Chassis Battery Parasitic Load

[CoCoDave]

I posted this on Monacoers too.

I seem to have acquired a parasite on my chassis battery pair. I say "acquired" because I did not check for one at any time prior to this.

The coach has been sitting for about 100 days. During that time I have exercised the generator and the Aqua Hot but not started the main engine. Also during that time the battery disconnect switches have been in the "off" position except for the periods of generator/Aqua Hot exercise.

When I attempted to start the coach the chassis batteries were completely dead. No dash lights and 1.2 volts on the monitor panel. I plugged into shore power for about 7-8 minutes, hit the boost switch and it started right up. I started and ran the generator for two hours and drove the coach about 20 miles.

Following that the chassis batteries were at 12.5 volts with everything off except the battery disconnect switch was still on. I turned the battery disconnect switch off and checked it the following day. The voltage read 12.2 volts on the Fluke DVM.

Then I took the positive cable off the post and put a milliamp meter in series between the post and the cable. It read 112 milliamps. Out in the world a tenth of an amp is not much. Over the span of 100 days it could theoretically be over 200 amphours. But since the batteries' charge would be declining over that time the 112 milliamps would not be constant.

I removed the cable between the disconnect switch and the stud where the battery cable supplies power to the distribution panel. I think that leaves the alternator and starter solenoid as the only two items that the batteries can see. There's probably a contactor or relay for the solenoid and maybe for the alternator too.

Any ideas as to where the parasitic load might be?

Thanks,

[BFlinn181]

It could be a number of things like engine computer, radio memory, clock, very hard to tell. You could put the milliamp meter back in the circuit and start pulling fuses until you find which circuit the draw is in. You might put a solar cell on the roof to keep the batteries charged.

[deSanford]

I put a solar cells on roof solved the problem, and keeps the chassis battery & coach battery fully charged. deSanford

[crazyfox]

112ma draw is in the acceptable range,however over a long period its to much,installing a solar panel would keep the chassis battery up or a shorepower charger wizzard.

[rpasetto]

Some coaches have a bettery maintainer for the chassis batts; some just charge the coach battery when you're plugged in.... assuming you're having this problem when plugged in...

The maintainer (don't remember the brand) went on my 03 Dyn a few yrs ago and after some inquiries I found that one was no longer being made. I replaced it with a Xantrex Echo Charge. I didn't know the maintainer was shot until the solar panel was covered with snow.

[clyon51]

In 100 days, a battery will self discharge without a parasitic load, especially on a starting battery. I would recommend a...

http://www.lslproducts.com/TLSPage.html

This will at least keep the chassis batt charged anytime the coach batts are being charged.

[CoCoDave]

Thanks for the replies.

It turns out that 112 ma is not an abnormally high parasitic load. The coach has a battery maintainer called Keep-It-Up by Lambert. According to their website the parasitic load could be as much as 300 ma.

That's all well and good except that for the battery maintainer to maintain, it has to have power. The coach is not plugged in to anything and as mentioned in the original post both battery disconnects switches were turned off.

Also, the coach does have a solar panel but it's parked under cover so the panel is completely shaded and produces only 3-4 ma of current from the ambient light.

I think there may be something else going on here. Today the chassis batteries were still at 12.5 VDC after charging all batteries day before yesterday and then disconnecting the chassis batteries' at the post.

If they had indeed been drawn down to 1.2 VDC they should have been toast. It turns out that 1.2 VDC is what the solar panel produces when it's parked under the storage canopy. That is what I saw when I looked at the control panel display for the engine batteries day before yesterday when the engine would not start.

I wish I'd have had the presence of mind to check the voltage at the battery posts when the problem was evident.

As suggested over on Monacoers I'm going to cable the house and chassis batteries together when in long term storage. That way when I exercise the generator the chassis batteries will get full current from the charger during the "bulk" and "absorption" phases since the maintainer only transfers single digit amps.

The "something else" mentioned above could be a loose connection. Am going to pursue that line and accept the fact that 112 ma parasitic load does not warrant more troubleshooting at this point.

FWIW

[rpasetto]

I re-read your earlier post. My statement about the maintainer would only have applied if the periods of generator and or engine running had been long enough to to a sufficient charge.

Depending on how long you run engine and genset, the start current draw might be taking away more AH than the running is putting back; checking batt voltage before and after these periods will tell you if the batteries are getting fully recharged. If you are running long enough to fully charge, the 100 days means nothing; each time (how often I don't know) you're starting fresh with fully charged batteries.

On the other hand if each of the the brief periods results in a net loss of battery charge, you'd be drawing them down and would likely see some symptoms of degradation.

The age of the batteries might be a factor here. If they're really old, the self discharge period might be shorter, also you would not have a 450AH bank after a full charge to absorbtion; your capacity might be much lower than when new.

One other factor could be the batt disconnect switches themselves; they could have developed pitted contacts and gove the same symptoms as bad connection.

Hope all this helps and good luck.

[CoCoDave]

Originally Posted by rpasetto

Hope all this helps and good luck.

Thanks Rick. The batteries are three years old.

Since the generator starts off the house batteries and I am not starting the main engine between outings, I was thinking that no load was being put on the chassis batteries.

I will do as you say and check the chassis batteries at the posts before and after periodically running the generator.

Thanks again,

[rpasetto]

Originally Posted by WindsorDave

Thanks Rick. The batteries are three years old.

Since the generator starts off the house batteries and I am not starting the main engine between outings, I was thinking that no load was being put on the chassis batteries.

I will do as you say and check the chassis batteries at the posts before and after periodically running the generator.

Thanks again,

If the problem occurs again, check the voltage at battery and at starter terminals. If there's little difference but nothing happens when a load is applied it's likely there's an intermittent bad connection somewhere... perhaps a terminal a switch contact or evenr the crimp on a cable. Check the ground terminal in engine compt too.

[BFlinn181]

How about a solar panel on the roof of your storage shed? String the cord to dangle from the array to the ground to be plugged in when parked. Being in Washington might effect the efficiency of the panels, they would need to be elevated towards the south probably.

Measuring voltage gain right after charging will give false readings, it takes batteries a time to absorb the charge and 'relax' to real charge state.

[JimM68]

most likely, your bird system is not keeping the batteries tied together, so when you run the genny your chassis batteries are not getting charged. mine drops off when the voltage goes below 12 volts, it is supposed to do that. it doesn't kick back in until the house batteries are very fully charged
The jumpers will get it done for you.

[YC1]

Since it seems your alternator is on the Hot side (battery side) of the cutoff switch as well as the starter I would try to find the alternator wire and move it to the cold side. You could easily have a leaky diode in the alternator. Highly unlikely the starter solenoid would have any leakage in that cable. It would have to be grease or oil or corrosion of some type. I would not want to put the starter side of the wire on the switched side of the cutoff switch. The switch might handle it fine but if the leak is from that wire it would be very easy to figure it out.

Batteries in decent shape will lose a few % each month but should not be dead in three months. If your voltage cratered below 10 volts those batteries are probably cripples and should be replaced. A battery cutoff switch should totally stop the current flow.

[bluepill]

Dave: If you have a bad cell or short in the chassis battery(s), bridging to the house batteries may end up ruining them also by excessive discharge.

How about this:

Fully charge both banks of batteries, including an equalization charge at 14.8 volts.

Disconnect the ground terminal on each battery. You have now isloated each battery from the others as well as any source of draw.

At 24 to 48 hours afterwards test the voltage at each battery. Then test again at 2 and 4 weeks. If your voltages are low, you know that the problem is with the battery.

If all the batteries are good, in the future just disconnect the ground to the chassis if you are going to store for over 30 days.