High Voltage Alarm

[Seahorse7101]

Motoring across Lyme Bay and high voltage engine battery alarm sounded. Checked Victron and engine start battery reading 15 volts, domestic reading 14.1 volts. Checked batteries and all connections. Started engine and within a minute alarm went off. Used the linking key/switch so as connect domestic battery to engine start. All voltages returned to normal. With engine running both domestic and engine start charging and reading 14.1 volts. Suspect engine start battery but does anyone have any other ideas? Engine is Volvo D2-75 on a 45’ sailboat.

 

[Graham376]

Was the engine battery getting warm and what are the resting voltages when isolated?

 

[Seahorse7101]

No - all batteries were cold, all connections good. Resting voltage was 12.6v. Engine started perfectly when using just the engine battery (before using linking key to domestics)

 

[jwfrary]

Some of the new Volvo's alts have a voltage sense wire.

If the sense wire running to your domestics but the alt outputs going to your start battery then tk your domestic you could easily end up with the voltage loss compensation causing a high voltage on the start bank but an acceptable one on the domestic.

But that's just a theory!

Do you know if it's a diode, FET or voltage sensitive relay on the split charging system and how are they set up?

 

[VicS]

I was also wondering how alternator output was divided between the two battery banks.

Jwfrary's explanation is plausible if a diode splitter , such as VP's charge distribitor, is fitted with the alternator sensing connected to the domestic bank, which being the larger bank and likely to be the more deeply discharged would, I belive, be normal,

 

[Moodysailor]

Agree with the above, if you have a diode splitter this can happen.

 

[Seahorse7101]

Thanks for replies. Just FYI battery charging when connected to shore power is all as normal, so looking like an engine charging issue? I have attached a couple of photos that may help I establishing the likely cause…

 

[Moodysailor]

Thanks for replies. Just FYI battery charging when connected to shore power is all as normal, so looking like an engine charging issue? I have attached a couple of photos that may help I establishing the likely cause…

When on shore power the battery charger will be connected directly to each battery bank and will control the output for each independently, so would not show the issue.

When under engine, the alternator is charging via the diode block (first image). These are effectively electrical one-way valves. For the alternator to know what current/voltage to put out it has to know what the batteries are at (the sense wire - yellow on VP engines). If this sense wire is connected to the domestic bank, it will put out whatever current/voltage is needed to bring that bank up to charge. Due to the "one-way" nature of the diodes, the alternator cannot 'see' the charge level of the start bank, and will keep piling in the voltage until it is happy the domestic bank is charged.

This is why VSR (voltage sensing relays) are better. When the charge voltage is applied the relay connects the two banks together. This has the combined benefit of allowing the domestic and start to acta as one bank, thus equalising voltage across themselves, and the alternator can 'see' the charge on all and will not over or under charge either bank.

In the interim, check that there isn't a bad battery in the domestic bank, but I would advise replacing the double-diode with a VSR.

Best of luck.

 

[Seahorse7101]

Thank you very much

When on shore power the battery charger will be connected directly to each battery bank and will control the output for each independently, so would not show the issue.

When under engine, the alternator is charging via the diode block (first image). These are effectively electrical one-way valves. For the alternator to know what current/voltage to put out it has to know what the batteries are at (the sense wire - yellow on VP engines). If this sense wire is connected to the domestic bank, it will put out whatever current/voltage is needed to bring that bank up to charge. Due to the "one-way" nature of the diodes, the alternator cannot 'see' the charge level of the start bank, and will keep piling in the voltage until it is happy the domestic bank is charged.

This is why VSR (voltage sensing relays) are better. When the charge voltage is applied the relay connects the two banks together. This has the combined benefit of allowing the domestic and start to acta as one bank, thus equalising voltage across themselves, and the alternator can 'see' the charge on all and will not over or under charge either bank.

In the interim, check that there isn't a bad battery in the domestic bank, but I would advise replacing the double-diode with a VSR.

Best of luck.

Thank you very much Moodysailor for taking the time to share your knowledge and suggest the potential issue. I will follow that line of thinking.

 

[Seahorse7101]

Thank you very much

Thank you very much Moodysailor for taking the time to share your knowledge and suggest the potential issue. I will follow that line of thinking.

Quick clarification- you call the first image a diode block even though it is labelled a multi battery isolator, is that correct? Also are you saying that you feel the problem maybe there and is so to replace that unit with a VSR. Is it possible to check outputs on that isolator to further confirm the fault lies there. Thanks

 

[Moodysailor]

Quick clarification- you call the first image a diode block even though it is labelled a multi battery isolator, is that correct? Also are you saying that you feel the problem maybe there and is so to replace that unit with a VSR. Is it possible to check outputs on that isolator to further confirm the fault lies there. Thanks

The nomenclature is just what the manufacturer has decided to call it. It is definitely a diode block, sometimes referred to a s a blocking diode, double-diode, or split charge diode. All very confusing....

