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Old 09-17-2014, 09:22 PM   #1
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12v / 120v Inverter Problem

I had installed a 1500w Canadian Tire Inverter at the time of build (I supplied) in order to run the Microwave. I have had numerous low voltage warnings and alarms when using it.
  • The wiring from the battery appears to be #4
  • The run length is the minimum possible - 4 - 5 ft approx
  • The batteries are twin 6 volt
  • The microwave is rated 1000W
  • The meter shows 12.3 V coming in
  • The trailer voltage meter shows a battery level drop (dramatic) to as low as 70% right after using the microwave. It once read 35% for a few moments

I bought another Inverter - 2500W, but before I swap it out I wondered if the twin 6 volt battery set up might be the real issue.

Any suggestions on how I solve this?

Thanks everyone!
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Old 09-17-2014, 09:51 PM   #2
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I think you are going to need #1 wire for a 1500 W inverter at that length. you would need even larger for a 2500 W inverter. With #4, you are likely getting too much voltage drop in the wire. Also, you will not get much run time on the batteries using the microwave.
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Old 09-17-2014, 10:36 PM   #3
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It could be a voltage drop problem. 4AWG wire, 5' long, 120A (gives 1500W), plug the numbers into an online voltage calculator and it shows a voltage drop of 0.2A or so. Is that enough to make your inverter complain? I wouldn't think so. The first thing I'd do is measure the voltage at both the battery and at the inverter while the microwave is running. If that's all the drop you see and your inverter still complains, then I guess you need a bigger wire. If you see a voltage drop much greater than that, then I'd start checking the various connections to see if any need tightening or improving. Also look for large nicks in the wire or anything else that might cause a significant increase in the resistance of the wire.

I wouldn't worry about the battery level monitor showing a significant drop in percentage while running the microwave and shortly thereafter -- it's really only accurate (and even then only somewhat accurate) if there's no load on the system.
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Old 09-17-2014, 11:10 PM   #4
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Since the inverter is not 100% efficient, it could be more like 150A on the input to the inverter. I assumed the 5 ft run was for both the positive and negative wire. If so, that would be a voltage drop over 10 ft of #4 (about .75 V). Add to that the voltage drop in the battery due to internal resistance and the resulting voltage could be low enough to trigger the low voltage alarm on the inverter.

I agree that measuring the voltage is a good idea. Maybe also check the owners manual to see what size wiring they call for. You can also check the temps of the wire and connectors. If there is a bad connection somewhere, it will get hot.
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Old 09-17-2014, 11:57 PM   #5
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Are others running their microwave with a 1500-watt inverter?
If so, what microwave, please.
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Old 09-18-2014, 12:00 AM   #6
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Quote:
Originally Posted by NJ Joe View Post
I think you are going to need #1 wire for a 1500 W inverter at that length. you would need even larger for a 2500 W inverter. With #4, you are likely getting too much voltage drop in the wire. Also, you will not get much run time on the batteries using the microwave.
As long as her Latte is perfect, I am good for one more day.
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Old 09-18-2014, 12:03 AM   #7
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Check the size of the jumper between the 6V batteries - it was #8 and longer than necessary on mine. I replaced it with a shorter #4.

And I do get some voltage alarms running the microwave on a 1500W inverter. It does MUCH better during the day when the solar panels are generating. This is one case where 2 dual purpose 12V batteries in parallel *might* be better than the twin 6V deep cycle (designed for lower current draw) batteries.
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Old 09-18-2014, 12:07 AM   #8
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All really helpful comments. Thank you. Everyone!
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Old 09-18-2014, 12:50 AM   #9
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I've installed a CT 1500 watt inverter but haven't needed it yet. Same conditions as yours. I'll see how it does warming up something tomorrow.

I have not doubt it'll be fine. In my previous trailer I had a 3000 watt one and it worked fine. Definitely drops the voltage but it does mostly bounce back.

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Old 09-18-2014, 12:16 PM   #10
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I have not doubt it'll be fine.
Ron
OK, I took a bullet for the team and have to eat my words:

Actually I meant because I've had previous CT inverters and they worked fine I wasn't worried about testing my new one after it was installed. Not that I knew for sure that it'd be OK with a 1500 watt load.

I don't have a transfer switch installed yet so I substituted a 1500 watt heater. Instant alarm. Switched to the 900 watt setting and ran it for 2 minutes. Starting voltage was 12.5 and ending voltage was 12.5. Average draw seemed to be about 80 amps. So I'm reasonably confident that the microwave will be OK but I'll make up a jumper and test it sooner than later.

Did ETI install your inverter? If so, I would look at how they connected the negative lead.

One thing I don't like about ETI 12 volt wiring is that they run the negative cable from the battery to the frame. Then, about a foot away, they connect the ground from the converter to the frame. To me that's very poor. My view is the negative cable should be continuous. Each terminal connected to the frame is a possible source of corrosion and high resistance.

So my question is; is your inverter negative cable continuous from the battery to the inverter?

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Old 09-18-2014, 04:52 PM   #11
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ETI installed the Inverter. The Inverter is wired direct to the battery - no frame ground.
What I DID see was the jumper wire between the 2 6V batteries is only 10/12 Gauge. That is the first thing I will change.
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Old 09-19-2014, 10:59 AM   #12
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There is another thread that i came across with a lot of good information related to inverters (sorry, i do not have the link). You may want to look for it.

