Battery Charging Through DC Socket

[grill-n-go]

When a TM is not in use, in storage. Does anyone know if its possible to keep the TM battery charged with one of those solar trickle chargers that plug into a car's lighter socket? The idea is to plug it into the DC socket by the refrigerator. The link provides an example of these trickle chargers.
http://shop.store.yahoo.com/safetyce...batsolcha.html
I know there is also the issue of getting a wire thats long enough...

[Bill]

The concept is good. This particular solar charger may not be big enough.

The problem is that the trailer electrical system may have some "parasitic" loads. These are items that take a small but continuous current from the battery. Examples include the LP leak detector (but TM has made sure that this one is disconnected when the bathroom wall is folded), and the radio pushbutton memory if you installed a radio. I'm not sure if the electronic controllers for the furnace and the water heater consume standby current, but they may be parasitic loads as well.

The only way to know if you have parasitic loads is to close the camper, and use a meter to measure battery current. Most any inexpensive digital voltmeter (DVM) will do the job nicely.

If there are ANY parasitic loads, the problem is this. The parasitic loads consume power 24 hours a day. But the solar panel generates power for only about 4 hours per day (give or take a little, depending on where you live). So the solar panel must be able to generate 6 times as much power as the load consumes, just to break even.

To further complicate matters, solar panels generate power only when they are in BRIGHT sun. If the panel is in the shade (tree, house, carport, etc), or if the day is overcast, or if a cloud passes in front of the sun, the panel's output drops to near zero. And the panel must be aimed directly into the sun, which means it must be aimed due south, and tilted up by about 45 degrees.

The link in your post doesn't tell us how much power is produced by the panel you are considering. However, based on the picture, it looks like the active area is no more than 4" x 12". Since solar panels produce about 11 watts per square foot in bright sun, this panel produces no more than 4 watts of power, or about 300 mA of current.

In my TM, the radio's pushbutton memory consumes about 275 mA, and as mentioned, it does so for 24 hours a day. So the panel you are looking at, operating only 4 hours per day, would be significantly too small to support the radio's memory - let alone any other parasitic loads.

The radio's memory is probably the worst parasitic load. If I recall correctly, Mike Laupp rejiggered the power connection on his radio to eliminate this load, but as I mentioned, there may be others. I can give you a lot more info on solar panels - much more than you want, I'm sure - but none of it answers your question until you know how much of a parasitic load your TM has. If you can wait a couple weeks, I will measure mine, but it is not guaranteed to be the same as yours. Sorry it isn't simpler.

How long at a time will your TM be in storage, without access to AC power?

Bill

[Caver]

I doubt if the automotive style solar charger would put out more than 2.5 watts in full sun. In the winter with the sun at low angles and with a limited number of hours, it might not overcome the "phantom loads" on the TM. Mine is pretty high at over 0.1 amps. The 0.1 amps work out to 2.4 amp-hours/day. In the winter the solar charger might achieve 1 amp-hour/day if placed in full sun for most of the day. At these low currents the size of the wire is not a factor.

The size of solar panel you need is going to vary a lot with where you are located and how it's mounted. The normal recommendation is to remove the batteries and store them charged in a warm location.

Several of us belong to this solar forum. It has a wealth of information on using solar power.

http://www.wind-sun.com/forum/

This is our first winter with our TM. With the TM in the driveway and only getting full sun an hour or two a day, the solar panels easily keep the batteries charged. I just have to remember to add distilled water to the batteries ever few months.

Ray

[grill-n-go]

Thanks for your comments. I'm glad I don't make a living writing I really haven't gotten to the stage where I'm ready to consider any one specific panel.

I'm more interested in knowing if I can charge the battery through the DC socket by the fridge. ...and is there a danger of over-charging if I use panels that are bigger than necessary.

Thanks again,

[Caver]

Mario & Idie,

Let's see if Bill and I can respond at the same time again! Bill made some good points and we both agree that your application needs a larger solar panel.

Your question about whether you can charge the battery through the DC connector by the refrigerator is not so simple.

In the 04 and later TMs with the 7345 converter the answer is yes as long as the current doesn't exceed the rating for the connector/fuse.

If you have the 6300 converter, it has a separate output to charge the battery. Since the factory does not give out schematics of these converters I would not want to make a statement about whether this would work or not.

The other option is to wire a solar panel and solar charge controller directly to the battery. Your concern about over-charging the battery is best taken care by using a good multi-stage solar charge controller such as one made by Morningstar.

Do you ever camp without hookups? Ray

[Bill]

Originally Posted by Caver

Mario & Idie,

Let's see if Bill and I can respond at the same time again!

I'm glad we agreed! Nothing is so annoying as having two "experts" post contradictory answers!

In the 04 and later TMs with the 7345 converter the answer is yes as long as the current doesn't exceed the rating for the connector/fuse.

I think the connector is rated for 8 amps - more than enough for a trickle-charge application.

If you have the 6300 converter, it has a separate output to charge the battery. Since the factory does not give out schematics of these converters I would not want to make a statement about whether this would work or not.

I actually bought schematics for the 6300 series, and would be glad to send you a copy. But if you rummage around their web site long enough, you will find them. I am currently "between venues", but in a week or so I should be able to look at the diagrams and give you an answer. Or I can give you a link to the mfr's schematics. Let me know what would help.

The other option is to wire a solar panel and solar charge controller directly to the battery. Your concern about over-charging the battery is best taken care by using a good multi-stage solar charge controller such as one made by Morningstar.

Agreed.

Bill

[Caver]

If you have the 6300 converter you can charge the battery through the DC connector as long as the TM is not plugged into shore power. The relay shown in the schematic isolates the battery from the DC distribution when connected to shore power.

Thanks Bill - there was a schematic on-line. I spoke to the manufacturer a few months ago and they told me they did not provide schematics. I would like to have a 7345 schematic if someone has one.

Ray

[grill-n-go]

Thanks Bill/Ray, you guys obviously know what you are doing. By the nature of my comments you can tell i'm clueless. We do some dry camping and bought a quiet (Yamaha EF3000ise) generator for that purpose. Solar panels are cleaner, quieter, and don't run out of gas. ...and i've had other issues with plastic (Walmart) tanks under the Florida sun.

I'm considering solar panels just as a trickle charger and as a second option as the two of you are doing, a primary source of power. I had hoped to avoid any complicated instalation issues by getting some kind of portable panels that could plug into the DC socket. I really don't want to modify my TM if at all possible because i'm one of those people with the midas touch. From what i'm reading, it's best to get informed and do things the right way. Thanks for your advice, I'll visit some solar panel webistes and weight all my options.