There are ways to test the system, but given the fault you describe I wouldn't say it is necessary. A simple test would be to check there is no continuity across the outside posts, and the voltage at either post when the engine is running, and at the batteries. I would definitely try to check that the yellow sense wire on the back of the alternator (which will have been extended, so may be a different colour down the line) has a good connection to the domestic battery bank.

But in short - it is definitely a diode system, and I would recommend to replace it with a VSR.

 

[Seahorse7101]

Thanks again for your patience and help!

 

[Seahorse7101]

The nomenclature is just what the manufacturer has decided to call it. It is definitely a diode block, sometimes referred to a s a blocking diode, double-diode, or split charge diode. All very confusing....

There are ways to test the system, but given the fault you describe I wouldn't say it is necessary. A simple test would be to check there is no continuity across the outside posts, and the voltage at either post when the engine is running, and at the batteries. I would definitely try to check that the yellow sense wire on the back of the alternator (which will have been extended, so may be a different colour down the line) has a good connection to the domestic battery bank.

But in short - it is definitely a diode system, and I would recommend to replace it with a VSR.

Thanks again for your patience and help!

 

[VicS]

Quick clarification- you call the first image a diode block even though it is labelled a multi battery isolator, is that correct? Also are you saying that you feel the problem maybe there and is so to replace that unit with a VSR. Is it possible to check outputs on that isolator to further confirm the fault lies there. Thanks

I agree with Moody sailor that the first image is of a diode splitter. The number of wires connected to it is a little surprising though
I would expect to see the alternator output connected to the centre terminal and the individual battery banks connected to the other two. {See the attached diagram from the installation instructions) Also perhaps the alternator sensing connected to the same terminal as the domestic bank.
The small unfused connections are a little worrying but perhaps there are fuses out of shot.

What is the item in the second picture ?. It looks like another diode splitter but there only appear to be connections to the centre and one end terminals. ???????

 

[jwfrary]

You could also use an ARGOFET which would wire directly in place of your diode block.

These function in the same way as a diode block but without the voltage drop.

 

[Moodysailor]

You could also use an ARGOFET which would wire directly in place of your diode block.

These function in the same way as a diode block but without the voltage drop.

If the issue the OP is experiencing is due to the sense wire being connected to the domestic bank creating an overcharge situation in the start bank, this may not be a wise way to go as the problem will remain.

One advantage of a VSR is that they allow the battery banks to combine and balance themselves during the charge phase.

But it's good to have multiple options.

 

[Seahorse7101]

I agree with Moody sailor that the first image is of a diode splitter. The number of wires connected to it is a little surprising though
I would expect to see the alternator output connected to the centre terminal and the individual battery banks connected to the other two. {See the attached diagram from the installation instructions) Also perhaps the alternator sensing connected to the same terminal as the domestic bank.
The small unfused connections are a little worrying but perhaps there are fuses out of shot.

What is the item in the second picture ?. It looks like another diode splitter but there only appear to be connections to the centre and one end terminals. ???????


View attachment 120062

The split charge diode in the 2nd picture is specifically for the bow thruster battery. Centre post is from alternator… Can’t comment on smaller wires on pic 1, I need to investigate, I assume like that from new. Centre post is from alternator..

 

[Seahorse7101]

You could also use an ARGOFET which would wire directly in place of your diode block.

These function in the same way as a diode block but without the voltage drop.

Thank you for that info

 

[Seahorse7101]

If the issue the OP is experiencing is due to the sense wire being connected to the domestic bank creating an overcharge situation in the start bank, this may not be a wise way to go as the problem will remain.

One advantage of a VSR is that they allow the battery banks to combine and balance themselves during the charge phase.

But it's good to have multiple options.

Hi moodysailor, I am sure you are aware but just in case, the system had appeared to function without issue from 2013 when the boat was built, it was a sudden occurrence that happened which caused the high voltage in the start battery charging when engine running. Is the VSR directly replaceable ie 3 terminals and suitable for just swapping cables over. Thank you again

 

[Oily Rag]

But regardless of diodes, VSRs, FETs etc, what was the cause of 15volts being measured at the engine battery?

Something drove the alternator to at least 15volts. Looks more like a wiring or component fault than a poor design of system. If the battery sense wire broke or had a bad connection, would that do the job?