sheriffav8r

I've got my truck battery/inverter system set up and it seems to run fine until I try and run my portable AC off the inverter. My setup is 4-255AH 6V GC batteries wired in series/parallel, 2 gauge wire and clamp on lugs, and a 2500W inverter. It's an AC Delco inverter I bought from BJ's but seems to work fine. I'm guessing it's a MSW and not a pure sine wave (duh, it's cheap). The inverter never hiccups or shuts down from the Air Conditioning power draw. There's an electronic DC battery isolator that separates the vehicle batteries from the GCs. Here's my setup: 2 6V batteries wired in series and then wired in parallel for 2 12V banks of 225AH batteries. Positive inverter wire is picked off one bank and negative off the other bank for equalization. The negative is also grounded to the truck. The positive has a wire to the vehicle battery isolator.





Battery banks sit on opposite sides of the truck bed and the connecting cables are equal length at 6'. Wire run to the inverter is about 6', too. The cables never get warm and current draw is equal across all batteries and banks.

I power up the inverter and the air conditioner. The inverter pulls about 80 Amps DC and the AC pulls about 8-9 Amps AC while putting out 114VAC. The batteries start at about 12.5VDC for each pair and the pairs are equal. After a few minutes the DC amperage starts climbing and the AC voltage starts dropping. The DC amps peak at 150ish and the voltage drops to 105VAC and the AC compressor kicks off the line. While my DC battery voltage is steadily declining, it never falls below 11.6-11.8VDC and jumps back up to 12.4 when the AC kicks off. The AC unit will pull 8-9 amps AC all day long on shore power and the voltage is steady at 113-114VAC. Is this just a poor inverter? What's happening?

bigdave

Yes, I would say that it is a poor inverter or that it is not rated correctly and isn't big enough for what you are doing. How big of AC is it?

carl48

i also think it is the inverter. you did a very good job of the wiring. the ac is drawing about 1kw i would go with a 3,500 watt true sine wave inverter. another thing you need to do if you are plugging the trailer plug in to the inverter for power to the ac you must unplug the trailer inverter. on the new trailer inverters you will damage them with a modified sine wave inverter and on a true sine wave it will try to charge the batteries

slowflyer2112

You need to think in watts, As the voltage drops, the amps will go up.

V times A = watts

What is the total watts available over time and what is the total watt draw.

As the battery voltage drops due to heavy current draw, the current draw will increase and the same is true on the opposite side. As the inverter try's to maintain voltage for your equipment. As the battery voltage the inverter efficiency will drop.

sheriffav8r

The AC unit is a portable 9000BTU job. Like I said, it only pulls 9 amps AC so that's about 1kW give or take. It's a 2500W inverter that doesn't even hiccup when the AC is running. The inverter is thinking it is performing correctly and never kicks off. I'm trying to find out why the amps steadily ramp up from 80 to 150, the AC voltage steadily drops from 114 to 105 where the compressor kicks off. I'm pretty sure the compressor is kicking off due to low voltage, but why is my amperage climbing (almost doubling) over a period of 5-6 minutes? The battery bank starts out at about 12.5V and gets no lower than about 12.0V before the first compressor kick off. This inverter should be producing 110VAC down to 10.5VDC on the bank. I know about watts, volts, and amps, but am just trying to figure out if it is the MSW inverter for sure or if I have messed something up somewhere else. The way I figure it I should have 2-3 hours at 80 amps/12VDC to bring my 225AH battery bank down to 50%. I'd be happy with even half that, but I kinda wanted the A/C to be working properly along the way.... As for the camper inverter, it is just a cheap WFCO converter. 110VAC pass through with breakers and 12VDC battery charging. Will the MSW inverter mess that up or not?....

Jeff in TD

IMHO you likely need a much larger bank of batteries to supply 80 amps for more than momentary use. Amp hours on a deep cycle are generally rated on a 20 hour discharge. Drain them faster than that, and you get much lower output. As battery voltage drops you would typically see amps go up, as the inverter is producing the same watts and the battery voltage droops in a few minutes with a large load.

Also, motors typically don't react well to modified sine inverters.

Anyway, if you want to run AC, I'd highly suggest an Onan built in, or a Honda EU3000 or a pair of EU2000's.

Foxborough

I ran into the same thing with my boat lift a few years back. I needed 13 amps, 120v for approximately 2 minutes to run the lift. The two sites I used was these http://www.windsun.com/Batteries/Battery_FAQ.htm http://www.phrannie.org/phredex.html . In a nutshell the amp hours of a battery are what a battery can produce with a slow drain. When you draw larger amps the batteries need to be derated to around 50% of the posted amp hours. I also remember when the batteries get to 12v they are about 50% done. I put (2) batteries on my boat and planned on using one for the inverter and one for the engine. I mounted a battery switch so I could select either battery or use all for the engine or inverter. I did all the math and cables but could not figure out why the one battery couldn't do the job like I had planned. That was where I learned about batteries under high drain conditions. Also the deeper you drain the batteries and recharge the quicker they "wear out". You should plan on only using the batteries to the 50% range (12v) then recharge. Batteries charge and discharge at different rates as they age so batteries should be the same age also. That is all I can think of for now. Just research thru the (2) sites and do the math it's interesting (at least to me ).

FiverBob

I have a sneaking idea Jeff is right on the money. Anything other than a sine wave will cause motors and other things to overheat. That compressor is probably getting hot and pulling more current until it finally shuts itself off. Even though I can fun my microwave off my sine wave inverter, I always kick on the genny if my usage will exceed 3 or 4 minutes. It pulls soooo much current from the batteries it just isn't worth it. I then leave it on a while to recharge batteries.

Bob

sheriffav8r

After further review, here are some findings and more questions:

I ran the A/C off house power: 120VAC, 7.6-7.8Amps with no wavering whatsoever.

I ran the A/C off my Yamaha YG2600 generator: 124VAC, 7.7Amps same as above.

I ran a 1500W ceramic heater/fan directly off the inverter: 124VAC, set at 9.5A AC, saw about 95A DC. Ran for about 15-20 minutes with no wavering, steady battery draw. Started battery bank at 12.5 and went to 12.2VDC during the test and pretty much stayed there.

I ran the A/C directly off the inverter: 124VAC, 7Amps AC, 75Amps DC, same battery draw as above. I ran it for about 10 minutes and the voltage started to go down, but no lower than 120VAC. DC amp draw very slowly climbed to 95A and the AC draw climbed to about 10.5 amps. I started the truck and the voltage held steady at 12.4VDC with an amp draw of 95 amps. The amps continued to climb and the compressor kicked off. While I didn't see 150ADC this time the amps unmistakeably kept climbing. Again, the inverter never even hiccuped and showed green lights the whole time.

Conclusions (for me at least):

1. My A/C motor does not like MSW inverters. Question is, what does my Yamaha generator have and why does it work fine with the A/C?

2. My battery bank should be able to hold an 80A draw for a couple of hours. While some may disagree, my heater experiment showed me that the batteries held up just fine. I'll do a longer test in the near future to see how long they last to 50% at 80A draw.

3. I need to find a pure sine wave inverter. Anyone have a Sunforce 2500W? They have them at Sams, Costco, NorthernTool, Camping World....