Why is my chassis battery discharging?

[TQ60]

Operating the switch makes a difference and you see no voltage past switch.

Tip...switch closed is connected and allowing current to flow and open is not connected not allowing current to flow.

Try this, can you disconnect cable at switch or for starters lift positive cable.

We have seen bad amp meters that give this indication.

You can test the calibration of your meter and all you need is any vehicle lamp, better is one with wires.

Follow these instructions and we will use made up numbers for demonstration.

Ohms law is volts = resistance times amps.

So switch your meter to ohms and measure the resistance of the bulb.

Write that down.

Now measure voltage at battery and write that down.

Now divide the voltage measured at the battery by the resistance of the bulb.

Say voltage as 12 and ohms was 6.

12 / 6 =2

So 2 amps would be expected.

Now reconfigure your meter for amps then with some help hold the lamp on one battery post and use your amp meter as a jumper wire to connect other post of battery to other connection on bulb.

Testing the battery should not matter unless it is a magic battery that can make a connection.

If you draw a large circle then on one side draw a box on the line and other side draw a circle on the line.

Box is battery and circle is a lamp.

Now draw an X on any part of the circle and that is your switch.

You have something creating a path around your switch and it is a fairly good amount

If switch next to battery then assuming you can follow the wire completely but there must be something going on.

Is the battery clean as crud on a battery can carry current.

[Monacoach]

Originally Posted by bill06447

If the battery isn't connected to anything and it's discharging then its a bad battery. They can and do short internally. Always a good practice to replace all the batteries in a bank when one fails-not doing so is like replacing one cell in your 3-cell flashlight, soon the others will be dead.

Do you think the amp reading that im getting is coming from within the battery? Perhaps the discharge rate of a bad battery measured in amps?
Sounds logical to me. I will be buying a pair of batteries. Im only holding onto this one to do some testing.

[Monacoach]

Originally Posted by TQ60

Operating the switch makes a difference and you see no voltage past switch.

Tip...switch closed is connected and allowing current to flow and open is not connected not allowing current to flow.

Try this, can you disconnect cable at switch or for starters lift positive cable.

We have seen bad amp meters that give this indication.

You can test the calibration of your meter and all you need is any vehicle lamp, better is one with wires.

Follow these instructions and we will use made up numbers for demonstration.

Ohms law is volts = resistance times amps.

So switch your meter to ohms and measure the resistance of the bulb.

Write that down.

Now measure voltage at battery and write that down.

Now divide the voltage measured at the battery by the resistance of the bulb.

Say voltage as 12 and ohms was 6.

12 / 6 =2

So 2 amps would be expected.

Now reconfigure your meter for amps then with some help hold the lamp on one battery post and use your amp meter as a jumper wire to connect other post of battery to other connection on bulb.

Testing the battery should not matter unless it is a magic battery that can make a connection.

If you draw a large circle then on one side draw a box on the line and other side draw a circle on the line.

Box is battery and circle is a lamp.

Now draw an X on any part of the circle and that is your switch.

You have something creating a path around your switch and it is a fairly good amount

If switch next to battery then assuming you can follow the wire completely but there must be something going on.

Is the battery clean as crud on a battery can carry current.

Might not be squeaky clean but I will give it a wipe. You seem to know your stuff. Ok rather then disconnecting from the switch I will remove pos cable from the battery and see if that changes the amp measure. I will do this on Friday when I return to the coach. That also gives me some time to read your post again and try the light bulb test.
Thankyou for the help. Thankyou to all others for your help.

[Mudfrog]

I believe you stated that the amp draw increased when the battery disconnect switch was open. Could the switch be leaking voltage through its mounting bolts? Possibly something broken inside the switch which is allowing positive voltage to reach the frame? Maybe the switch housing itself is cracked or burnt and is allowing contact with the frame?

[nothermark]

Originally Posted by Monacoach

Ok surface charge doesnt change anything. I was wondering about that. Now you mention isolating circuits yet the battery is not powered to anything. So isolating circuits is pointless on an isolated battery isnt it? Could the 2.18 amp draw be tge battery drawing itself down? Perhaps the measure of a bad battery discharging?

The internal resistance discharges internally. It can be determined by calculation but not really measured. It takes a complete circuit to pass current including the meter you are measuring it with. That is what has me puzzled. Since I cannot see your setup I do not know what is going on. You might want to look for a path from the positive post to your meter to the negative post of the batteries. There has to be one or you could not be able to measure the current. Trust nothing, start by disconnecting anything left on the positive post if you are measuring the current through the negative lead.

