Getting Shocked from Coach Battery

[peteco]

I have gotten a noticeable shock while working on my coach batteries. It occurred while disconnecting the terminals, and also when I touched the metal tiedown. This occurs when it is not plugged in to 120v. Any suggestions on what is causing this?

Pete
2006 Roadtrek 210

[booster]

Originally Posted by peteco

I have gotten a noticeable shock while working on my coach batteries. It occurred while disconnecting the terminals, and also when I touched the metal tiedown. This occurs when it is not plugged in to 120v. Any suggestions on what is causing this?

Pete
2006 Roadtrek 210

Was the inverter on?

[Bruceper]

You have a ground fault. I suggest you disconnect the battery and get it looked at soon. Ground faults can cause fires.

It does not happen when plugged into 120 as the system is grounded.

[peteco]

Originally Posted by booster

Was the inverter on?

When I got shocked the inverter switch was off. What I don't remember is if the battery connect switch was on. So there may have been battery power to the TrippLite inverter/charger.

I just charged the batteries using the inverter/charger. I then turned off the charger. I measured about 3 volts between the battery hold down strap and the van body. I also put the meter lead on the battery body and measured voltage as well. I was curious if there was any current but only measured about 1 mA. Then I checked the voltage again between the hold down strap and the van body and it was 0 volts. So had I bled off some kind of surface charge???

[peteco]

Originally Posted by booster

Was the inverter on?

I found this interesting comment in John Slaughter's Notes on Roadtrek Electrical Simulator
http://www.metrotrekkers.org/utility/notes.pdf

"In the 2006-2007 time period, Roadtrek began implementing a wiring change. Rather than connecting the inverter/charger directly to the 12 volt fuse panel and loads, it was connected to the battery bypassing the battery disconnect switch. The battery disconnect switch now disconnects the 12 volt panel and loads from the battery and the inverter/charger.
The obvious operational characteristic is that the 12 volt panel will be powered only when the battery disconnect switch is on even if plugged into AC mains power.
The not so obvious operational characteristic is that the inverter will operate even if the battery disconnect switch is off. Many owners have run down their RV battery because they left the inverter switch on."

I'm not sure if I have the old or new setup in my 2006 RT. If new, then the inverter is on according to this.

[booster]

Originally Posted by peteco

I found this interesting comment in John Slaughter's Notes on Roadtrek Electrical Simulator
http://www.metrotrekkers.org/utility/notes.pdf

"In the 2006-2007 time period, Roadtrek began implementing a wiring change. Rather than connecting the inverter/charger directly to the 12 volt fuse panel and loads, it was connected to the battery bypassing the battery disconnect switch. The battery disconnect switch now disconnects the 12 volt panel and loads from the battery and the inverter/charger.
The obvious operational characteristic is that the 12 volt panel will be powered only when the battery disconnect switch is on even if plugged into AC mains power.
The not so obvious operational characteristic is that the inverter will operate even if the battery disconnect switch is off. Many owners have run down their RV battery because they left the inverter switch on."

I'm not sure if I have the old or new setup in my 2006 RT. If new, then the inverter is on according to this.

Our 2007 190 is wired as he describes. I think they did the change at the same time as they went from an isolator to a separator. The main reason of the changes, again a guess, was that they didn't want folks to have to remember to have the 12 power on when the plugged in to shore power if they wanted the batteries to charge. They also charge the starting battery with the system. I don't think any 2006 units were done this way, but not sure.

I haven't tried it, but I would certainly think the inverter would run with that system. Even with the inverter and the switch off, the charger will pull some current at plug in and spark a bit. I don't why it would be enough to get a shock though, as that has to be much higher voltage.

[peteco]

Originally Posted by Bruceper

You have a ground fault. I suggest you disconnect the battery and get it looked at soon. Ground faults can cause fires.

It does not happen when plugged into 120 as the system is grounded.

Any suggestions on how to check for a ground fault?

