Help understanding boat electrics - 1991 Hunter Horizon 27

[BenMurphy]

I've just bought a 1991 Hunter Horizon 27, and I'm struggling to understand the battery set-up slightly. There are two batteries, but both feed into a very tight bundle of cables that run through the cockpit floor and up past the engine compartment, so it's impossible to follow the circuits without taking the whole bundle apart, which is going to take more effort that I'm willing to put in at the moment. Also I'm not confident about putting all back together competently!

Basically there are two batteries, that I assume to be the domestic and engine batteries. There are two separate isolators. The left isolator operates the domestics, and is pretty simple - if it's on they work, if it's off they don't.

The right isolator operates the engine starter battery (I think), but the engine will only start if both the isolators are set to on i.e. if the engine isolator is on but the domestic is off, the engine won't start. See my dodgy sketch which helps explain.

My assumptions are thus these - please affirm or challenge them!

- This suggests that the circuits to both batteries are running parallel
- If so, the boat will start via the engine battery if the domestic battery is flat, but both circuits would still need to be open
- This suggests that the alternator will charge BOTH batteries if both circuits are open when the engine is running

I believe I can test the last assumption using a multimeter when the engine is running and checking if both batteries are registering > 13V. Is there any way I can confirm the other assumptions without picking apart the big cable mess?

I'm pretty new to this so please help if I've completely misinterpreted the whole thing!

 

[anoccasionalyachtsman]

At first sight that looks unusual. A voltmeter will help enormously, but in the meantime - is there any clicking from the engine area, however faint in either of the one on/one off combinations?

The reason I ask is that I'm wondering if both batteries are so low that they can't manage the engine alone, whereas both combined is enough, and the clicking I mention would confirm that.

 

[PaulRainbow]

You need to identify which cables go where, otherwise it's impossible to tell what the problem is, but it looks to me as if something is incorrectly wired. You can use a multimeter to work out which battery cable is which and where it goes. Write it all down and note all connections at the switches, note anything else, such as split charge relay or diodes, if present.

 

[BenMurphy]

At first sight that looks unusual. A voltmeter will help enormously, but in the meantime - is there any clicking from the engine area, however faint in either of the one on/one off combinations?

The reason I ask is that I'm wondering if both batteries are so low that they can't manage the engine alone, whereas both combined is enough, and the clicking I mention would confirm that.

No no clicking at all. The domestics work fine and the engine starts straight away with both isolators on, so it seems unlikely that the batteries are flat. I'll double check with multimeter next time I'm there for sure.

 

[Baggywrinkle]

There's no easy way out of this one I'm afraid ... you need to create a circuit diagram to understand what exactly is going on.

The boat is almost 30 years old so the chances of everything being wired or functioning as original are almost nil and you have no idea what is lurking in the "bundle" of cables unless you can trace them all physically from connection to connection.

Sounds like your first adventure with your new boat is going to be sorting out the electrickery - just bite the bullet and start on the learning curve while it is not sailing season. Afterwards, you will know your boat electrics inside out and you will be much more confident - but most of all, you will not be forced to trace and fix the connections out at sea at the most inconvenient moment possible.

Having an accurate wiring diagram to refer to makes fault finding and quick fixes, bypasses etc. so much easier when the preverbial hits the fan - which it inevitably will do at some point in your future - so your time now will not be wasted.

 

[rogerthebodger]

What it looks like to me is that the engine switch powers the engine starter motor but the engine starter circuit is powered from the domestic battery.

It's not really a problem as such but can be confusing. It would only be an issue if the domestic battery was totally flat.

All you need to do is find the wire that goes from the domestic battery to the starter switch and change it to the engine start battery.

I know Paul likes to have a bridging switch between the engine and domestic battery which is a good idea just to allow you to start the engine from the domestic battery if ever the engine battery is totally flat.

 

[VicS]

I've just bought a 1991 Hunter Horizon 27, and I'm struggling to understand the battery set-up slightly. There are two batteries, but both feed into a very tight bundle of cables that run through the cockpit floor and up past the engine compartment, so it's impossible to follow the circuits without taking the whole bundle apart, which is going to take more effort that I'm willing to put in at the moment. Also I'm not confident about putting all back together competently!

Basically there are two batteries, that I assume to be the domestic and engine batteries. There are two separate isolators. The left isolator operates the domestics, and is pretty simple - if it's on they work, if it's off they don't.

The right isolator operates the engine starter battery (I think), but the engine will only start if both the isolators are set to on i.e. if the engine isolator is on but the domestic is off, the engine won't start. See my dodgy sketch which helps explain.

