Adding additional outlets

Riwright · 01-20-2012, 03:12 AM

I am adding an auxiliary battery that will be used to power a CPAP machine. This battery will have it's own converter and will connect to a dedicated 12 volt outlet. This way I can use the main house batteries without having to worry about running out of power for the CPAP. I plan to locate the aux battery in the rear battery compartment of my 3124KS (I already have one of the house batteries in there.)

I need to get AC power back there to run the aux converter. Any ideas on where to pick up the AC to bring it back? I have a plug by the wardrobe and I might could tap into. I could also grab juice coming out of the back of the distribution panel.

Does the Trailmanor use garden variety household wire? It looks pretty standard to me.

scrubjaysnest · 01-20-2012, 04:50 AM

Quote:

Originally Posted by Riwright

I am adding an auxiliary battery that will be used to power a CPAP machine. This battery will have it's own converter and will connect to a dedicated 12 volt outlet. This way I can use the main house batteries without having to worry about running out of power for the CPAP. I plan to locate the aux battery in the rear battery compartment of my 3124KS (I already have one of the house batteries in there.)

I need to get AC power back there to run the aux converter. Any ideas on where to pick up the AC to bring it back? I have a plug by the wardrobe and I might could tap into. I could also grab juice coming out of the back of the distribution panel.

Does the Trailmanor use garden variety household wire? It looks pretty standard to me.

I don't know where your TM converter/distribution panel is at, but if in the back like 2720SL's that maybe the easiest place to pick up ac power.
The AC wiring is standard house wiring.
For the 12 volt wiring use #10 AWG, it can be either solid or stranded but stranded is eaiser to work with. I prefer marine grade tinned wire for DC circuits.

ELM-JLM · 01-20-2012, 09:00 AM

Take off the outside refer vents and you'll find a multitude of AC wiring. Much of it on my 2619 is marked!
Very easy to work with while standing!

**Bill** · 01-20-2012, 11:01 AM

Your plan for a separate CPAP battery is good, but your plan for keeping it charged may be more ambitious than it needs to be. An easier (and much cheaper!) approach would be to let the TM's onboard converter keep the CPAP battery charged, and use a battery isolator, just like the one found in your car, to keep the TM from draining the CPAP battery. In your car, the isolator prevents the TM from draining the car battery. You would use a similar isolator to prevent the TM from draining the CPAP battery. Now your cost of a charge circuit is about $10, and it is a lot easier to install than a full-blown charger.

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If you are really bent on a separate charging system for the CPAP battery, you can mount the aux converter anywhere that AC power is handy, and then run the converter's 12-volt output to the battery. They don't have to be located in the same spot. Although you can certainly use wire as heavy as #10, I'm not sure I see the need. Be sure to put a fuse at the battery end of the run, of course.

And you don't need a full-blown converter for this application. What you are looking for is a battery charger. Get a decent one. A three-stage charger is good and they are inexpensive, but I recommend against the super-cheap trickle charger or "battery maintainer" or Battery Tenda sorts of things. Good but inexpensive battery chargers can be found by looking at sites designed for fishermen, who use them to charge the battery for their trolling motors. These folks want their batteries to be fully charged at a moment's notice, but not overcharged even after weeks of non-use. Guest Industries used to be a premier supplier, but I think they were bought out by Marinco, so check there for details.

And there is no need for a high-power charger, such as those used for charging the trailer's house batteries. A good value of charge current might be three times the current drain of the CPAP machine. In other words, if your CPAP draws 2 amps, a 5-amp charger would be in the right ball park, and a 10-amp charger would be more than enough. Expect to pay about $75 for a very good one. You can usually find them for less money on eBay - for example, there is currently a Marinco (Guest) 2608A 6-amp charger on ebay for $59 with free shipping.

Bill

01-20-2012, 03:45 PM

The 3 stage charger that I bought a few years ago was just under $100. It has a 40 rating:

Black & Decker VEC1093DBD Smart Battery 40/20/10/4 Amp Battery Charger

Since you do not need 40 amps, then I certainly see no reason for you to spend more than $100.

I have a 3 stage charger on my ATV:

Battery Tender 021-0128 Battery Tender Plus 12V Battery Charger

It has 1.2 amps. Cost is $44 at Amazon. Very small unit.

