Battery charging

How would a person with no knowledge (me) who owns a 1996 TM that has had several owners know if the tandem batteries that came with this unit are able to charge when hooked up to AC. We generally hook up to a charger before traveling.
Cheri

Cheri

In summary, I don't know of any easy, simple way to tell the condition of a TM battery using the OEM meter under the sink or any other way. You are guessing. You will run the battery dead sometimes and be surprised when it happens. You won't really know when it is charged and will unplug from shore power after a few days of charging. You will have to regularly check the water level in your batteries.

I believe you have the same converter that I had in my '04. As I recall, it was named Magnatec 6330. That device puts out about 6 Amps charging current and slowly drops to something like 2 Amps. The result is the battery requires days to charge, water continually bubbles for weeks and water is depleted if you stay connected to shore power. For this reason, the TM should not be left plugged into shore power.

To begin to know the state of charge in your battery, you need a current meter in the line to the battery. This is best accomplished using a "shunt" or low resistance in series with the battery. A digital voltmeter reads the (small) voltage across that shunt to determine the current.

To determine if your battery is being charged, you should be able to look at the voltage across the battery when connected to shore power to get a rough idea of what is going on. You will see somethign like 13.8 Volts if it is being charged. But it is a very rough idea, indeed.

For state of charge (percent charged), The battery voltage can be measured 20 minutes after disconnecting all loads (lights, etc) and shore power. The voltage mesured at that time can be compared to charts to get a rough idea of relative charge level. I can get you some links to reference the expected voltages if you would like that and it has been discussed on this forum.

To be truthful, all of these are very rough indicators. Since my wife cannot tolerate extreme cold temperatures, I became so obsessed by this problem that I purchased and installed the Xantrex Link 10 battery meter which works like the gas guage on your car. It reports current consumed (Amp hours) and time remaining at current discharge rate (hours). This is the mechanism used by the expensive RVs, large boats, and homes operating off the power grid. Its a bit of overkill, but I couldn't find anything more appropriate. With this, I can set the camper for night-time operation (furnace on, lights off) and get an immediate indication of the hours the battery will support this operation, including the current state of charge. Then, knowing the furnace is on half the time or 1/8 of the time, I can project whether the battery will last the night.

Your solution of using a "battery charger" is a good one. The charger has a meter showing the charge current and that is not available in the TM converter. When the charger current drops to 1 or 2 Amps, the battery is charged. FYI, my obsession with this charging problem drove me to install the PD9160 converter which can be left plugged into shore power and actually protects the battery from going dead, overcharge, and sulphation.

Again, there is no simple, low cost and reliable solution to this issue.

Thanks for your response. It looks like the best way is to continue to charge with the charger since we really don't know how much charge has occurred or if we might be over charging. How does that not become a problem when you have full hook ups and are camped, say for a week or more? Do you have to check water in the batteries when you camp with hook ups for extended periods? I'm sorry if these are dumb questions.
Cheri

[Bill]

Bob is pretty much right, but in the interest of completeness, I will point out that there is, in fact, one reliable way to determine a battery's state-of-charge. That is a temperature-corrected hydrometer, available at any auto-supply store for a few bucks. It measures the strength of the acid in the battery cells, which is directly proportional to state-of-charge. But it is messy and unhandy to use. It looks like a turkey baster, and operates the same way - a rubber bulb on top of a long tube with a narrow nozzle. You stick the nozzle into a battery cell, and suck up enough liquid that a little glass float inside the large tube floats. The float has markings on it that tell you the answer. If the float barely floats, your battery is very weak. If it floats high up in the liquid, your battery is charged. In between is, well, in between.

When you have taken the reading for one cell, you squirt the liquid back into the cell, and repeat the process for the others (a total of six cells). Problem is that the liquid you are sucking and squirting is battery acid. It can be nasty stuff (burns holes in clothes very quickly, for example, corrodes metal, is hard on the skin, and would REALLY burn your eyes). And no matter how hard you try, it tends to get everywhere.

The only good things about a hydrometer are that it is cheap and accurate. Few people use them because of the mess, but it might be a good solution for an occasional use as you are trying to determine if your batteries will accept a charge.

I like Bob's approach - the Xantrex meter - A LOT, and I will admit that I covet one. As he said, they are kinda pricey, so I haven't done it yet. But again as he said, everything else is a pretty rough indicator. Practice will help you recognize and evaluate what is going on with your battery, but that takes a while.

Bill

[B_and_D]

This is what I use to test our battery charge (I have two 6V T-105's connected together)
http://www.realgoods.com/renew/shop/...603/ts/1026111

and one of these: http://www.cetsolar.com/voltmeter.htm

I connect one end of the clamp onto the positive terminal of the battery, and another to the end of the clamp to the negative terminal of the other battery. I connect them at the positive & negative terminals where they are connected to the TM wiring. Then I insert the digital volt meter into the outlet.

Do you also have two 6V batteries, or do you have two 12V batteries connected?

What I do is turn off the AC power, and then check the batteries after they have rested for a while (half an hour or so).

I don't leave the batteries connected to shore power for more than a couple of days; if we're going to be staying put somewhere for longer than that I take apart the inline 12V fuse near the batteries (and hope that I don't lose the fuse itself). I have several replacement fuses in the TM, just in case, if you buy some make sure that they're not only the correct amps but the right length. If you're going to be using the TM often and hooking up & unhooking, you might want to check the water once a month. One of my next projects (where do they end?) will be to install a battery cutoff switch. I bought one from Camping World but I'm not happy with it because it has too much exposed, unshielded metal (to me it looks like a nasty shock waiting to happen).

This works well for us, so far, and it's not expensive.

Hope this helps.

Dee

I believe that I have 2 12 volts. Thanks for the info. This is so not my department
Cheri

Bill is correct on the Hydrometer, but it's only accurate when the battery has been charged and jostled around to mix in the water you just added. You will get a false reading if the acid and water haven't had time to mix. In our shop we always checked batteries with a hydrometer (actually with a prismatic tool that you only use a drop of acid) and a load bank. A load bank puts a load on the battery through an adjustable carbon pile. The fully charged battery is loaded to a specific amount based on the amp/hour rating and you watch the voltage drop for 10 seconds. It should not drop below about 10.6 with this load. If it does, the battery is weak and will probably fail soon. Of course after testing a battery this way, it must be recharged. Many parts stores will check your battery for you if you think it's not taking a full charge - be wary though, they sometimes will tell you the battery isn't any good so they can sell you a new one. Watch them test it if you can. The best place I have found to get a suspect battery checked is Interstate Batteries - batteries are their business! A good place to find out more than you ever wanted to know about Lead/acid batteries is: http://www.batterystuff.com/tutorial_battery.html
All the equipment we maintained in our shop we changed over to "gel cells" which have no liquid acid and therefore never need water added. Since we shipped vehicles world-wide, this cut down on a lot of certification for the aircraft loads. (I was in the Air Force and Air National Guard) The absorbed glass mat batteries were also very good for no maintenance.