Inverter - Is This Normal?

Bill Roosa · Feb 28, 2016

yes totally normal. 1400 watts is 1400/12.5=112 amps. that is about the load of a starter motor. Imagine cranking your engine for 30 seconds straight. Don't know too many folks that would consider that as not HEAVLY loading the batteries. 12.5 volts is pretty good BTW.

Benny17441 · Feb 28, 2016

A battery voltage reading is a moving target. A battery that has been subjected to a load will give a lower voltage reading while one that has been subjected to a charge will give a higher one. When the battery does not have enough capacity left or the rate of discharge is too high most inverters will cutoff and beep an alarm. A high rate of discharge reduces significantly the ability of a battery to put out rated capacity. You likely got a lower voltage reading than actual but that is a very high load to run through an inverter even with a nice size bank like you got.

seadaddler · Feb 28, 2016

I have found out any time I use the microwave,electric coffee maker or hair dryer
or any high draw off the inverter I watch my battery monitor voltage go down real fast.
I did use the electric coffee maker first thing every morning after being anchored over
night.
I felt I was really killing my batteries and so now here it is 5 years with my 4-6 volt
T-105's still doing real good.
I now have solar panels and don't use my FP Gen as much and not to use it in a anchorage early morning or very late at night,but my wife and I like a hot shower,I do make coffee early morning using the inverter and wait to make hot water with Gen.
I just make sure not to lower the batteries lower than 50% and use the inverter lightly when it comes to high draw appliances.
Nick

centerline · Feb 28, 2016

Bill and Benny are both right...
the batteries are being discharged at a rate of 112amps per hour, but not a total of 112amps in the 30seconds you are running the heat gun...
the discharge rate will likely be higher than the numbers that Bill gave, and depending on how efficient the inverter is, it could be a considerable amount more.

but what you are seeing on your gauge is what Benny describes... its a heavy load and it will show as such, but if you use the heat gun for a few minutes, it may even quickly draw down a bit more before the drop in the gauge reading slows down....
and if you use the heat gun for 3-4 minutes, the gauge reading may get down to 12.1, but after putting the heat gun away the gauge voltage will slowly climb back up, and show what you actually have left in the bank.....
a volt gauge is not a good tool to use when attempting to see how many amps we are using from the battery, its only a crude indicator. there are much better (and more costly) devices to measure what is taken out of and put back into the banks.

inverters, as handy as they are sometimes, they are NOT an efficient means to get the job done.

capta · Feb 28, 2016

I recently installed a Blue Seas Systems M2 1834 DC multimeter and it shows exactly what my net amperage into or out of the batteries is at any moment. With 20+ amps of potential solar and a windgen, it's very interesting to watch this meter when the vacuum, microwave or toaster oven are munching the amps.
Big boy toys sure are fun.

cygnussailor · Feb 29, 2016

Assuming 100% efficiency the current draw on the batteries would be about 116 amps. Allowing for a 90% efficiency rating on the inverter, the actual current draw would be about 130 amps. I get very similar results to yours when running my 900 watt microwave for a minute or so. Sounds normal to me!

cygnussailor · Feb 29, 2016

But yeah, I mainly got it for the coffee maker. It's a PITA to heat water in a pan and pour it over grounds.[/QUOTE]

You have got to be one dedicated coffee drinker!!!

Stu Jackson · Feb 29, 2016

cygnussailor said:
It's a PITA to heat water in a pan and pour it over grounds.

A pan?!? That's why they invented tea kettles.

Stu Jackson · Feb 29, 2016

I'm surprised no one has yet mentioned the Peukert Factor.

Beneteau 321 · Feb 29, 2016

A bit off topic but having a good coffee in the moring can make your day ,we use a Coleman Camping coffee maker from Canadian tire
Looks like a electric coffee maker except it sits over a burner on our propane stove doesn't take long for a fresh brew

Head Sail · Feb 29, 2016

Stu Jackson said:
I'm surprised no one has yet mentioned the Peukert Factor.

Very true when I used to drink coffee, we would usually Peukert first.

Maine Sail · Feb 29, 2016

GorillaToast said:
i just installed a Xantrex 2000w PSW inverter.

The problem is if I use, for instance, a 1400w heat gun, within 30 sec it has brought the house bank down to 12.5v.

Your batteries sound pretty healthy considering you are hitting them with a 123A - 129A load, depending upon inverter efficiency.....

centerline · Feb 29, 2016

Stu Jackson said:
I'm surprised no one has yet mentioned the Peukert Factor.

+1 for the tea kettle..

can the peukert factor be figured in when using an inverter?.... I know it has an influence on the storage capacity of the banks, (and so, the usable amount that is available for the inverter to burn), but other than that, on the downstream side of the inverter I dont think it has any effect... maybe someone can educate us more on this.

Maine Sail · Mar 1, 2016

centerline said:
+1 for the tea kettle..

can the peukert factor be figured in when using an inverter?.... I know it has an influence on the storage capacity of the banks, (and so, the usable amount that is available for the inverter to burn), but other than that, on the downstream side of the inverter I dont think it has any effect... maybe someone can educate us more on this.

An inverter is a constant power device so the output will remain steady, lets call it 1400W. So long as the input voltage is above the inverters low voltage cut-off the inverter will output 1400W. The problem with a constant power device is that as battery voltage drops the necessary current to maintain the output increases. Below calcs are using an inverter efficiency of 85%. As voltage drops on the DC side inverter efficiency can also change..

1400W / 12.8V = 109.4A X 1.15 = 126A

1400W / 11.3V = 124A X 1.15 = 143A

A 400Ah battery bank is only a 400Ah bank with a 20A load at 77F (when new, just broken in, and absolutely healthy)

A 400Ah bank with a Peukert of 1.3 becomes a 222Ah bank at a 143A load.

Gunni · Mar 1, 2016

Which is why I pulled my inverter and gave it away.

Bill Roosa · Mar 1, 2016

Coleman makes a dandy stove top coffee maker. Yes it takes longer than an electric but my propane tank holds quite a few more pots of coffee than my battery bank does. Average time to brew is around 30 minutes. That would be 1 sail-time time period or a single bell in ships time.
When testing your microwave be sure to actually time the timer on it. i know mine runs at double time so 1 minute on the oven is really only 30 seconds of microwaving. Something to do with modified sinewave (vs true sine wave) Alternating current and those little black plastic boxes on the circuit board not liking it much.