Tacho fails when batteries charged.

[MoominPapa]

Melaleuca has an electronic tachometer, driven from the W terminal on the alternator. The tacho is made by VDO and the alternator is a bog-standard A127.

 

The tacho has started to misbehave when the batteries are charged and the charge-current reduces to a low level. The reading becomes erratic and then falls to zero. I can see why, in theory, this might happen, but it never used to. The alternator was stripped, cleaned and checked over the winter, and this behaviour is since that was done, but that may be coincidence. There's an ammeter on the alternator output, so I can be sure it's working as usual. There's an Adverc controller attached; taking that out of circuit doesn't help.

 

Any suggestions for things to check/fix or ways to overcome the problem.

 

 

MP.

 

 

 

 

 

 

[Guest]

Melaleuca has an electronic tachometer, driven from the W terminal on the alternator. The tacho is made by VDO and the alternator is a bog-standard A127.

 

The tacho has started to misbehave when the batteries are charged and the charge-current reduces to a low level. The reading becomes erratic and then falls to zero. I can see why, in theory, this might happen, but it never used to. The alternator was stripped, cleaned and checked over the winter, and this behaviour is since that was done, but that may be coincidence. There's an ammeter on the alternator output, so I can be sure it's working as usual. There's an Adverc controller attached; taking that out of circuit doesn't help.

 

Any suggestions for things to check/fix or ways to overcome the problem.

 

 

MP.

 

Is it recording the engine hours correctly?

[MoominPapa]

Is it recording the engine hours correctly?

Yes, but the engine hour meter is entirely separate, not part of the tacho.

 

MP.

[Guest]

Yes, but the engine hour meter is entirely separate, not part of the tacho.

 

MP.

Ah right. Some are combined my error.

[Timleech]

Have you added solar panels, or any other means of charging?

 

 

Tim

[banj0mel]

I had the engine alternator checked and rebuilt last winter (Isuzu engine) and suffered from an intermittent tacho after refitting, along with the blank 'engine hours' panel (which I had suffered from previously). The tacho would register for a few minutes before dying and then recover after a couple of hours. I linked it to the blank hours display (which would reappear after a warming up period) and put it down to the Isuzu dampness problem. The tacho problem worsened quickly to the extent that it wouldn't work at all.

In the end I unplugged the W terminal and reconnected it several times and, lo and behold, the tacho started working again. It now registers from startup and remains working throughout.

 

Might be worth trying.

Regards,

Mel

 

 

[MoominPapa]

Have you added solar panels, or any other means of charging?

 

 

Tim

I have solar panels, but they're not new. The solar controller float voltage is 13.8, whilst the Adverc is set higher, so the solar stops charging before the alternator when the engine is running.

 

MP.

[Timleech]

I have solar panels, but they're not new. The solar controller float voltage is 13.8, whilst the Adverc is set higher, so the solar stops charging before the alternator when the engine is running.

 

MP.

 

Fair enough. My tacho sometimes cuts out during a prolonged bit of sunshine.

 

Tim

[MoominPapa]

 

Fair enough. My tacho sometimes cuts out during a prolonged bit of sunshine.

 

Tim

Googling, this is not an uncommon problem. I suspect that if it works, it's down to a bit of residual permanent magnetism in the rotor; something that can't be relied on.

 

I'm wondering is a suitable valued resistor, shunting the regulator, to provide minimal excitation at all times would be the solution. SIgh, This is where we need the Nibble character.

 

MP.

[smileypete]

 

 

I'm wondering is a suitable valued resistor, shunting the regulator, to provide minimal excitation at all times would be the solution. SIgh, This is where we need the Nibble character.

 

If there's an ammeter, how much load is needed (try cabin lights) to make the tacho come back on?

 

cheers, Pete.

~smpt~

[banj0mel]

This link - https://amplepower.com/primer/tach/index.html- mentions your type of problem and Smileypete's remedy.

 

Regards,

Mel

[Timleech]

 

 

If there's an ammeter, how much load is needed (try cabin lights) to make the tacho come back on?

 

cheers, Pete.

~smpt~

 

I find that putting on the (electric) kettle for a brew works a treat

[MoominPapa]

I shall experiment with adding electrical loads next time the batteries get sufficiently charged. As liveaboards, this may take some time

 

MP.