Battery for Marine Air CoolMate / 5000btu

[A.Vern]

Hi,

I just joined the forum after finding some great info on boat electrical systems. Here's problem.

2 weeks ago I bought a '07 Century 2400 WA and have been learning alot about the systems ( a bit challenging when the factory is no longer available to answer questions.).

Right now, my Century is sitting in my backyard slip with the Marine Air 5000 BTU cool mate keeping things nice and cool. I currently have an extension cord plugged in directly to the air conditioner.
The North Star AGM battery that is supposed to run the AC unit will charge up enough from the ProTournament 300 Quad charger to start up the system and start cooling for around 5 minutes, but then dies. This North Star is shot, as I expected prior to purchase, but I figured I'd give it a try.

So now I'm considering sucking up the 600 bucks to buy a new North Star AGM or go with two 6 volt Trojan T-105's hooked up in series.

Here's the specs on the two batteries... will the Trojan's work as well? They are a lot cheaper.
Capacity minutes at 25 amps / 75 amps / 20 HR rate Ampere Hour
North Star 400 / N/A / 210

T-105 447 / 115 / 225

Am I missing something, or does the specs for the T-105 show better ability?

Thanks....

and by the way, this boat is incredible! Too bad Century went away.

[A.Vern]

hmmmm.... does anyone has a Marine Air system they run on a battery set?

[Target9000]

Running almost any sort of air conditioning system off of battery power is a really tall order.

Look up the amp draw of the system and then compare to what your batteries can provide.

[HopCar]

There has been a lot of discussion on powering an air conditioner with batteries. The conclusion is that the AC just needs too much power to run for more than a short while on batteries. You might get away with it as long as your engines are running and cranking out the amps. You would have to do the math. Won't work long at anchor.

[David M]

You need a generator to run an air conditioning system of any decent capacity. The output of a couple outboards will never keep up.

[HopCar]

I think he might be able to run it with the outboards. He said it was a 5000 BTU unit. That should run on less than 50 amps at 12 volts, 500 to 600 watts. I wonder how much the alternators on those outboards put out?

[A.Vern]

Thanks for the replies!

From the research I've done, this system can run for 3-4 hours on the battery power alone. It's not going to go forever at sea, and is shore power capable as well.

What I'm trying to confirm before I buy a set of trojans is that the specs I've found on their website match those of the single North Star AGM.

Comparing amp hour and capacity to each other, it seems that the Trojan T-105's would be an easy and cheaper swap for the much more expensive North Star AGM.

The Marine Cool website claims a 4.3 amp draw. So in theory, with a 25 amp capacity of 400 on the NSB and 447 on the Trojan, I'd actually be better off with the Trojan... unless I'm gooning something up.

Capacity minutes at 25 amps / 75 amps / 20 HR rate Ampere Hour
North Star 400 / N/A / 210

T-105 447 / 115 / 225

Thanks again!

Aaron

[djmarchand]

Your 5000 BTU A/C will draw about 5 amps at 120V. If you power it with an inverter it will draw about 50 amps DC. Those two Trojan T105s have about 150 AH of capacity at that discharge rate. So they will be stone cold flat after 3 hours.

You will need at least four pairs of T-105s to power that A/C overnight. And how do you recharge them with a low amp outboard alternator?

[GordMay]

Originally Posted by djmarchand

Your 5000 BTU A/C will draw about 5 amps at 120V. If you power it with an inverter it will draw about 50 amps DC...

Originally Posted by A.Vern

... The Marine Cool website claims a 4.3 amp draw...

The AC specs certainly refer to AC current draw.
As noted, 12V operation will draw at least 10 times the current of 120V operation, PLUS various inefficiencies, that could add another 15-25%.
Accordingly, battery operation is not feasible.
The Trojan batteries represent better value than the North Star AGMs.

[DeepFrz]

People have installed huge battery banks on larger long range cruisers (such as 1600 ah @ 24 v) in order to run AC overnight without a generator. Invariably they find it just doesn't work and they end up running the generator and find they have a very expensive battery ballast system that needs replacing way to soon. I have often seen these boats listed for sale and they sit on the market for a long time.

[denverd0n]

No, you're not "gooning" anything up. (Never heard that term before.)

You are, however, missing a couple of things, I think. First off, as Gord pointed out, there are going to be inherent inefficiencies in running the thing off of battery power through an inverter. Subtract 10% to 15% from your time estimates.

Then the big one. These capacity figures that the battery manufacturers publish are always assuming that you run the battery flat dead. Draw every last possible amp from it. Do that on a regular basis and your batteries are not going to last very long at all. Perhaps more important, your inverter and A/C will probably quit functioning because the voltage has dropped too low long before you get every last amp out of the battery.

For the batteries to have any kind of a reasonable lifetime (and maintain useful voltage) you need to plan on never drawing more than about 75% of their capacity out of them. 50% or 60% is even better. That cuts your operating minutes WAAAAY down!

If you can run that A/C for 2 hours on your battery bank you will be doing darned well. Even at that, though, you will be shortening the life of your batteries pretty seriously.

[HopCar]

I think what you're missing here is that the AC draws only 5 amps of 110 volt power (550 watts) but it will take about 50 amps of 12 volt power.

Since you can't draw all of the available power out of your batteries without damaging them, divide the published capacity by two to get the usable power.

There probably isn't room to install a real marine generator on your boat. If you want AC while you anchor over night, a lot of people use portable Honda generators. There are dangers involved in this approach and it has been discussed to death on this forum. Non the less, a lot of people, my self included, do it.

[A.Vern]

Originally Posted by HopCar

I think what you're missing here is that the AC draws only 5 amps of 110 volt power (550 watts) but it will take about 50 amps of 12 volt power.

Thanks, this is the part of the puzzle I've been missing. I've seen the Marine Air listed as taking 5 amps and 50 amps... but now I understand it's a difference of AC and DC power supply. The generator idea has me thinking...

Proline ran a similar setup to Century using three AGM batteries. It may not make it all night, but for that I would expect to be hooked up to shore power. If I can get the battery setup to work for a few hours on the water so the wife and kiddos have a cool place to escape the heat... it may be worth it.

By the way, shore wise, I love this Cool Mate system. I've been running it 24/7 set at 80 to keep the cabin dry and the mold down, and last night had it at 72F so the kids could sleep in there overnight.

Thanks again all for the help, I'll post how it ends up.

Cheers,

Aaron

[A.Vern]

So here's the latest....

Marine Air recommends 3 batteries hooked in parallel vice one large battery. I've got room for 3 batteries, but the dilemma now is how to charge 3 batteries off a single charger outlet (4 outlets total from the charger, but first 3 already go to the port, starboard and house batteries).

[Chipg]

I don't think your going to be happy until you add a small portable honda generator to your setup.