[Monacoach]

Originally Posted by Mudfrog

I believe you stated that the amp draw increased when the battery disconnect switch was open. Could the switch be leaking voltage through its mounting bolts? Possibly something broken inside the switch which is allowing positive voltage to reach the frame? Maybe the switch housing itself is cracked or burnt and is allowing contact with the frame?

The amp measure increased by .30 of an amp when I ser the switch to allow current to the coach. Interesting point about the frame. Im looking forward to getting back to the coach to do more testing.

[Monacoach]

Originally Posted by nothermark

The internal resistance discharges internally. It can be determined by calculation but not really measured. It takes a complete circuit to pass current including the meter you are measuring it with. That is what has me puzzled. Since I cannot see your setup I do not know what is going on. You might want to look for a path from the positive post to your meter to the negative post of the batteries. There has to be one or you could not be able to measure the current. Trust nothing, start by disconnecting anything left on the positive post if you are measuring the current through the negative lead.

Yep that is what I will do. Also I will connect the negative cable and remove positive cable and measure with amp meter to pos post.

[bill06447]

Originally Posted by Monacoach

Do you think the amp reading that im getting is coming from within the battery? Perhaps the discharge rate of a bad battery measured in amps?
Sounds logical to me. I will be buying a pair of batteries. Im only holding onto this one to do some testing.

I've witnessed bad batteries reverse polarity under load. I'm also a bit puzzled on the comments about disconnect switches if the battery isn't hooked up to anything? or have I missed a portion of the discussion

[Monacoach]

Originally Posted by bill06447

I've witnessed bad batteries reverse polarity under load. I'm also a bit puzzled on the comments about disconnect switches if the battery isn't hooked up to anything? or have I missed a portion of the discussion

Basically the battery is not hooked to the coach because the negative cable is removed and the positive cable is hooked to the disconnect which is in disconnect position.
I have heard that I can remove the positive cable to check amp draw which is strange to me because I thought the amps travel through the pos cable.

[RogerRoll]

Originally Posted by Monacoach

Basically the battery is not hooked to the coach because the negative cable is removed and the positive cable is hooked to the disconnect which is in disconnect position.

I have heard that I can remove the positive cable to check amp draw which is strange to me because I thought the amps travel through the pos cable.

Your ammeter is not a 'clamp-on' so it is connected EITHER between the Neg post of the battery and the ground cable that is normally attached there OR between the Pos lug of the battery and the red cable going to your disconnect. The ammeter completes the loop circuit. If the loop is open anywhere, current will not flow! It will read the same current regardless of where it's connected (neg or pos).

My money's on the disconnect switch. There's probably an internal leak to ground due to corrosion or damage to the coil.
Have you tried taking the small wires off the disconnect coil to test? One of them could be at fault.

Good luck!


2010 Winnebago Aspect 28B

[nothermark]

As has been said your meter is part of a loop. It can be anywhere in the loop but the loop is a closed current path. If all you are connected to is an insulated post and you are passing current the post insulation is failing. There has to be a current path.

[Monacoach]

Sorry had a brain fart..makes sense that the amp meter connects the circuit. No I haven't done anything with the dis switch other then checking with test light.
I will tinker with it tomorrow and see what I can do. Im hoping that simply replacing the batteries and putting them on a battery minder will solve the problem but we cant always be tapped into shore power so I hope to verify and fix any kind of excessive drain.

[YC1]

Originally Posted by YC1

Take the switch apart. Leave it unmounted. There is some leakage to ground or through it. If it is not a corrosive type build up to ground that is causing the drain the switch is shorted and allowing current to flow. Finding the 2.5 amp draw after that should not be difficult. But always fix the obvious first and often times other things go away.

Again, it is impossible to have current flow without a complete path. The positive is indeed going somewhere. Cutoff switches are known to fail. Be sure to take the negative of both battery banks off when you inspect the switch.

Replacing the battery will not fix the problem. It has nothing to do with current draw other than being the supplier of it.

Please, take a picture of the switch. If you can disconnect the wire that goes from the switch to the rest of the rv and your current stops, the switch is bad. If the current stays, the switch is bad. These switches can fall apart inside.

You are chasing two or three problems here and not just one. Yes you battery may be toast but that is NOT the reason for the current drain.

With that much current draw a test light as suggested by TQ will confirm you are using the meter correctly. Just put it inline with either lead of the battery just as you did the meter. There is enough current draw to make it light. If it does not light I can suggest a couple of tests to confirm your meter is working ok.

[Monacoach]

Ok I will do the test light thing tomorrow. Question:::
With test light on the battery side of cutoff it lights up.....on the other side it does not light up. If I switch cutoff to allow current the test light lights up. Does this not confirm that the cutoff switch is working correctly?