[peteco]

Originally Posted by booster

I think they did the change at the same time as they went from an isolator to a separator.

I have an isolator.

[booster]

It has been a while since I looked all that stuff up exactly, but as I remember it as follows, others may have more information.

For the AC, the neutral and ground should not be bonded within the RV, they will only show connected when you are on shore power, because they are bonded there, and I think most generators will bond them when they are running through the transfer switch.

TEST-With no AC power on the van, inverter off also, you should see no continuity between neutral and ground at the outlets.

The AC separate ground wire should not be attached anywhere to the chassis of the van, and only connected at the AC devices like the charger and the outlets.

TEST-Check for continuity between the AC separate ground and the metal van chassis, there should be none. As long as there is no AC power, you can also check the neutral to the chassis, and that should also have no continuity.

The 12v side will have the negative to the van chassis on all the stuff, as well as any separate grounds like on the charger. 12v shouldn't shock you, though.

The only thing I can think that would put some 110v AC on the chassis would be if one of the appliances or outlets has failed and is leaking to its frame (like the microwave) and charging up the chassis while plugged in, but it should charge all of it, so you wouldn't get a shock between the metal parts, only to the ground.

Very mysterious indeed.

[DAWg134]

You stated that you were disconnecting the battery terminals, but didn't mention how you went about doing so. If you attempted to disconnect the positive terminal before disconnecting the negative, then it is quite possible you received nothing more than a 12 Vdc shock. This would occur because you were using your body to make an electrical connection between the battery voltage and grounded metal tiedown.

Yes, a 12 Vdc shock is indeed quite noticeable.

[booster]

Originally Posted by DAWg134

You stated that you were disconnecting the battery terminals, but didn't mention how you went about doing so. If you attempted to disconnect the positive terminal before disconnecting the negative, then it is quite possible you received nothing more than a 12 Vdc shock. This would occur because you were using your body to make an electrical connection between the battery voltage and grounded metal tiedown.

Yes, a 12 Vdc shock is indeed quite noticeable.

I must be made of Bakelite, because in 50 years of working with automotive and industrial equipment, I never have gotten a shock from 12 volts. I also don't ever remember anyone else getting one, either. A huge part of electrical troubleshooting is unplugging or plugging in 12v hot side connections and you invariably touch them and surrounding ground surfaces. It is also very common to squeeze the probe of a voltmeter against a loose 12v spade or ring terminal, or wire end, to get good contact. Again never a shock.

Perhaps if you had wet, salty, hands and very tight and big area contact, you might get a tingle through one hand. Kind of like putting a 9v battery on your tongue to test it.

Ignition wires, on the other hand, will definitely get your attention, as will a fully charged ignition coil even with the engine off.

[AK49er]

Bakelite here too!

[DAWg134]

I think the probability of getting a perceptible shock results from a combination of a) skin moisture/salinity, b) proximity, and c) voltage levels.

Pete had just charged the battery so it was probably sitting there with a surface charge of 14-15 volts. If his hand was sweaty and his palm bridged the terminal to the hold-down clamp, then it would be enough to deliver a noticeable shock - nothing like grabbing a pair of 120 Vac leads, but a noticeable tingle nonetheless.

I've been working on automobiles nearly as long as Booster and have only been shocked twice, so apparently the necessary conditions for occurrence are fairly rare. However, twice was enough that I now always disconnect the negative terminal first.

As kids, we would occasionally dare one another to touch the terminals of a brand-new 9v battery to our tongues. I still use that technique to quickly check the condition of 9V batteries... but only if I'm reasonably certain it's at least partially discharged.

[peteco]

I have been shocked a couple of times. Once was touching the metal battery hold down. Not sure why that is. Since then I work on the battery with gloves on.

[avanti]

I'm pretty sure that it mostly has to do with sweaty palms or equivalent.

P.S. -- Just as a reminder, don't forget the golden rule of battery work: Take off all jewelry. There have been truly horrendous accidents involving car batteries and rings.