Leisure batteries voltage.

garry55

garry55

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Autocruise Starburst
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From March 2023
Our Autocruise Starburst is fitted with an Eberspacher diesel heater. We have had a lot of trouble getting this to work, but finally it was fixed by a local company. They gave it a full service and replaced one of our leisure batteries (at a total cost of £930) as there was insufficient voltage when not on ehu to run the heater. All this was done under warranty, so no costs incurred by us.
Now, sat on our drive on ehu, the heater works fine. The engine battery voltage is 14.3, and the leisure batteries voltage is 14.1.
If I take it off ehu, the engine battery voltage is 13.9 and the leisure batteries voltage is 13.7.
However, if I initiate the heating sequence, the leisure batteries voltage drops quite quickly to 12.3 volts, which is insufficient to run the heater. I have replaced the other leisure battery with a new (non-lithium) battery and it doesn't make any difference - the voltages remain the same and the heater still won't work.
The 2 new batteries are 80 amp/hr and 75 amp/hr respectively - are these sufficient for powering the heater ?
 
Not an expert but voltage drops when stuff is in use if its high draw and rebounds when the load is removed. The load from the diesel heater will be the glow plug and the draw I think is usually around 4ah at startup depending on model, your batteries should be fine for this. What voltage is it expecting?

Googled, low voltage for the brand looks to be 10.5v so are they sure it's the batteries and not some control module?
 
I think the startup on the heater is more like 10amp, a fully charged battery off load is around 12.7 - 12.9v volts, dropping to 12.3v under load is a little high but not unreasonable.

Do you have a proper multistage charger in the van so the batteries are getting a full charge?

Are you measuring the voltage at the heater or the batteries?
 
Something doesn’t seem right. The amount that a diesel heater draws should drop the battery voltage that much.

Would it be possible to measure the voltage at the battery as well as the heater? I’d be surprised if the heater can’t run on 12.4v but I wonder if the voltage is much lower at the heater than the battery (ie big drop over the wire or a dodgy connection).

Edit: I seem to have asked the same question as Lenny and Paul & Yvette also touched on this.

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garry55 said:
However, if I initiate the heating sequence, the leisure batteries voltage drops quite quickly to 12.3 volts, which is insufficient to run the heater.
Click to expand...
12.3V is a fairly normal voltage for a leisure battery when it's under load. When resting (ie not being charged, not under load) it will vary from about 12.0V (fairly flat but still OK) to about 12.7V (full). When under load (eg a diesel heater starting up) I would expect it to drop a little from the resting voltage, so 12.3V is no surprise.

Those other voltages you are seeing (14.3V, 13.7V) are produced by chargers in the process of charging the batteries, and are not what you would expect to see from the battery when not being actively charged.

The question I would be asking, as others have already said, is what is the voltage appearing at the heater terminals? If it's also about 12.3V, then you have a problem with the heater, it should work OK from 12.3V. If it's less than 12.3V, then you have a problem with the wiring to the heater (bad contact somewhere, oxidised fuse terminals, etc). Or if it's never worked properly, maybe the wire is too thin, and the voltage drop is too much.
 
Thanks for all the replies so far.
The voltages that I have quoted for the leisure batteries have been taken from the Autocruise control panel and I haven't, as yet, taken any actual readings with a multi meter.
I will try and get a reading from the live feed wire at the heater connection point and see if, as suggested, there is a significant voltage drop.
 
If you have the Eberspacher 701/801 type control panel it should show a fault code if it fails to start, there will be a list somewhere in the documents.....

Found this one: https://www.krueger.co.uk/wp-conten...ult-Code-List-for-701-and-801-Controllers.pdf

Common fault on these used to be they would get very sooty if left ticking over for long periods - I used to run a litre of paraffin through once per year to clean the gauze/flame chamber of soot.
 
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2 things spring to mind.
1) the wires running from the battery to the heater are not of sufficient size and causing a larger voltage drop when the glow plug kicks in. You need to measure the voltage at the battery AND at the heater during this phase.
2) The batteries being 80Ah are perhaps a little small? But I honestly doubt this and the fact you have now replaced them twice seems to point in the direction of point 1.

