Small battery bank running an inverter

[StuM]

Originally Posted by GILow

I also gave voltage ranges that were consistent with TXG's experience of running a practically identical system. So I think it is pretty clear this is an internal battery resistance/chemistry issue and all that remains is to speak to the manufacture's technical representative and get his opinion on whether treating the batteries in this way will damage them.

With the length of time that you are drawing the high Amps from a "dual purpose" battery, I wouldn't be too concerned about damaging them.

After all, it's only a couple of Ah each time and I doubt that they would experience much heating.

But as you've discovered, it will cause a fairly large temporary voltage drop. If you've got instruments running at the same time, don't be surprised if they decide to reset themselves

[TeddyDiver]

Originally Posted by GILow

.
I also stated that I ASSUMED I had a bad contact somewhere but I was able to rule it out using that very simple test.


I am starting to worry if anyone is actually reading what I posted.

I feel your pain :-( Way too common problem.

BR Teddy

[txg]

I'm still waiting for any proof or experiences from all the guys who told us that this load is too high for a 220Ah bank?

Regarding battery heating: At least with our AGM bank that's not a problem even with longer times at high loads. 60kg of mostly lead is just such a big thermal mass that it takes a very long time to heat it up. I could only once feel that our batteries heated up a little bit, and this was only about 5-10 deg. C about ambient temp. This happened when i did some tests to our alternator which meant discharging from full to 50% at 120A continuously, and then directly recharging up to 80% beginning at 90A.

[Boatwright]

The reason your inverter is tripping is the huge DC current required to operate ANY appliance that produces heat - coffee maker, hair dryer, toaster, etc. - is pulling the system voltage down to the trip voltage.

Inverters are a great convenience for operating smaller intermittent loads such as an electric drill, or a small continuous load such as a TV or stereo.

In practice no matter what the inverter rating, intermittent loads should be no greater than 500 watts, continuous loads should be limited to 100 watts. Any more than this will overload the DC system, overheat wires, shorten battery life, blow alternator diodes, etc..

We all love our coffee. There are good alternatives. We use an old-fashioned whistling tea kettle and a Melitta brand insulated drip coffee pot.

http://www.amazon.com/Melitta-Coffee...tta+coffee+pot

The coffee is great -- the only disadvantage is one of us has to get out of bed to fire up the kettle.

[Boatwright]

I should add:

The only practical way to have a 120 volt system on a yacht that will run an electric kitchen is to have a genset that produces multiple KW of AC power. If you are under sail and smaller than 40', forget the electric coffee pot.

There just isn't a DYI battery powered solution to power heat producing electric appliances for the average cruiser.

[txg]

Originally Posted by Boatwright

I should add:

The only practical way to have a 120 volt system on a yacht that will run an electric kitchen is to have a genset that produces multiple KW of AC power. If you are under sail and smaller than 40', forget the electric coffee pot.

There just isn't a DYI battery powered solution to power heat producing electric appliances for the average cruiser.

This is just plain wrong. Obviously you haven't read anything in this thread except the first post. We are doing exactly what you describe as impossible and it works fine.

[StuM]

Originally Posted by Boatwright

In practice no matter what the inverter rating, intermittent loads should be no greater than 500 watts, continuous loads should be limited to 100 watts. Any more than this will overload the DC system, overheat wires, shorten battery life, blow alternator diodes, etc..

Guess I wasted my money putting a 2.5kW inverter in then

And if more than 500 Watts will overload a DC system, I'd better remove half of my solar panels and de-rate my alternators.

Darn it, I didn't realise that my battery system couldn't be drawn down at greater than C/25 or that I need to draw continuous loads below C/100.

Thanks for letting me know.

[a64pilot]

If it's only one minute, you should be fine. I due to my advanced age think Mr Coffee or similar device when someone says electric coffee maker.
I too am a a Coffee addict, something that 20 yrs in the Army did to me.
Please understand though that your 12VDC deep cycle batteries are really in fact starting batteries, not deep cycle, but no real matter as you have them.
I still think your undercharging them, long thread so I don't remember if they are AGM or not, but if not a hydrometer is inexpensive and an easy test that will tell if they are being undercharged or not.

[rwidman]

Originally Posted by Boatwright

............ In practice no matter what the inverter rating, intermittent loads should be no greater than 500 watts, continuous loads should be limited to 100 watts. Any more than this will overload the DC system, overheat wires, shorten battery life, blow alternator diodes, etc......................

Well, that's just wrong!



You can run virtually any load with an inverter, provided the inverter and the battery system is adequate. Think of solar powered homes.