Riwright · 01-20-2012, 06:43 PM

Thanks for the responses. Good data.

The CPAP draws a lot of juice. An average nights's run can take 25AH. A really cold night it can draw 33AH. Peak amp draw is around 7A. (I have a Watt's Up meter that I hook to it so I know a lot about what it draws.) I plan to use a battery that is at least 100AH to power it. We lose power a lot where I live and I use a 100AH battery at home, it works very well.

I had considered the battery isolator but there are a couple of things that seem less than ideal to me. With the diode type there is a voltage drop and the batteries would be less than fully charged. The relay type avoids that but I am concerned about the fact that the two battery banks would be at different states of discharge when I hooked up the generator. Since the charger would see the average of current across both banks then one bank would get too much current while the other one would not get enough. Two converters would give each battery exactly the juice that it needed. I am not sure how important this is. I assume that when you boondock that you need to charge the batteries fully and do it quickly so you can turn the generator off. I think a system that dumps juice into the batteries quickly would be best.

It does complicate the wiring though and it costs more. With a single converter I could just put the second battery in place and hook it up right in that back storage bin. Definitely easier.

**ShrimpBurrito** · 01-20-2012, 08:44 PM

Very well thought out. I think the unequal rate of discharge (and thus recharging as well) is a valid concern. Given a charger is only maybe ~$50 more than a relay, that seems like the way to go.

Since that the aux battery is already going to be in the rear compartment, I personally would install the new charger/converter back there as well, and connect it to the AC supply behind the converter. I think I would actually probably just wire in a standard GFI outlet in the rear compartment to do this.

Alternatively, you could just hook the aux battery in parallel with the house battery and see how you do over a weekend. Of course, long term, you'd ideally want all the batteries in parallel to be the same age and size. We occasionally have company camp with us that uses a CPAP, and we've camped 2 consecutive nights with it running (on at least 2 different trips) with a comparable draw as yours. We have LED lights, and don't have any other major draws outside of the normal TM appliances....no hair dryers, toasters, TVs, etc. And with our Trojan T-105s, we had plenty of power left. Easily could have done 1 or 2 more nights. They are rated for 225 Ah, and I figure I can regularly use ~60% of that, or about 135 Ah.

If you're already planning on using a generator and a newer high charge rate converter, you'd only have to get through one night before having the opportunity to recharge. You'd have to have some other serious power demands to not make it that far, or most likely, even much longer.

Dave

**Bill** · 01-20-2012, 09:34 PM

Quote:

Originally Posted by ShrimpBurrito

I think the unequal rate of discharge (and thus recharging as well) is a valid concern.

Dave -

I'm not sure why it would be a concern. After all, if you boondock for a night or two on battery-only, then start the car in the morning, the alternator in the car sees the car battery (presumably still well charged) and the trailer battery (considerably discharged), and no one gets upset about that. With a good charging system, the weaker battery simply hogs the charge current until its state of charge comes up to something approximating the stronger battery.

Maybe I'm missing something ...

Bill

Barb&Tim · 01-20-2012, 10:20 PM

Quote:

Originally Posted by Bill

Dave -

I'm not sure why it would be a concern. After all, if you boondock for a night or two on battery-only, then start the car in the morning, the alternator in the car sees the car battery (presumably still well charged) and the trailer battery (considerably discharged), and no one gets upset about that. With a good charging system, the weaker battery simply hogs the charge current until its state of charge comes up to something approximating the stronger battery.

Maybe I'm missing something ...

Bill

I second Bill's thought on this. I see no reason not to use the existing converter with an isolation relay to charge both batteries.

Tim

**ShrimpBurrito** · 01-20-2012, 11:10 PM

I've got charging concepts of series and parallel mixed up.

Bill, I agree with your original assessment.

Along those same lines, taking the one-converter approach, one thing to recognize is that since the discharge rates will be different, one of the batteries won't be charging initially (as Bill describes). So, for example, if one is at 80% and the other at 40%, you won't be able to top off the 80% one for some time, depending on the charge current. Dual chargers would fix that.

Also, one thing you'd want to consider is the charge output of the converter in the TM. You don't say what model TM you have, but if it's an older model, the max charge output in those converters (like mine) is about 6 amps. You would be running your genny a long time to charge 2 batteries with so little current.

Dave