I cannot think of any other reason for a low voltage warning other than a faulty diesel heater which is unlikely.

How long is the wire from the battery to the diesel heater roughly?

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Look at my post from this morning when we started having heater problems off grid - though no issues for the last few days . Mine dropped like yours and the heater failed though with the engine running and coils heated seemed to work fine - though won’t know now as we are not on ehu . It appears that if not driving every day and an overcast day off grid are not conducive for diesel heating
 
AdrianChen said:
If you have the Eberspacher 701/801 type control panel it should show a fault code if it fails to start, there will be a list somewhere in the documents.....

Found this one: https://www.krueger.co.uk/wp-conten...ult-Code-List-for-701-and-801-Controllers.pdf

Common fault on these used to be they would get very sooty if left ticking over for long periods - I used to run a litre of paraffin through once per year to clean the gauze/flame chamber of soot.
Click to expand...
There isn't a fault code displayed on the Eberspacher control panel that I have - the heater itself and the circulation fan spool up on start up but when the voltage dips below 12.3v the heater switches off, although the circulation fan continues to run and blow cold air into the lounge!
 
garry55 said:
There isn't a fault code displayed on the Eberspacher control panel that I have - the heater itself and the circulation fan spool up on start up but when the voltage dips below 12.3v the heater switches off, although the circulation fan continues to run and blow cold air into the lounge!
Click to expand...
On our boats we would try starting the engine to add a bit of oomph from the alternator, but I think if you have 12.3 showing, and the wiring has been sufficient in the past for it to work, you may have a sooty/clogged up gauze etc. this vid gives an idea about what I think needs checking, it shows a replacement, but it's sometimes possible to remove the screen for cleaning.



This site is getting a bit old, but you may recognise the faults they describe - https://www.letonkinoisvarnish.co.uk/eberspacher_faults_1.html
EG. Heater makes two attempts to start, emits smoke for a while or it may smoke heavily and then it stops. Fault code 52.
or
B) Heater makes two attempts to start with no success and then stops completely, no smoke comes from the exhaust pipe.

Good luck!
 
There are solutions available to problems like this. If the voltage needs to be over 12.3V, and the existing circuitry won't supply it, you could fit a voltage stabiliser. They are used for example to provide a supply at 13.8V for a CB radio. The heater will presumably always work if the supply is 13.8V, because that's the kind of voltage level that you get on EHU, and you say it works fine on EHU.

Make sure the stabiliser is capable of supplying at least 10A at 13.8V. It will take power at whatever level the batteries will supply it, and boost it up to 13.8V. Also make sure it is wired right next to the heater, so there is as little wire as possible between the stabiliser and the heater.

For example, the Victron Orion 12/12/18 DC-DC Converter can take any voltage from 8V to 17V, and convert it to a stable voltage of whatever you want between 10V and 15V. So you could adjust it to give 13.8V from any likely input voltage.

But my guess is that there's a bad connection in the wiring somewhere, causing a voltage drop if the amps is high. That needs to be investigated first, I think.
 
Jewellbags said:
Look at my post from this morning when we started having heater problems off grid - though no issues for the last few days . Mine dropped like yours and the heater failed though with the engine running and coils heated seemed to work fine - though won’t know now as we are not on ehu . It appears that if not driving every day and an overcast day off grid are not conducive for diesel heating
Click to expand...
That's another thing - the heater won't operate when the engine is running - should it?
 
garry55 said:
That's another thing - the heater won't operate when the engine is running - should it?
Click to expand...
Can’t speak for your model of heater but we can drive and heat the hab space at the same time
 
autorouter said:
But my guess is that there's a bad connection in the wiring somewhere, causing a voltage drop if the amps is high. That needs to be investigated first, I think.
Click to expand...
I think this is good advice given the voltage drop, and it's a while back that I had a D5 Eber (last boat was a hydronic system but similar), it would normally start and run with quite a low battery (from memory), if the Eber is getting 12.3 it should still go if all is well with the heater I would think. One fault code set is for the glow plug shorting, or the supply wires which may be worth a test (if I knew how) Panels that show the various fault codes are worth having for simple folk like me.....

