A tricky problem

stewartthorp · November 2019

My camper which has a split charger and solar seems to have a problem. When starting the eberspacher the voltage drops to 10.4 volts and it stops working. All three new AGM batteries are fully charged.

Disconnecting the leisure batteries the battery voltage still shows 12.6 volts?? Could the starter battery be leaking through to the leisure battery set up? maybe messing with voltage sensor.

Could the spilt charger relay be sticking ?? Starter and leisure batteries both charge well when driving.

Thanks to anyone if they have any ideas.

BB. · November 2019

Welcome to the forum Stewart,

I guess you are talking about an RV heater--And it probably does not draw more than 8-10 amps normally @ 12 VDC. (not sure about diesel heaters--The ignitor may draw much more current while starting).

And you are somewhere in the UK.

Has the heater+battery configuration worked before--And now it is failing? Or did it always have "issues"?

When you are seeing the 10.4 volts... Is that at the heater DC input terminals, at the house battery bus, or at the RV chassis battery (engine start battery--Assuming this is an RV on a motor chassis of some sort)?

Using your voltmeter, measure the voltage (under load) at each of these major points. If the low voltage is at the heater, then probably loose/corroded wiring connections and/or flexing/failing cable (look for brown/black/burned spots at the terminals and along the wire--Especially where it may flex and/or go through a punched sheet metal hole (does hole have sharp edges removed or protected?).

If the low voltage is at the house battery and not the chassis battery--Then check battery terminals/wiring (tight/clean). Generally, you should only see voltage drops like that with high current draw (engine starter of something like 50-100 Amps).

If you see both the chassis and house battery voltage drop, then it would sound like the isolation relay is "welded".

A very handy tool for debugging is the DC (+AC) current clamp DMM (digital multimeter). You can clamp a single wire and see how much current is flowing, and where it is coming from (one battery, whole battery bank, +chassis battery, etc.). In the US, the meters run from $50 to $100 for cheap to moderately priced (and >$300 for Fluke).

https://www.amazon.co.uk/s?k=dc+current+clamp+meter

Note, there are AC only current clamp meters (perfectly good, but do not measure DC current--our needs)... And there are AC+DC current clamp meters... Pay attention to the descriptions, most AC clamp meters have an AC+DC voltmeter function too... And that can be confused with the AC+DC current clamp function (plus AC+DC DMM function) you are looking for. Sometimes you have to zoom into the meter face and make sure that it had AC + DC current mode settings.

-Bill

Estragon · November 2019

I have an espar on my boat, and I don't think the startup draw is particulary high. A small fuel pump starts dosing the heater, it tries to ignite (sometimes takes a few tries), with the blower barely running during the startup cycle(s). Only once it's sucessfully lit, the blower ramps up. IIRC, mine takes ~4-5a at max blower speed.

Like Bill suggests, a wiring issue sounds most likely. Is there a separate negative return wire, or is it chassis ground return?

stewartthorp · November 2019

Thanks. The voltage near on my lights and eberpacher is 10.4 but on the battery terminals it doesn't drop below 12.5. The voltage on the batteries not under load is 12.9v.

The eberspacher and lights worked well when i got the van three years ago. It is an expolice van (It is 20 years old...)

So from the you description there is an earth somewhere which is not good. The same thing happens when I turn lights on or turn the eberspacher.

My problem I think is going to be finding where the poor earthing/ corrostion problem is happening. The van was custom built for the police so everything is very tidely hidden away.

I tried running a positive line directly from the liesure batteries to the eberspacher switch and it still showed the same massive voltage drop - hence a poor earth issue.

Ive made a mistake of buying a AC clamp meter instead of a DC ammeter..

This is my van when it was in operation. fyi the windscreen guard has been removed#

Ill keep you posted

BB. · November 2019

Chassis returns, yes they get corrosion and/or loose.

With a load on your system, take your dmm and measure the voltage drop across each wire and connection. With that much drop, it should be pretty obvious.

You can also connect one lead to a fixed location (battery terminal, your heater ground, etc.) and take the other lead and move it down there current path until you find a bigger jump.

Frequently, if the current flowed between body parts, hinges, or from sheet metal to frame, there is a jumper across the joint for reliable current flow.

Bill

stewartthorp · November 2019

Thanks Bill. I'll have a look for a dodgy earth.

BB. · November 2019

Also, running a cable from the "local chassis ground back to the battery negative bus (sized to carry 100% of the total return current) would work.

Also, for anything that has a specific negative/return lead, carry each one back to the battery negative bus.

For solar power systems, we always recommend full hot and return wiring and not to use local chassis ground connections.

Bill

stewartthorp · November 2019

Thanks Bill

I see you have provided help to lots of people.

I'll try to find the earthing points linked to the chassis.

Estragon · November 2019

Personally, I'd just run the negative return wire(s). Chasing down the chassis issues would likely be more trouble than it's worth (at least for me), and the Espar shouldn't need particularly heavy wire.

BB. · November 2019

One thing to worry about, if the heater (any heavy load) is mounted to, for example a door, you want a bonding wire jumper or home run return cable.

Current through hinges can cause corrosion or even spot weld them as the load current passes through them.

Hope you get this all sorted soon.

Bill

stewartthorp · November 2019

Hi Bill. Just fixed the problem.

Earth was bad. Left it where it was and earther the leisure batteries to another interior preinstalled ground. (thanks to police out fitters)

Lights and eberspacher work fine now - no massive voltage drop..

I used an old jump starter cable as the new earth.

Thanks again.
Next project is upgrading my 70W solar to an additional folding 120W solar rig which can be stored in vehicle when not needed.

The 70W keeps batteries topped up when not off grid.

A tricky problem

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