Leakage current & Charging Question

[JoelP]

Last year I replaced the 2 original coach batteries with a couple of Costco Interstate deep cycle batteries.  No doubt they were less than the best batteries, but I felt that since I rarely boondock these would be good enough.  I have a small solar cell on my RV whose purpose is to maintain the charge.  When I plan to be away from my RV for a week or more I typically turn off the master switch to avoid draining the batteries.  Nonetheless I find that I am draining them faster than I think should be possible.  Unfortunately I cannot leave my RV plugged in while stored.  Yesterday I charged the batteries to the 95% level and this morning they had already discharged to 65% with master switch turned off.  If I leave it for a few days,with the master switch off, I would expect the charge level to go to 10% or less as measured by the meter I have installed to measure the voltage on these batteries. 

I realize that the batteries will not charge when plugged in if the master swithch is off.  It occurred to me that perhaps the solar cell cannot charge the batteries if this master switch is off.  The solar cell is stated to put our 10W of power and I live in very sunny N. Calif where we have lots of sun.  I can see that the indicator light is on to say that I am getting current flow from the solar panel, but it seems it does little to maintain the level of charge.

I am not familiar with what items should remain alive if the master switch is off.  The only item that I know for sure is getting power directly from the battery, without being interrupted by the master switch, is the wieless hub for my TPMS that the manufacturer recommended be hooked directly to the battery and said that it only draws less than 10 MA. It does have one LED light that glows reasonably brightly all of the time, which probably accounts for 5ma all by itself.

Yesterday I check the battery cells with a 4-ball hydrometer and found that most cells were floating 3 balls or a 75% level of health/charge capacity.


I have considered measuring the current flowing out the battery with the master switch off, but have yet to do that.


So for the battery/charging experts on the forum here are my questions:


1.  With the hydrometer reading of 3-balls would that indicate that my 9-month old batteries are already partially cooked from not keeping them well charged all of the time?
2.  Shouldn't the solar cell be able to charge the battery with the master switch off?
3.  Other than the TPMS hub that I mentioned, what iwould you expect to be hooked up to the battery that the master switch would not turn off which could be draining the battery? Is there any easy way to tell?

Thanks in advance for your feedback.

 

[Alfa38User]

2: It depends on where the charge leads connect to the battery system, before the switch or after the switch. I think I would connect right at the batteries to avoid this problem. Is your solar supply adequate* for charging your batteries? Do you have an aftermarket system installed that allows charging the engine batteries from the coach batteries system when plugged in? (My thought is that the solar might be trying to charge both under certain conditions!!)

4: The propane detector is often connected so it cannot be shut off.

* those small panels that came with some models of Winnebago are seldom much use for battery maintenance according to many others more familiar with them, (too small).

 

[Gary RV_Wizard]

Alfa38 covered the main points well.  A 10W panel is probably no more than 600 ma at peak output and often much less even in the sun.  And it may or may not be wired to bypass the master disconnect.


The propane and possibly the CO detectors do indeed bypass the Master switch (wired direct per RVIA standards). The electric steps, however, should be wired to the chassis 12v,  not house. Often the leveling system and slides bypass the Master as well, but they should be zero draw if not actually running.

Why not wire the TPMS to the chassis battery rather than house?

I doubt if your batteries have been harmed yet.  As long as you keep an eye on them and charge up occasionally, there is little harm.

 

[JoelP]

2: It depends on where the charge leads connect to the battery system, before the switch or after the switch. I think I would connect right at the batteries to avoid this problem. Is your solar supply adequate* for charging your batteries? Do you have an aftermarket system installed that allows charging the engine batteries from the coach batteries system when plugged in? (My thought is that the solar might be trying to charge both under certain conditions!!)

4: The propane detector is often connected so it cannot be shut off.

* those small panels that came with some models of Winnebago are seldom much use for battery maintenance according to many others more familiar with them, (too small).

This solar panel system is the stock solar panel provided by Winnebago when it was new.  I think I need to go find that schematic and see where it connects.

I noticed today that even when I set the switch at the front (which powers the radio and 12 volt port) from house to chassis battery that it remains powered regardless of whether I switch off the chassis battery, so that is drawing power beyond those two switches.  Of course the steps are unaffected by these switches, but should draw nothing if not in use.

I would be less inclined to hook the TMPS hub to the chassis battery since I would not like any chance it could run down that battery and I would be stranded.  I just wish there were a true master switch for everything.

 

[Gary RV_Wizard]

Just put a manual battery switch on the negative (ground) terminal. A old-fashioned knie switch, one of these post clamp models, or a rotary type switch.

 

[JoelP]

I disconnected the positive terminal and measure the current out of the battery with nothing turned on versus nothing turned on an the main switch off and in both cases I measure only 1.4mA.  This cannot be discharging my batteries.  I have to believe it is internal battery leakage.

 

[Gary RV_Wizard]

Batteries will indeed self-discharge, faster in warm humid environment and less when dry and cool. Still a tiny amount, but overtime it becomes noticeable.

More about that at:  http://batteryuniversity.com/learn/article/elevating_self_discharge

 

[JoelP]

I cleaned my solar panel and now am seeing the charging beginning to work to overcome this internal leakage.