Edit
Oh 10.5 at the eber that'll do it....
 
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Right - I've tested the voltage of the leisure batteries vs the Autocruise (hereafter known as the AC) control panel values and they are almost (+/- 0.5v) the same. I then started the heater cycle and watched both the AC control voltage and the tester voltage and they again matched as the voltage dropped from 12.8v to 12.2v, at which point the heater shut down.
I then tested the feed wire to the heater at the socket under the van, right next to the heater unit. A resting voltage of 12.6v agreed with the leisure battery voltage displayed on the AC control panel, but when I initiated the heater start up, the voltage at the socket dropped off to ~10.5v despite the AC panel displaying 12.3v. So it appears that I have a voltage drop problem, as most of you have stated. I have no idea where the feed cable to the heater originates from - it just disappears into the floor. I'll start with the electrical control unit - a sort of fuse box with those fancy flip switches / breakers - which is located under the passenger seat but running a new cable from there to the heater looks like a job for a professional installer?
 
You may find the supply cable to your heater is either too thin, too long or has had a joint at some point.
The one in my van came with cables about 8ft long and borderline thickness, I reduced the length to about 2ft and get virtually no voltage drop at all.
Could be worth a rummage to see the supply length etc.
 
garry55 said:
That's another thing - the heater won't operate when the engine is running - should it?
Click to expand...
As it's an Autocruise, I imagine that all your 12V habitation appliances shut off when you start the engine. It's a peculiarity of most UK converters dating from caravan days - long story!

If the heater is run from the same DC distribution board, rather than direct from the battery via its own supply, then yes, it will shut off when you start the engine.

This is a bad idea, because it will prevent the heater doing its proper shut down procedure, unless the installer has done something clever like running the fan supply direct & only killing the fuel pump when the engine starts. That should show as an error code if you start the engine while the heater is running.

If I'm right, then you need to make sure you shut down the heater manually 5 mins before starting the engine. But it could also point to your start-up problem - too much length of too thin wire & too many connections between the battery & the heater. So wiring the heater with a direct fused supply from the battery may solve both problems. You need cable capable of carrying 15A (comfortable margin) over whatever the distance turns out to be with minimal voltage drop.
 
Dazzola said:
You may find the supply cable to your heater is either too thin, too long or has had a joint at some point.
The one in my van came with cables about 8ft long and borderline thickness, I reduced the length to about 2ft and get virtually no voltage drop at all.
Could be worth a rummage to see the supply length etc.
Click to expand...
Thanks for this. Did you replace the original supply cable, or just shorten it? I will be looking at installing thicker gauge cable using the shortest possible run from source to heater, with a 15amp in-line fuse fitted. We have just got back from a few days away and we were glad we were on EHU!
 
No, it's thick enough for a short length and within spec gor the current, but very borderline on a long run.
Being as short as possible can only be a good thing.
And as said above regarding routing of cable, it should ideally be connected straight to the battery, not a switch panel.
Hope you get an easy solution!
 
With a break in the daily rain routine we are suffering at present, I scrambled under the moho to check out the shortest cable run from the leisure battery box to the heater's multi-pin connector. It comes in at ~ 3 feet. Anyone any idea what size (diameter) cable I need to connect straight from the leisure battery + terminal to the heater? I have already procured an in-line fuse holder which I will wire-in in the battery box.

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Just an update - finally got around to installing the new cable. Connected directly to the leisure batteries, with an in-line 15amp fuse fitted.
I used 3mm cable as recommended by Lenny (thanks again!) and now, on start up, the heater unit is only depleting the leisure batteries by 0.3v.
So all is well. And then there is the bonus of being able to run the heater with the engine running, should I ever need to.
Thanks to all who responded and offered their advice (y)
 

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