My assumptions are thus these - please affirm or challenge them!

- This suggests that the circuits to both batteries are running parallel
- If so, the boat will start via the engine battery if the domestic battery is flat, but both circuits would still need to be open
- This suggests that the alternator will charge BOTH batteries if both circuits are open when the engine is running

I believe I can test the last assumption using a multimeter when the engine is running and checking if both batteries are registering > 13V. Is there any way I can confirm the other assumptions without picking apart the big cable mess?

I'm pretty new to this so please help if I've completely misinterpreted the whole thing!

One possible explanation is that the batteries are connected in parallel. That one isolator, the left hand one, is the master and that the other is fed from it
Pure speculation.

As Baggy Wrinkle says you need to trace the wiring. If you have a meter with a continuity buzzer that may be useful
but beware of using a digital voltmeter. They take so little current that they will often give a reading when you'd expect them not to. Guaranteed to make a fool of you sooner or later. It is better to use a test lamp

BTW switches are ON when they are closed and OFF when they are open.

 

[BenMurphy]

One possible explanation is that the batteries are connected in parallel. That one isolator, the left hand one, is the master and that the other is fed from it
Pure speculation.

As Baggy Wrinkle says you need to trace the wiring. If you have a meter with a continuity buzzer that may be useful
but beware of using a digital voltmeter. They take so little current that they will often give a reading when you'd expect them not to. Guaranteed to make a fool of you sooner or later. It is better to use a test lamp

BTW switches are ON when they are closed and OFF when they are open.

View attachment 83610

Thanks VicS. I did know that in the deepest recesses of my brain but clearly I was using the wrong terminology!

I suspect that they are in parallel, as you say. Looks like I'll need to bite the bullet and trace the wiring!

 

[Alex_Blackwood]

Thanks VicS. I did know that in the deepest recesses of my brain but clearly I was using the wrong terminology!

I suspect that they are in parallel, as you say. Looks like I'll need to bite the bullet and trace the wiring!

I think you mean in Series not Parallel. In Parallel either switch would give you power.

 

[VicS]

I think you mean in Series not Parallel. In Parallel either switch would give you power.

Well I meant in parallel ....................I was thinking the switches could be wired like this *. It is purely a guess but would explain Ben Murphy's observations.

What series arrangement are you thinking of and why would they be in series

*

 

[PaulRainbow]

Well I meant in parallel ....................I was thinking the switches could be wired like this *. It is purely a guess but would explain Ben Murphy's observations.

What series arrangement are you thinking of and why would they be in series

*

The batteries are in parallel, but the switching for the engine is in series.

 

[RupertW]

Well I meant in parallel ....................I was thinking the switches could be wired like this *. It is purely a guess but would explain Ben Murphy's observations.

What series arrangement are you thinking of and why would they be in series

*

I think you are right, but what a pointless arrangement, and worst of all ensures there is no way to stop domestic use flattening the batteries needed to start the engine.

 

[tjbrace]

Could it be that the starter motor solenoid is on the domestic supply and the starter motor power is on the engine supply.

 

[anoccasionalyachtsman]

Could it be that the starter motor solenoid is on the domestic supply and the starter motor power is on the engine supply.

Don't think so - the OP reported that no clicking is to be heard with either 'off'.

 

[status]

Could try disconnecting one of the terminals of the engine battery and see what happens?

Edit. Not with the engine running but see if it still kicks over.

 

[halcyon]

They started with two battery banks, service and engine each with isolator, changed to two battery service bank, but kept the engine isolator. May be it had blocking diodes or VSR that failed, and this is a owner bodge to to get round the fault.

Brian

 

[Alex_Blackwood]

Well I meant in parallel ....................I was thinking the switches could be wired like this *. It is purely a guess but would explain Ben Murphy's observations.

What series arrangement are you thinking of and why would they be in series

*

Yes exactly like that. Perhaps the engine switch has been connected to the wrong side of the domestic one i.e. It should be on the feed side of the domestic switch. Other than that Someone may have thought it a good idea.

 

[ghostlymoron]

One switch in each leg would make more sense to me

 

[Dunx]

The Hunter Owners Association have a number of wiring diagrams available in the members area if that helps. I had a 30 and they were a good resource for most issues

 

[Humblebee]

https://www.google.com/url?sa=t&rct...p/0713667036&usg=AOvVaw0bpfEgYqNm86dZPSgv8wk7

I'm not qualified to add further comment to the above but may I suggest buying yourself a book on boat electrics? The 12 volt bible, link above, is in my view the best. A little light reading while the nights are still dark!