What is this in my engine bay?

[Swenns Dad]

Maybe it’s a smoothing/spike/noise filter? Boat has a JRC RADAR so maybe it’s a filter??

 

[john_morris_uk]

The black domed thing is a transformer. I've worked with identical ones in different circumstances.

This means that it's a home made inverter or similar. Does the alternator have a separate connection through to the battery or does the main feed from the alternator to the batteries only go 'through' this unit?

 

[Swenns Dad]

Hi there. There is only one output from the unit, being a large gauge brown cable. I’m going to trace that to see if goes direct to battery.

 

[Swenns Dad]

The black domed thing is a transformer. I've worked with identical ones in different circumstances.

This means that it's a home made inverter or similar. Does the alternator have a separate connection through to the battery or does the main feed from the alternator to the batteries only go 'through' this unit?

Just to confirm, only source out of alternator is through the unit (large positive cable).

 

[Rich T]

Maybe it’s a smoothing/spike/noise filter? Boat has a JRC RADAR so maybe it’s a filter??

Do not think it’s a regulator, not enough connections. No connection to alternator field ?
Again with a negative connection cannot see it being a diode splitter. And where is the connection to the second battery?
If anything, and it’s a big if, it might be some sort of filter/ suppression unit. The “transformer” might be an inductor (choke), although at the frequencies that are normally needed to be suppressed it would be a lot smaller. However the connection, in, out - and ground would make sense.
First post so please forgive if this arrives a little late !
Richard

 

[Swenns Dad]

Do not think it’s a regulator, not enough connections. No connection to alternator field ?
Again with a negative connection cannot see it being a diode splitter. And where is the connection to the second battery?
If anything, and it’s a big if, it might be some sort of filter/ suppression unit. The “transformer” might be an inductor (choke), although at the frequencies that are normally needed to be suppressed it would be a lot smaller. However the connection, in, out - and ground would make sense.
First post so please forgive if this arrives a little late !
Richard

I agree. It must be a filter, suppressor. Probably removes any AC on the DC line. As you say, if it was a regulator there should reasonably be another line feeding back to regulator.

 

[john_morris_uk]

Do not think it’s a regulator, not enough connections. No connection to alternator field ?
Again with a negative connection cannot see it being a diode splitter. And where is the connection to the second battery?
If anything, and it’s a big if, it might be some sort of filter/ suppression unit. The “transformer” might be an inductor (choke), although at the frequencies that are normally needed to be suppressed it would be a lot smaller. However the connection, in, out - and ground would make sense.
First post so please forgive if this arrives a little late !
Richard

I thought there was a slim possibility of it being a choke as well, but it would be so unusual to have a choke of that size that I discounted it and chose to treat that possibility as vanishingly small.

If it's a filter, then the DC resistance between the input and the output should be very very low. It can easily be checked with a multimeter.

Alternatively, just remove the device from the charging circuit and see if the alternator starts to work properly.

Another test would be to ensure that there is full battery volts appearing on the main output of the alternator when the engine is stopped. With the batteries 'on' the +Ve terminal on the alternator should be a direct connection straight through to the battery positive.

 

[Rich T]

I thought there was a slim possibility of it being a choke as well, but it would be so unusual to have a choke of that size that I discounted it and chose to treat that possibility as vanishingly small.

If it's a filter, then the DC resistance between the input and the output should be very very low. It can easily be checked with a multimeter.

Alternatively, just remove the device from the charging circuit and see if the alternator starts to work properly.

Another test would be to ensure that there is full battery volts appearing on the main output of the alternator when the engine is stopped. With the batteries 'on' the +Ve terminal on the alternator should be a direct connection straight through to the battery positive.

+1, that’s certainly what I would do. The “choke” may be that size because of the heavy windings used to support the expected high through current.

 

[Swenns Dad]

Just incase.... that was a noise filter... I have the specs now, should anyone ever need it

 

[peteK]

It may be some sort of diode to stop the battery discharging through the alternator when engine at rest,may of been used with a previous engine or dynamo ,use multimeter to check.

 

[STILL AFLOAT]

Could it be an old style galvanic isolator ?

A galvanic isolator is a device used to block low voltage DC currents coming on board your boat on the shore power ground wire. These currents could cause corrosion to your underwater metals; through hulls, propeller, shaft etc.

The bit that looks as if its part of an inverter, could in reality , be a huge heat sink.
Good Luck with your quest & please let us know what you find out.

 

[LittleSister]

Good Luck with your quest & please let us know what you find out.

I think he did, earlier today at post number 29.

 

[Swenns Dad]

Yes, it’s a Noise Filter... assume fitted when RADAR was fitted- have the spec sheet now, so mystery solved.