Inversion confusion

[Dene]

I'll describe my set up and then the problem.

I have a new ProMariner 1500W inverter tied to two 6 volt golf cart batteries. The batteries were given to me by a friend. They are "workholic" and are 5 years ago, having been idle the last 3. Charging them and the starting battery is a new Pro Sport Series 12 dual charger which puts out 12 amps. This was installed two days ago and when I checked it this evening, it was indicating that full charge to all batteries. I checked the voltage of the two golf cart batteries and they indicated 13.1. There is 14 feet of cable between them and the inverter.

I'm wanting to power a 400 watt heater (only while underway) and more importantly, a Sharp 600w Half Pint Microwave. I want to power the microwave whenever I want, regardless if the engine is running....and there lies the problem. It will run about a minute before the alarm starts sounding. That's not long enough to heat my coffee water.

I suspect the problem lies with the batteries. I've check the cells with an hydrometer and they are fine. Are two golf cart batteries insufficient to run a small microwave?

-Greg

[starcrafttom]

depends on the mirowave but most likely Yes.

[rogerbum]

[thataway]

Great advice from Roger. The only thing I would add, is that you might try a pulse desulfator on the batteries (Battery minder-Pulse tech, etc) Sometimes these can bring back the somewhat sulfated plates which come from the batteries sitting.

My guess is that you will have to both put in larger wiring and get new batteries. Sams and Costco have Golf carts. One way to "check out" these batteries is to look at the weight. I found that some of the cheaper golf carts have less lead (weigh less) and thus have less capacity. For your work it may not make much difference. The other question is if the draw of the microwave is more than what you think it is? There is often a surge as the magnetron comes on line, which pulls more power. Your inverter will handle that, but the voltage will drop even more--as per Roger's explaination. (I think that he has given you adequate size wire to account for that).

[journey on]

I got my golph cart batteries from American Batteries. They had 3 grades of golph cart batteries: cheapest, middle and most expensive. Not surprisingly the price correlated with weight. So, apparently, what you were buying was more lead, which could be used to store more electrical energy (amp-hrs, in a 12 VDC system.) I, being somewhat cheap, bought the middle line. Also, being old, they were what I could slide into the aft compartment of the boat.

Now, when I buy batteries from Costco, I find that they weigh less that other batteries of the same size. So, I assume that they will have less amp-hrs. This is no statement about the quality, just the capacity.

The batteries in Journey On are ~4 years old, and I expect to have to replace them soon. They have been kept charged fairly continuously, and checked for water at somewhat regular intervals. 5 years is, to me, a long time for ordinary lead-acid batteries. But I may learn something new.

I also used 4 ga wire from the batteries to the inverter. Everything works fine, unless we forget to unplug the 1400 watt heater, when we turn on the inverter. But we get reminded.

Boris

[Fun Patrol]

First, without a way to objectively tests those old batteries, it would be a good idea to buy a new pair of Trojan T-105s. Life's too short for old batteries and old tires. Many people consider 4 years as the replacement point.

You might consider heating your coffee water on the stove? Then you could get rid of the heavy microwave, inverter and associated wiring. Maybe even a 60# battery as well. A 70 watt pocket inverter will run a laptop.

If you really need a big inverter, you should mount it as close to the batteries as possible. Really close with really big wire. Check the wiring chart and remember you have to figure a round-trip. For a full-size 1500 watt inverter the instructions will probably mention something like #0 battery cable. One axiom is to keep the inverter close to the batteries and run the longer distances with the a/c wiring.

To know exactly what your batteries are doing, install a good multi-meter, something like the E-meter. It will tell you how much juice you are using or putting in, how much you have left and more. It is a great education to see how much every item on board burns up.

Good luck with it,

Roy

[Dene]

Ok....thanks a bunch for the info. These responses are one reason why this forum is the best.

When I arrived at the boat with my new WalMart voltmeter (thanks Bob), it read 12.5 volts and indicated fully charged house batteries. The charger was on minimal charge. I verified this with an ordinary voltmeter too, on the batteries and the input to the inverter. The cables to it are 22 mm. in size. Still not sure of the gauge. They are the same size as what was originally in the inverter box, just longer.

Hydrometer revealed partially charged cells. All were the same. Incidently, the batteries are Interstate Workaholics.

I put a 400W load on the 1500w inverter and the reading plunged to 11.1, resulting in the inverter alarm going off within 30 secs. Afterwards, the installer came out and attached my original deep cycle group 27 battery to the inverter, in the same cabin compartment, a foot apart. We tested the charge and all batteries were receiving it. Then we ran the inverter with the 600W microwave and it did fine....no alarm. At this point, I intend to keep the lead battery there, attached, enclosed in a battery box. Is there any significant danger in keeping this battery within a foot of the marine inverter? Again, both are in an enclosed seat compartment.

I suspect the 14 foot cables do reduce the voltage to the inverter when it's under load. It's possible these Interstate golf cart batteries cannot be charged above 13 volts too, given their age and prior usage. (I'll look into rehabbing them as Bob described). However, with the 3rd, group-27 battery attached, I should have enough voltage to power my various applications, if it's safe and feasible with the smart charger.

-Greg