I have a 2000 watt inverter and a bank of four group 31 AGM batteries (roughly 400 AH). I routinely run a microwave oven that draws about 1400 watts and a single cup electric coffee maker (not at the same time). I get some voltage sag but it's temporary and it's no different than running the windlass or bow thruster.

The OP might solve his problem with true deep cycle batteries or he could just add one or two more batteries in parallel.

[rwidman]

Originally Posted by txg

I'm still waiting for any proof or experiences from all the guys who told us that this load is too high for a 220Ah bank? .

The fact that the inverter is sounding the low voltage alarm and the voltage at the battery terminals is dropping significantly is pretty much proof.

The voltage is dropping because there is too much internal resistance in the batteries.

Perhaps these are not true "deep cycle" batteries. Perhaps a different brand of batteries would work better. Certainly adding one or two more batteries in parallel would help.

[TeddyDiver]

Originally Posted by rwidman

The fact that the inverter is sounding the low voltage alarm and the voltage at the battery terminals is dropping significantly is pretty much proof.

The voltage is dropping because there is too much internal resistance in the batteries.

Perhaps these are not true "deep cycle" batteries.

Then it'd be starting batteries, they have smaller resistance.

[newhaul]

Originally Posted by Boatwright

The reason your inverter is tripping is the huge DC current required to operate ANY appliance that produces heat - coffee maker, hair dryer, toaster, etc. - is pulling the system voltage down to the trip voltage.

Inverters are a great convenience for operating smaller intermittent loads such as an electric drill, or a small continuous load such as a TV or stereo.

In practice no matter what the inverter rating, intermittent loads should be no greater than 500 watts, continuous loads should be limited to 100 watts. Any more than this will overload the DC system, overheat wires, shorten battery life, blow alternator diodes, etc..

We all love our coffee. There are good alternatives. We use an old-fashioned whistling tea kettle and a Melitta brand insulated drip coffee pot.

http://www.amazon.com/Melitta-Coffee...tta+coffee+pot

The coffee is great -- the only disadvantage is one of us has to get out of bed to fire up the kettle.

Just one question where did you get this information ?
I'm sure that the companies that make and sell bigger inverters (like just about all inverters. ). Would really like to know this information. I have no problems running either of my 750 watt inverters to power up to 700 watts draw. If any higher draw is needed I run both inverters in parallel. ( and yes it can be done and is actually quite easy to do)

[mitiempo]

Originally Posted by Boatwright

The reason your inverter is tripping is the huge DC current required to operate ANY appliance that produces heat - coffee maker, hair dryer, toaster, etc. - is pulling the system voltage down to the trip voltage.

Inverters are a great convenience for operating smaller intermittent loads such as an electric drill, or a small continuous load such as a TV or stereo.

In practice no matter what the inverter rating, intermittent loads should be no greater than 500 watts, continuous loads should be limited to 100 watts. Any more than this will overload the DC system, overheat wires, shorten battery life, blow alternator diodes, etc..

Totally depends on the battery bank size and the inverter size. As Newhaul posted you can parallel inverters for higher output. Some large boats parallel 4000+ watt inverters with a large battery bank. The most popular size of inverter is 2000 watts and is a good match for a battery bank of 450 AH or so, very common on cruising boats.

[mitiempo]

Originally Posted by GILow

So I think it is pretty clear this is an internal battery resistance/chemistry issue and all that remains is to speak to the manufacture's technical representative and get his opinion on whether treating the batteries in this way will damage them.


Seriously guys, I love the help, and I hate to sound ungrateful for the advice, but the whole "You are an idiot who does not know how to wire an inverter" thing is getting a bit thin.


As it is, I am probably just an idiot who did not know what to expect from batteries under this sort of load.


Matt

Nothing to do with "...an idiot who does not know how to wire an inverter." The best answers come after all the information is known though - wire gauge, distance, as well as battery size for example.

One thing we don't know is the brand of inverter. That and the low voltage cutout voltage - which should be stated in the manual - would help.

As far as inverters not being able to handle high loads when wired from smaller battery banks it is quite common. I had a customer a few years ago with 2 group 31 batteries and a 2000 watt inverter. As soon as he turned his coffee maker on the inverter shut down. Changed his battery bank to 4 golf carts for a total AH of 484 (double previous size) and no further issues.

[kmacdonald]

Originally Posted by StuM

Guess I wasted my money putting a 2.5kW inverter in then

And if more than 500 Watts will overload a DC system, I'd better remove half of my solar panels and de-rate my alternators.

Darn it, I didn't realise that my battery system couldn't be drawn down at greater than C/25 or that I need to draw continuous loads below C/100.

Thanks for letting me know.