Author Topic: Dynamo mistery  (Read 1021 times)

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Offline Marien

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Dynamo mistery
« on: 23 May, 2020, 22:23:37 »
This weekend I noticed a problem with the charging from the dynamo’s. Our boat has 2 dynamo’s which are paralleled with 2 Volvo Penta Diode blocks. 1 dynamo voltage raised to over 17V, boiling the start battery. The other appears to be dead. I’m not sure but I think the one that looks dead is an already long existing problem as some studying revealed a charge light which I haven’t lit before on my dash. So most likely since before we purchased her a year ago that dynamo isn’t doing anything.

I opened op a lot flooring and furniture and found the 2 diode blocks. Measured them and the one connected to the dynamo with the high voltage level is dead. As the other isn’t doing anything I swapped the diode blocks and now that dynamo is working fine again.

In the meantime I found a couple of serious errors in the Contest of which I’m certain this is not modified by the previous owner. The drawing shows 2 charge lines from the Victron charger; well there is only 1 charge line. My start battery is only charged by the engine. Another error is the fact that even when both main switches are off, I can still start the engine. Finally I found that the bow thruster is connected to the motor after the main switch. Then the bow thruster motor can act as start battery. Strange.
The last error I found was within the wiring from behind the diode block. It’s a minor error when switches are closed but I still figuring out what the impact is.

Now my questions. Are there other Contests with 2 dynamo’s paralleled by means of diode blocks. How then do the dynamo’s get there pre magnetize voltage. There is no voltage on the diodes as the output are sperred in that direction. All the Volvo manuals show different setup, some also including diode blocks, but none as our setup using them to paralel the dynamo’s.

I have no clue how the functioning dynamo now gets his pre charge voltage but that one seams to work fine now. The other one but short circuiting the faulty diode block (simply connecting the in with 1 of the outputs, I now get the charge light ON and voltage on the B1. The light remains on and the charge current is really low. So I think this dynamo is due for service.

For replacing the diode block(s) I’m considering to get them out and install an Victron Argo FET charge distributor. But again I haven’t seen an example drawing whereby the dynamo’s are paralleled.

Lucky me, the dynamo that now appears to be working fine, is the one on the back side of the motor. No I idea how Contest things that side of the enige can be reached for servicing. The one opening I have could also have been made bigger to better services the front of the motor. This is not what you should expect with a Contest.

Nevertheless, does this story sounds familiar and/or is there somebody with some advise. It is more then welcome.