Diesel Heater - Low voltage?

[Tim Good]

I can't seem to power up my Webasto without the engine running or show power plugged in and charging the batteries since I get a low voltage warning. I did manage to get it working at anchor the other night by starting the engine and then the Webasto and then turning the engine off.

Does anyone else have this issue of not being able to start it up on the batteries alone even when they are full and kicking out a good 12.7V.

From my limited knowledge I am getting 12.7V at the heater in the aft locker.

 

[prv]

Did you measure the 12.7v at the heater with it running (ideally during startup), or with it off? I had an equivalent issue with my fridge, where the supply at the compressor (when not running) seemed to be giving a healthy voltage. But in fact the connection was very poor (loose bolt in a ring terminal), and when it tried to draw any significant current the voltage plummeted. I strongly suspect you have the same problem.

A quick way to check would be to temporarily run a length of substantial cable direct from the batteries to the heater. If it then works, you can start hunting for the problem in your existing wiring.

Pete

 

[pvb]

Has it previously worked OK? I ask this because I think the boat is relatively new to you, isn't it? And didn't you post recently about having strange voltage issues with your batteries?

 

[Tim Good]

Has it previously worked OK? I ask this because I think the boat is relatively new to you, isn't it? And didn't you post recently about having strange voltage issues with your batteries?

Good memory! Ok so the battery problem was down to a loose connection on one of the batteries that seemed to cause a charging problem and causes a smell when the shore power starting throwing in a good ampage. All fixed now and I think I caught it in good time that the batteries were not too damaged.

I think PRV might be right so I'll test again at the unit during startup.

 

[lw395]

It will draw a fairly high current to ignite.
At switch-on the glow plug is cold and draws more current until it hearts up.
It needs fairly stout cables to avoid voltage drop.
Also any poor connections will be a problem.
I have a test-load which draws 10A, that shows up problems quite often.
You could use a couple of car headlight bulbs or a big spotlight.

Also, a part charged battery may show 12.7V off load, but drop a lot under load. Particularly if that 12.7V is partly surface charge from recent charging.

At least you know it's all about volts and you are not confusing it with air-in-the-fuel start up problems like I had.

 

[ex-Gladys]

Agree with what's being said here... All the potential issues being described such as monitoring the voltage at the heater when starting are really good. I don't have a heater, but have a Wallas Diesel Cooker (same principle), and the idiot installer wired it to 15A boat electrics at the end of a 10m run from the batteries... Manufacturer's instructions are wire direct to battery with thick cable, even though the glowplug only draws about 8A for about 2 minutes. With the original installation I frequently got low volt alarms. Haven't had one since I did the sensible rewire...

 

[David2452]

From memory you have an old DW80 which were a bit more susceptible to lower voltages than modern marine rated units so that will be a contributory factor but it should still fire up at around 12v (provided you have current as well) As has been said, check the voltage at the heater whilst the glow plug is pulling power, typically on a DW this will begin around five seconds after switch on and continue for around 15 - 20 seconds, unlike the air heaters it will be a continual draw rather than a pulsed one.

 

[pvb]

Good memory! Ok so the battery problem was down to a loose connection on one of the batteries that seemed to cause a charging problem and causes a smell when the shore power starting throwing in a good ampage. All fixed now and I think I caught it in good time that the batteries were not too damaged.

I think PRV might be right so I'll test again at the unit during startup.

But we still don't know whether the unit worked OK previously, or if you simply inherited a bad installation.

 

[NUTMEG]

Funny how this forum works isn't it. I had exactly the same issue on Saturday night. About seven in the evening crew moaning about being chilly so I went to fire up the Webby AT3500. Went ashore to walk the dog and got back aboard to a near mutiny as the heater had failed to start. Two new this year house batteries (240amphr) and fully charged as had just motored 30 miles or so. Low Voltage error flashing. Started the engine (on the same batteries) and retried the heater and bingo, it fired up. Shut the engine off and it purred away to itself until one AM when I went to bed.

Will look at the weight of the supply cable, joints etc but pretty sure all is well.

 

[Tim Good]

But we still don't know whether the unit worked OK previously, or if you simply inherited a bad installation.

I inherited it but I rebuilt the unit from scratch with plenty I advice from David above. It now all works all ok but it would be nice for it to work without any power source like the engine or shore.

 

[Tim Good]

From memory you have an old DW80 which were a bit more susceptible to lower voltages than modern marine rated units so that will be a contributory factor but it should still fire up at around 12v (provided you have current as well) As has been said, check the voltage at the heater whilst the glow plug is pulling power, typically on a DW this will begin around five seconds after switch on and continue for around 15 - 20 seconds, unlike the air heaters it will be a continual draw rather than a pulsed one.

Thanks David. Yes that why I want to rig in a radiator in the saloon so I could run the webasto without using the draw from the separate fan units which is remarkably high actually. Not good for a cruising boat not on shore power most of the time.

If I rig a radiator I the system and I put it in parallel would it have enough pressure to fill it or would the water find the easiest and lowest route and drive round the air blower units.

 

[David2452]

Thanks David. Yes that why I want to rig in a radiator in the saloon so I could run the webasto without using the draw from the separate fan units which is remarkably high actually. Not good for a cruising boat not on shore power most of the time.

If I rig a radiator I the system and I put it in parallel would it have enough pressure to fill it or would the water find the easiest and lowest route and drive round the air blower units.

Provided you have a header tank higher than everything else and a means of expelling air from the radiators all should be well, best of all of course is discard the header and have a closed pressurised system with a filling loop from the domestic system. If you get issues with poor flow in an area then balance valves will sort that out.

 

[pvb]

I inherited it but I rebuilt the unit from scratch with plenty I advice from David above. It now all works all ok but it would be nice for it to work without any power source like the engine or shore.

But did you "rebuild" the wiring supplying power to it? If the inherited power supply was under-specified, the voltage drop in the cable when you try to start it will result in non-starting and a "low voltage" warning.

 

[Tim Good]

Provided you have a header tank higher than everything else and a means of expelling air from the radiators all should be well, best of all of course is discard the header and have a closed pressurised system with a filling loop from the domestic system. If you get issues with poor flow in an area then balance valves will sort that out.

There is a header tank and next to the unit I do have an outlet from the pressurise fresh water outlet which could be used to link to a filling loop in a pressurised system but st the moment I have a hundred other items to tick off before we leave next April so I have to prioritise where my time goes.

I'll try and rig in a radiator and also a spare webasto water pump to increase circulation. I'll put a switch to that pump so it can run without the webasto heater running. The aim to circulate how water whilst the engine is running using the hot tank as a heater exchanger to the webasto circuit. Will report back if it works ok.