Split charge relay

[Moke]

 I have two alternators. One charges the leisure bank, the other, I presume, the starter and the bow thruster batteries. Now the bow thruster has never worked for more than a few days at a time and while I was in the darker recesses of the engine I spotted a “Durite Voltage Sensitive Relay.”  I spotted it because it has a small red glowing light on it. This light is illuminated all the time regardless of whether the engine is running or not. The question is, is this right or is this the reason the bow thruster is unworking?

[Tony Brooks]

It could be. If it is used to charge the bow thruster battery, it probably is not working. Put a voltmeter across the bow thruster with the engine off. Start and rev engine to (say) 1200 RPM and the meter should jump up a bit. Then tell us the non-running andrunning readings.

[Alan de Enfield]

24 minutes ago, Moke said:

Now the bow thruster has never worked for more than a few days at a time

 

Thats your problem - a thruster is only designed to work for a few seconds at a time, NOT minutes, NOT hours and NOT days.

[Jen-in-Wellies]

Where is the bow thruster battery? If at the bow, then there could be a lot of voltage drop, if the wire size is inadequate. What @Tony Brooks said, make some voltage readings with engine running and not.

[Tony Brooks]

2 minutes ago, Jen-in-Wellies said:

Where is the bow thruster battery? If at the bow, then there could be a lot of voltage drop, if the wire size is inadequate. What @Tony Brooks said, make some voltage readings with engine running and not.

 

Also, a photo of the bow thruster battery charging cables with something to scale it from. A clear view of the battery top and clamps will probably do.

 

How many hours do you run a day and at what engine revs?

Edited December 9, 2023 by Tony Brooks

[Moke]

Just so that I’ve got this right in my head. Once the starter battery is full of voltages then the relay diverts them to the ones at the front?

[Jen-in-Wellies]

5 minutes ago, Moke said:

Just so that I’ve got this right in my head. Once the starter battery is full of voltages then the relay diverts them to the ones at the front?

No. It is instantaneous with the engine being on, or other source of extra volts, say from solar panels. Usual way it works is that when the engine starts, the alternator boosts the voltage on one side of the VSR to well over 12.8V and the VSR closes, allowing current to flow across. When the engine turns off, the voltage drops and the VSR opens. What the VSR connects to what, depends on the surrounding wiring.

(VSR = voltage sensitive relay)

[Moke]

Right. All I have to do now is figure out how to make my photo small enough to fit on here. 

[Tracy D'arth]

13 minutes ago, Moke said:

Right. All I have to do now is figure out how to make my photo small enough to fit on here. 

Change the resolution on your phone/camera to a lower one.

[magnetman]

google Online image resizer

[Moke]

Does this work ?

 

[Jen-in-Wellies]

7 minutes ago, Moke said:

Does this work ?

 

It does. You've maybe overdone the resize and somehow introduced a lot of blank space around it. Around 1024 pixels along the longer axis is a good size for forum posts. Where you cropping, as well as resizing the picture? What you've posted shows the negative link between two batteries and a thick cable going off somewhere. OK as far as it goes, but we need to see more and an idea of what we are looking at. House, bow thruster, or engine batts?

[Tony Brooks]

3 minutes ago, Moke said:

Does this work ?

 

 

No, it does not work. The image is far too small, and it does not show any positive terminals. Ignoring the main battery leads, there seems to be a thickish and one not so thick negative leads. If the thick one is a charging lead, it will probably work as long as you charge for long enough. I note that you have not told us about how long you run for each day and at what engine revs.

 

If the relay is to link the bow thruster battery to the engine battery, then on a typical installation, solar charging will not enter into the things.

 

The relay MIGHT be to link the engine and domestic bank, in which case solar will charge both banks, but probably not the bow thruster.

 

How are you getting on with measuring the voltages?

 

Lack of charging would give short bow thruster in times and if that is the problem the batteries have probably suffered from sulphation that dramatically reduces their capacity, so that is two potential causes of short run times.

 

[Moke]

We normally run for around 4 to 5 hours a day when we’re moving. This time of year it’s just run when we need to fill the batteries a little. When I put the first post up I’d had the engine running for a while to charge the domestics but as it’s now all but dark (and very rainy) and we’re planning on moving tomorrow I’ll try the testing tomorrow if that’s ok. 
 

[Tony Brooks]

2 minutes ago, Moke said:

We normally run for around 4 to 5 hours a day when we’re moving. This time of year it’s just run when we need to fill the batteries a little. When I put the first post up I’d had the engine running for a while to charge the domestics but as it’s now all but dark (and very rainy) and we’re planning on moving tomorrow I’ll try the testing tomorrow if that’s ok. 
 

 

Thanks, that is your problem right there. Your bow thruster batteries are lead acid batteries and unless you want to destroy them in a few weeks they need to be kept as fully charged for as much time as possible. If you do not, they will sulphate and suffer reduced or very reduced capacity.

 

Practically, you need to think about at least four hours running an 1200 rpm or a bit more for four hours per day and then an eight to ten hour charge once a week.

 

I guess that you are relatively new to boating because what you write is so typical of new boaters until they learn better.

 

You really need some form of battery monitoring, at a very basic level a decent voltmeter and ammeter. The voltmeter lets you infer the state of charge once the batteries have been off charge for a while, and the ammeter lets you decide when the batteries are as fully charged. That is when the charging current falls to 1 to 2% of battery capacity at 14.2 volts or more. Better still when the current ha stopped falling for the last hour or so.

 

We won't know if the bow thruster batteries are charging until we see the non-running and running values.

[blackrose]

2 hours ago, Moke said:

 I  I spotted a “Durite Voltage Sensitive Relay.”  I spotted it because it has a small red glowing light on it. This light is illuminated all the time regardless of whether the engine is running or not. The question is, is this right or is this the reason the bow thruster is unworking?

 

My VSR splits the charge between the start and BT batteries and the light stays on for a long time after charging has finished.

 

Don't assume your setup is the same as mine, I don't know why anyone would install a VSR between domestics and BT batteries, but they do! It doesn't make any sense to me because your start battery will generally be fully charged quicker than the domestic bank thus more availability of charge for the BT bank. Perhaps that's your problem? I've never run out of BT power, but then I use my BT sparingly. A heavy finger is not your issue is it?

 

Anyway, as part of your investigation try to identify which banks are being split by the VSR. 

____________________

You shouldn't need to do this if your boat's BT charging system is working properly from the alternator, but a workaround is to run a small mains battery charger from your inverter when underway to charge the BT batteries.

 

 

Edited December 9, 2023 by blackrose

[Tony Brooks]

6 minutes ago, blackrose said:

My VSR splits the charge between the start and BT batteries and the light stays on for a long time after charging has finished.

 

Some seem to have a 13.4 cut out voltage, so with a bit of Far Eastern precision manufacturing that could easily be while the surface charge is disipatiing. In that scenario, I don't think I would want a bidirectional VSR because when charging stops, the bow thruster is unlikely to be operated to remove the surface charge. That means it might be possible to slightly discharge the BT batteries into the engine battery.

It might help to study this:

 

 

You might also find the notes on my website useful, you are free to print them out section by section. Web address in my signature, below.