Eberspacher Fuse problem

[Ian_Edwards]

My Eberspacher Hydronic 10 stopped working, the controller worked, but nothing happened at the heater. It was working OK last time I used it, and ran for about 3 hours, and appeared to shut down without a problem.

The heater runs 3 matrix heaters and there's a heat exchanger coil in the calorifier.

On investigation, which isn't easy, the heater is under the cockpit and mounted on the transom, and requires dismantling bits of boat to gain access, I found a melted fuse holder, the centre one of 3 fuse holders and the negative terminal on the main power supply a little scorched (last 2 photos).

I'd recently checked the current drawn using a DC clamp meter with the following results:

I can't see the first few seconds of the start-up sequence, it takes a while to press the button on the controller and get back to the clamp meter.

Battery voltage 14.5v, absorption mode.
initial burn 6amps
winds up to 10 amps as the fan winds up.
jumps to 18.5amps when the 3 matrix heaters kick in.
Dropped back to 13.8amps after about 5 min.
switching aft matrix heater off, drops to 11.5 amps
switching forward matrix heater off drops to about 9 amps, then reduces further as the thermal load reduces and the fan winds down
switching mid matrix heater off drops to 3.5amps.
switching aft matrix on 6.5amps
switching forward matrix on 9 amps
switching mid matrix on 10.75amps, increasing to around 13.5 amps as the heater ramps up.
Battery charger off 12.62volts current 9.4 amps.
Battery charger back on 14.5volts 13.5 amps

That all seemed OK, and the maximum current was within the 25 amp rating of the fuse recommended by Eber.

It's clear that the fuse holder had got very hot before the fuse had blown, as far as I'm aware it was a 25 amp blade fuse and you can see from the photo, that it hadn't blown as, in melted the metal strip, it almost looks like it had fail mechanically at the RHS, I extracted the two half with a pair of pliers.

The Eber had had a full professional overhaul last winter, with new glow pin and screen and a new flame failure sensor. I also got the engineer to replace the 3 fuses and the relay which switches on the matrix heaters.

Why did the fuse holder melt before the fuse blew? it really isn't supposed to happen.
and
Why has just the negative terminal of main 12 volt supply got hot enough to toast the plastic case?
and
Is there anything I can do to stop this happening again?

I'll replace all three fuse holders and the connector, it's cheap and easy to do, but what else?

 

[matthewriches]

9 times of of 10 you’ll see this due to a high resistance joint usually because of corrosion or more often than not, a loose connection.

Put some new connections on or at least nip them up so they are tight. eBay have them as a kit.

Same with fuse holders, the receiving terminals need to be a tight fit.

 

[PaulRainbow]

9 times of of 10 you’ll see this due to a high resistance joint usually because of corrosion or more often than not, a loose connection.

Put some new connections on or at least nip them up so they are tight. eBay have them as a kit.

Same with fuse holders, the receiving terminals need to be a tight fit.

I agree with all of that :encouragement:

 

[Old Bumbulum]

I had a similar problem, the 30A fuse repeatedly blowing. I was told by an experienced marine electrical engineer that the control electronics of the Eber are not advanced and as the battery charge reduces and it's voltage drops the Eber still tries to pull the wattage it needs. Thus as volts on the battery drop the current rises to compensate and eventually pop goes the fuse. He claimed that a blown high-current Eber fuse is almost invariably caused by low battery voltage brought about by the battery running out of charge.

If that's twaddle don't shoot me, it's just what I was told but the rationale fits the circumstances in my case at least.

 

[superheat6k]

I prefer miniature circuit breakers to blade fuses. The ETA 1610 range supplied by RS will directly fit blade fuse holders ...

https://uk.rs-online.com/web/c/?searchTerm=Eta+1610&sra=oss&r=t

Cut back to clean unburnt / non-discoloured cable, and check for any signs of moisture ingress in the enclosure.

 

[Ian_Edwards]

Update:
I cut open the offending connectors, and in both cases it was obvious that the crimps had gone high resistance. Both connectors use 1/4", 6.3mm spade type quick connectors and there was no evidence of excessive heating on either the male or the female part, where they make contact.

The fuse that melted was for the matrix heaters, a 20 amp fuse (according to the manual) and is after the main 25 amp fuse on the input.

Both crimps are original Eberspacher factory made joints, although they are now 12 years old, but they are well protected and in a very dry area of the boat.

From the measurements I made and supplied in the OP, you can see that when I switched off the battery charger and the supply voltage, measured at the bus bar, dropped from 14.5 to 12.62, the current went down, not up, so the loads looks more resistive than inductive, although I can see that if the fan motors stopped spinning, they would have a lower impedance, but that hasn't happened.

I've replaced all the fuse holder, and soldered the crimps, but just at the bare wire ends, in the hope that that will provide a better long term solution.

I'm also thinking of spraying it all with some product to further protect the crimped joints, WD40 or something else?

On reflection, it looks the crimped joints that failed, have corroded over time, even though they were made in factory conditions. The boat has literally 100's of crimped joints, so I guess that I just have to be aware that some will fail.

 

[PaulRainbow]

I'm also thinking of spraying it all with some product to further protect the crimped joints, WD40 or something else?

WD40 would be a waste of time. Vaseline, silicon grease or Contralube would work.

 

[BabaYaga]

you can see from the photo, that it hadn't blown as, in melted the metal strip, it almost looks like it had fail mechanically at the RHS, I extracted the two half with a pair of pliers.

I would not be surprised if it is low quality of the fuse itself, rather than the fuse holder, that is the fundamental fault here.

This photo below shows a 30A blade fuse that has not (yet) blown, just melted the plastic and restricted its own ability to pass current.
It sat in the wiring for a 25A battery charger and the situation caught my attention because the charger wouldn't pass full current when it should. I shifted out the fuse holder after this, but later thought more likely the fuse was to blame.

 

[matthewriches]

One of my driving school trucks had a habit of melting fuses in a similar fashion to this, and indeed, after throwing the box of eBay special fuses away and using some better quality ones, no more melted fuses!

I would not be surprised if it is low quality of the fuse itself, rather than the fuse holder, that is the fundamental fault here.

This photo below shows a 30A blade fuse that has not (yet) blown, just melted the plastic and restricted its own ability to pass current.
It sat in the wiring for a 25A battery charger and the situation caught my attention because the charger wouldn't pass full current when it should. I shifted out the fuse holder after this, but later thought more likely the fuse was to blame.