There are additional considerations when trying to draw a large amount of current from flooded lead acid batteries. The internal resistance causes both a voltage drop and a reduction in amp hours. I took a look at the interstate web site ( RV 6-Volt Deep-Cycle Batteries - Buy a 6-Volt Deep-Cycle RV Battery | Interstate Batteries ) and found the following:

BCI
Group
Part Number
Ah
RC
RC
Dimensions (inches)
Warranty
20 hr
25A
75A
L
W
H
Free Months
GC2
GC2-XHD
232
475
122
10 3⁄8
7 3⁄16
11 7⁄16
12


You will see 232 Ah, with a light load of about 11.6A, over a 20 hour period . As the load increases the time you can draw that load decreases, but is is not linear. At 25A you are down to 475 minutes or 7.9 hours and at 75A it is 122 minutes. This is about 2 hours at 75A, or about 150 Ah. They do not list the reserve capacity for 150A. i will estimate it to be 1/2 or 75 Ah for the following calculations. Since you typically do not want to run your battery bank lower then 50%, this would limit you to about 37 Ah. A 1000W (output) microwave will consume 1300W - 1500W input power since it is not 100% efficient. Assuming 1400W at 120V, or 11.6A. The current needed to generate 1400W at 12 V is 116A. Assuming the inverter is 85% efficient, it would require 136A from the battery. With 37 Ah available from the battery, that would give you a run time of about 16 minutes.

Because of the internal resistance in the battery you will see both a voltage drop at the battery terminals and a reduction in Ah that can be supplied to the load. The voltage drop may be significant enough for the Alarm to sound on the inverter.

I believe the battery bank size is too small for what you are trying to do. In addition to increasing the wire size, I think you would also need to increase the size of the battery bank to (4) 6 volt batteries. Both of these enhancements would reduce the total voltage drop as seen at the inverter. Another possibility would be to switch to AGM batteries. They are considerably more expensive, but have much lower internal resistance. This means there would be a lower voltage drop in the battery and a smaller reduction in Ah under high load.

I am not an expert in this field, so I may be missing something in my analysis. When i looked at adding a microwave to my slide in truck camper, I came to the conclusion that it would not be practical to run it off of batteries.
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Old 09-19-2014, 06:18 PM   #13
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I run a 600 watt load (a drip coffee maker) for about 10 minutes on a self installed 1000 watt inverter powered by 2 Interstate 6V batteries. Actual measured amperage during the brewing is 55 - 60 amps. I can watch the current climb as the battery voltage drops. I did replace all the #10 ETI supplied wiring with #0 to the inverter as well as the battery interconnect (the recommended size according to the inverter's manufacturer). While I do see as much as a 1.5V drop during the run, after brewing the coffee it jumps back to the original voltage. The final toll is around 6 - 10 amp hours. All measurements with a TriMetric battery monitor.

If you have a #10 jumper between batteries, that needs to be replaced with the same wire size you use to feed the inverter - it carries the same current...
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Old 09-20-2014, 07:21 PM   #14
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All of a sudden my solar panels do not seem to be working very well. Only thing I can think of that is drawing on them is the radio.... But after a sunny day charge says only 44%. What gives? Last weekend was our second trip in it with electrical hookups, but I can't imagine why that would have affected it. Everything is off! Help!
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Old 09-20-2014, 07:35 PM   #15
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I was reading elsewhere that a 1200w microwave needs a 2500w inverter and one can expect alarms with a lesser inverter. I don't know what our microwaves are. Maybe ours are less.
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Old 09-20-2014, 11:11 PM   #16
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All of a sudden my solar panels do not seem to be working very well. Only thing I can think of that is drawing on them is the radio.... But after a sunny day charge says only 44%. What gives? Last weekend was our second trip in it with electrical hookups, but I can't imagine why that would have affected it. Everything is off! Help!

Does your radio have an amplifier?
If not then:
Check main power select switch position.
Check refrigerator ensure it is on AC.
Is your water heater dual ac/gas ?
Is your whole trailer powered but the inverter? I do not know if ETI powers all plugs half plug or only ones you designated.
Check heat pads if you have them are they on?
Check battery connections.
Breakers and the fuses are any popped breakers or red Leds on next to the fuses?
Check panel wiring on the roof at the panel and through the roof.
Is the panel cracked or is it obscured with dirt ?
That's all I can think of at the moment. If all is good you might have to flip a breaker off at a time for the day and see what allows the battery to charge fully and stay that way.

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Old 09-21-2014, 12:34 PM   #17
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All of a sudden my solar panels do not seem to be working very well.
Its not just you, it is everybody north of the equator (well, maybe everyone north of the Tropic of Cancer). It's called Fall ( to be followed by Winter). The sun is lower in the sky, the energy output will decrease and there is nothing anyone can do about it.

If your solar panel is adjustable, prop it up so it points directly at the sun in the middle of the day and avoid parking where the longer fall/winter shadows hit your panel.

Thinking ahead to our expected E-21 and our camping habits: I'm planning on using a second panel, at ground level, that I can move around and point at the sun, since we expect to do a lot of late fall - early winter camping.

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Old 09-21-2014, 01:20 PM   #18
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If your panels are flat on the roof you can only expect them to drop off after the summer solstice (late June).

A good RV article:

"Real World" Operating Conditions for Solar Systems used on RVs
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Old 09-21-2014, 01:49 PM   #19
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If your panels are flat on the roof you can only expect them to drop off after the summer solstice (late June).
Good point - the direction a panel faces is one big factor in the difference between ideal specs and real performance.
Even at the solstice, flat horizontal is not the most effective angle for a panel anywhere north of the tropics... but unless you want to set up some sort of folding frame and aim them every time you stop, that's what you're stuck with.

In the winter up here, a panel set vertically and facing south, such as on a south wall, would perform better than a horizontal panel.
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Old 09-21-2014, 02:14 PM   #20
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Do they make a roof mounted bracket for the solar panels that would allow them to be lifted on one side and swiveled toward the sun while camping and lock back down for travel? To me that would be ideal.
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