WAECO charger blowing fuses - need advice on replacing NTC Thermistor

Thread Starter


Joined Dec 13, 2020
Hi all

Wondering if anyone can help with this. Background:

WAECO charger on my boat approx 10 yrs old blew fuse while charging one night. Tried replacing fuse and it blew right away with no battery attached to charger and seemed to also blow something else internally. Opened it up to see that I have the following damage visible:

1. NTC Thermistor - chunk of it is missing
2. Burned PCB area at the base/pins of 2 x MOSFET

All of this is downstream of a Bridge Rectifier (first one after the 230V transformer) and I have read on some forums that this can often be a culprit (internal short). I am considering to replace all 4 components as they are cheap and its worth a shot instead of the 400-500 dollars for a new unit.

One issue I have is that the NTC thermistor has markings on it that I cannot decipher so I dont know what spec it is. It is stamped with 005 06.
At 16 degrees C I read 7 ohms across the pins, but due to damage I dont think I should rely on that reading.

Any one have any idea what Ohms and Amps spec I should have on this Thermistor? For info its green in colour and looks like ceramic insulated approx 10 mm in diameter (disc shaped with two prongs).

The charger spec is as follows:

230V in for 12V system in boat
Max charge current 25A
Max battery capacity 300ah
Fuse for supply power 4A

Thanks in advance for any help


Thread Starter


Joined Dec 13, 2020
Hi there - thank you for your reply

I´ve taken a couple of photos - please see below.

The items I can see that are visibly damages are circled. There are 2 x MOSFET units to the right - one is burned at the pins at the base and the other there is burning under the board at the pins.

Note that all of the components that are visible damaged are downstream of the bridge rectifier (just to the right of the green NTC thermistor). I read on a couple of forums that folks have issues with these shorting and causing this kind of damage. Its not visibly damaged though and I do not know how to identify issues with this unit (across the pins with a multimeter for example).

I was going to replace all damaged or suspect items (NTC thermistor, Bridge Rectifier and 2 x MOSFETs) its just the NTC Thermistor spec that puzzles me. If you can help with that I´d be extremely grateful.




Thread Starter


Joined Dec 13, 2020
You are quite right - good spot! I didn't notice that before. They have leaked onto the board at their base.

Any idea what has happened here to cause these multiple failures? And what component could be the source of the problem?

Given this latest discovery I´m thinking this unit is a write-off and that I will need to cough up and buy a new one.. shame as I was looking forward to the repair and a chance of more years of service of this one.