Interesting real world load test

[MikeRuth]

Today I installed a new 1500 MSW inverter. 

As some of you know I'm building out a Ford E-150 and I have installed two T-105's and followed along the voltage drop calculators etc. 

It looks as though I need to increase my supply wiring from my test Even though I'm one size larger than whats called out. 
I'm running 6 feet of THHN #2 wire to a buss bar and then direct to the inverter just 10 inches from the Buss. All #2 wire. 

so today with fully charged batteries I put it to the test, first off was a 675 watt load that was showing about 62 amps into the inverter. The volatage at the buss bar dropped to 11.8, not to bad. Cranked it up to 1275 Watts and the voltage dropped to 11.2. that test was only for 5 minutes. 

Then without a recharge I fired up the Shop Vac. 6.5 Horsepower that tests out at 975 Watts and ran that for about 15 minutes. No problem but I was down to 10.8 under load

Checked all of the wiring and connections for hot spots, nadda, all looks good. 

So I'm pretty happy but I think I might do better with #0 supply instead of #2. Thoughts? 

lastly I do have a Continuous duty Solenoid between the battery and the alternator. The tests above were done with that connection open. 
So I next fired up the Van and set my idle to about 1500 rpm and closed the switch, initial  inrush to the battery was about 75 Amps and then started to taper off rapidly down to about 40 amps. steady for a few minutes.  Again this seemed good. As a quick test while the van was running I flipped on the Shop vac and checked the draw, 90 amps to the house, and still had about 24 to the starting battery. again not bad. BUT the continuous duty solenoid terminals started to heat up more than I like. In fact the entire unit got hotter than I liked. 
I only ran the vac for a minute or so and then turned it off, took another check and the current had dropped back down to 40 amps. At that point I shut it all down. 

I'm a little perplexed as to why the CD solenoid got so damn hot. Wondering if this unit is not really rated at 150 amps! That's it spec and short burst rated to 300. 
Any ideas>? 

Mike 

 

[jimindenver]

I did a search and got this

My continuous duty solenoid gets hot. Is something wrong?

The coil circuit (control circuit) in a continuous duty solenoid is usually energized for long periods of time. Under these conditions the coil will generate heat and within less than an hour the solenoid housing will become hot to the touch. This is normal. Always make sure that all wiring is properly sized for the load it is carrying, that the terminals are the correct size and have been securely crimped to the wire, that the terminals have the proper torque to the solenoid studs.

Alternatively, you might be able to use the Latching Solenoid that only needs a one-time momentary actuation to stay in the On position.

 

[akrvbob]

On a 1500 watt inverter I would use nothing less than 2/0. Ought might work but I'd play it safe, especially at 6 feet.
Bob

 

[SternWake]

Did the inverter wires/ terminals get hot?


The CTS could be a latching solenoid too. I once wired up a latching solenoid as a regular one and it got super hot.  I did not know it was a latching one and deemed the solenoid a POS.  It might not have been a latching and was a POS, but I was unaware at the time of latching solenoids.

Those t105's, all GC batteries are not known for holding high voltages under heavy loads.  I think they did pretty good considering.  GC batteries are built around maximum cycle life.  A pair of new 12v starting batteries in parallel would beat t105's voltage wise, under the same loading, but of course they would not have much cycle life in such an application.

Try testing voltage at the inverter terminals to see how much your 2awg is losing over that 6 foot/12 foot run.

You can run another fused cable from alternator(+) to the engine battery side of the Solenoid, if you are taking power from the starter battery.  This allows most of the current to bypass the too thin stock alternator charging circuit.

Looks like your alternator is pretty capable at Idle speeds.  Mine is not.  Soon I will thermal epoxy a thermistor to my alternator casing to see just how hot it gets when maxed out.

 

[IGBT]

Remember, 6 feet means 12 feet round trip for current.

2 AWG wire has a resistance of 0.1594 ohms per 1000 feet

Your 12 foot round trip has a resistance of 0.00191 ohms, but call it 0.002 ohms since you have additional short run.

100 amps though 0.002 ohms will produce a 0.2 volt drop.

It isn't really that bad.   Under 100 amp load the batteries themselves are going to drop down to 12.1V or so because of internal resistance if they are fully charged.   If they were at 50% then under load they will drop to around 11.8V.  Add in the voltage drop in the wiring and you are at around 11.9V to 11.6V at the inverter with a 100 amp load.

Your voltages do seem a bit low, but unless you are wrong about the wire length I do not think all of the drop is coming from the 2AWG wire.

It is interesting the shop vac was only drawing 975 watts.  My Magnum 4kW 24V input inverter was taking 63 amps with a 100 amp surge to power a similar 6hp shop vac.  (1500 watts battery power input to the inverter, 2400 watt surge)

 

[IGBT]

Remember, 6 feet means 12 feet round trip for current.

2 AWG wire has a resistance of 0.1594 ohms per 1000 feet

Your 12 foot round trip has a resistance of 0.00191 ohms, but call it 0.002 ohms since you have additional short run.

100 amps though 0.002 ohms will produce a 0.2 volt drop.

It isn't really that bad.   Under 100 amp load the batteries themselves are going to drop down to 12.1V or so because of internal resistance if they are fully charged.   If they were at 50% then under load they will drop to around 11.8V.  Add in the voltage drop in the wiring and you are at around 11.9V to 11.6V at the inverter with a 100 amp load.

Your voltages do seem a bit low, but unless you are wrong about the wire length I do not think all of the drop is coming from the 2AWG wire.

It is interesting the shop vac was only drawing 975 watts.  My Magnum 4kW 24V input inverter was taking 63 amps with a 100 amp surge to power a similar 6hp shop vac.  (1500 watts battery power input to the inverter, 2400 watt surge)

 

[ccbreder]

i think you need two more GC batteries.

 

[MikeRuth]

I would love two more GC batteries but have no where to put them .
Thanks for the comments guys,

I relied on the Blue Sea systems VDC and the results for 6 feet 125 amp dynamic load were #4 or #2. I went back this morning and double checked and entered in 12 feet for a complete round trip wiring. Actually I'm sure I indicated the length correctly back when I originally did the Calc. Again that VDC says#2. I know that's not the gospel

Bob thanks for that suggestion, amazing how much larger that is than calculated.

SW no, nothing got hot Except the solenoid terminals when I did the load test with the vac running and the engine fired up, and My connection is direct to the alternator. the terminals warmed first then the body. I don't plan on having the engine running normally but wanted to see how it worked out.
the voltage I had measured was at the inverter terminal. I was comparing to the standing no load voltage at the inverter. I didn't want to take the time to try and get a DVM connected directly to the battery terminals yesterday as the batteries are tucked up under the side of the van, not an easy place to get to. Since I do have everything in place this weekend I'll drop the batteries and rerun the test with a DVM on the battery terminals and one on the inverter terminals for a dead on comparison.

As mentioned I'll do a couple more tests. One will be to remove the 150Amp CB at the terminal, I'm really curious if it has any affect on the VD.
the other will be to eliminate the CD solenoid, just bolt the two wire ends together and then check for terminal heat. I'm confident my terminal ends are excellent but won't hurt to test.

After that I'll evaluate replacing that #2 wire. I'm not opposed to doing that but then again, I also need to evaluate just how often and for how long would I ever put that kind of strain on the system. My gut says not very often, but I do want it safe and sound.
As always thanks for your input guys. I'll post up the results as soon as I have them.