a meter ?

Sometimes just for OCD reasons, I will take a wire and short everything out to make sure that everything is dead if I am working on someone's van power system.

 

[2Big2B]

That is exactly what it is called, "pre-charging" , short for pre-charging the inverter capacitors.

I have no idea why someone would use a resistor to bleed off the capacitor in an inverter. Just turn it on and it will bleed down all by itself due to the standby power draw. ( if the DC coming in is turned off ).

Maybe they are using it as a safety check vs owning a meter ?

Sometimes just for OCD reasons, I will take a wire and short everything out to make sure that everything is dead if I am working on someone's van power system.

Will has a video about it, and there are a number of other videos about it. When first connecting the hot lead from the battery to the inverter, expect the possibility of a large scary spark as the capacitors release energy from the voltage difference. It might even micro weld the surface of the terminals too. So, to prevent that, one can use a cement resistor to burn it off before connecting. One video suggested to use a thick artist drawing pencil in a pinch...

So, I don't see anything "charging", but instead, discharging. With the 600w or 1500w inverters I have, it isn't too serious a problem and, I guess it doesn't apply after the caps dissipate naturally... butpeople use them and, in the error of caution I just got myself one just in case.

 

[HarryN]

Will has a video about it, and there are a number of other videos about it. When first connecting the hot lead from the battery to the inverter, expect the possibility of a large scary spark as the capacitors release energy from the voltage difference. It might even micro weld the surface of the terminals too. So, to prevent that, one can use a cement resistor to burn it off before connecting. One video suggested to use a thick artist drawing pencil in a pinch...

So, I don't see anything "charging", but instead, discharging. With the 600w or 1500w inverters I have, it isn't too serious a problem and, I guess it doesn't apply after the caps dissipate naturally... butpeople use them and, in the error of caution I just got myself one just in case.

I think that I figured out the terminology question.

As you mentioned, when a live wire is connected to a load such as an inverter, there is a "discharge arc" / mini lighting bolt that spans the gap as the two get close to each other.

What you are seeing is that the power is being transferred into the inverter caps and they are "charging up" to the battery voltage.

So the resistor is "reducing the discharge arc" by allowing the flow to be moderated by the resistor.

I agree that it is ideal to "reduce this arc". I prefer to work on power systems that are not "live", so I put a breaker in there so that I can make that connection without the added fun of the spark.

One time I was working on a 270 VDC battery pack and thought that the ruler I was using to take some distance measurements was non conductive. It turned out that it had a buried metal strip in it. The resulting arc, not very far from my face was pretty exciting - fortunately the metal strip vaporized and stopped the arc, but it is something that I think about every time I am working on a battery pack.

For 12 volt systems, the arc is usually not so significant, although you can do some welding with it. At 24 volt there is a very noticeable difference in the arc strength. At 48 volt, small wires will just vaporize or even just blow off the insulation.

That is why suggest 24 volt systems for most DIY use, especially people starting out. Usually plenty of power, viable working safety levels.