T4 Leisure battery charger oscillation

[Jaco Kruger T4]

Hi everyone, I've got a strange issue with my leisure battery, where the voltage on the leads oscillates between 8 and 14V when connected to mains.
Output from the charger is a steady 14V. So something in the middle must be interfering.
I have a Danfoss compressor unit, and looking at the wiring diagrams, I see there's a 20Amp switch (#13 in the diagram).
I presume it's the black unit between my fingers, that when plugged into the socket in the background closes the switch and causes the problem.
Disconnecting this switch solves the problem, but I don't understand why. Could it be that the output current is less than 20Amps, and it causes the oscillation?

Many thanks for any help

Jaco

 

[Jaco Kruger T4]

I've tested the switch shown in the pic, and it seems to be a 500 Ohm resistor.
Unfortunately my little multi-meter can only measure up to 10 Amps, so I don't want to blow it up by testing the current.

 

[Jaco Kruger T4]

Also, those little wires doesn't seem fit for 20 amps, so it must be some other component.
The mind boggles.

 

[sidepod]

Hi everyone, I've got a strange issue with my leisure battery, where the voltage on the leads oscillates between 8 and 14V when connected to mains.
Output from the charger is a steady 14V. So something in the middle must be interfering.
I have a Danfoss compressor unit, and looking at the wiring diagrams, I see there's a 20Amp switch (#13 in the diagram).
I presume it's the black unit between my fingers, that when plugged into the socket in the background closes the switch and causes the problem.
Disconnecting this switch solves the problem, but I don't understand why. Could it be that the output current is less than 20Amps, and it causes the oscillation?

Many thanks for any help

Jaco

View attachment 111705

View attachment 111706

That’s the temperature sensor.

 

[sidepod]

The switch shown on the wiring scheme is just a general indication that it needs switching.
I real terms that function is taken care of by the control panel above your head in the drivers seat.
When you select ON for the fridge that switch is made. I’m not aware of any relays between the fridge and the control panel so it must be the panel that switches. Simple enough to confirm with a meter.

 

[sidepod]

Actually there may not be a main power switch?
The fridge is just fed via fuse S6. The switching is done via the control panel and fridge control box.

 

[sidepod]

So back to your original problem, the thing you are holding is the battery monitor N162, nothing to do with the fridge.

 

[Jaco Kruger T4]

Thank you. Could the monitor malfunctioning result in voltage fluctuations?

 

[sidepod]

Apologies. N162 is the earth shunt that provides the display with battery voltage.

The thing you’re holding is a temperature sensor that monitors battery compartment temperature.

Let’s start again.
Where are you measuring when you’re seeing a fluctuation in voltage?

 

[Jaco Kruger T4]

No worries
I'm measuring the battery leads (disconnected).
When the sensor is plugged in, voltage on the leads fluctuates between 8 and 14V every second or so.

 

[Jaco Kruger T4]

I've been searching online for the part, but no luck so far.
Do you perhaps have a part number?

 

[sidepod]

This ?

 

[Jaco Kruger T4]

Legend, that seems to be it.
Will see if it solves the problem.

Thanks mate!