Wiring dilemma

[jimiboy]

I have been asked to assist a friend with a bit of rewiring in a boat which has had the original engine-room wiring stripped out.

The engine is a Volvo MD2B I think, and it is fitted with a Surepower Multibattery isolator Model 702A, two brand new batteries and a 1,2 and BOTH switch, also new. The system is charged by a Bosch 14V - 45A alternator in apparently good nick. The very experienced elderly gent who started the job had done this type of work many times in the past and so it is safe to assume that all these parts are compatible. Unfortunately, he passed away suddenly a few weeks ago, hence my plea for help.

Can anyone give me any advice on how I should wire this lot together. I am no electrician, but would have a go if I had a diagram or some instructions to follow. If I can get the engine going and charging the batteries, the rest can be done later.

Many thanks,

Jim

 

[VicS]

I would say it is impossible to advise you without knowing what alterations have already been made.

If all the original engine wiring and the harness to the control panel has been ripped out .... ouch.

I've drawn a blank on the Surepower Multibattery isolator Model 702A

I think you should leave this to someone who can assess the situation and who knows what they are up to. If it was your own boat then what you do is down to you but not to frig about with some one elses.

 

[pvb]

[ QUOTE ]
I've drawn a blank on the Surepower Multibattery isolator Model 702A

[/ QUOTE ]It's just an ordinary 70A blocking diode with 2 outputs (and I think the model number is actually 702R).

 

[pvb]

[ QUOTE ]
I am no electrician, but would have a go if I had a diagram or some instructions to follow.

[/ QUOTE ]Like VicS, I reckon your friend would be better off getting a marine electrician to complete this for him. It isn't just a case of connecting wires, it's also a case of selecting correct wire sizes.

 

[jimiboy]

I agree totally that it is a bad idea to mess with someone elses wiring, and I will not attempt the work without the advice I need. The wiring to the control panel, instrumentation etc. is still in place. It is the interconnection between the batteries, alternator, starter motor, 1,2 both switch and multi battery isolator that I want.
I have contacted the European distributor of of the isolator and he has sent me mounting instructions as issued with the new item. Unfortunately, none of the diagrams provided include this 1,2 etc. switch. I am wondering if the isolator is absolutely necessary, as my own system doesn't have one.
Any thoughts on that?

 

[alan]

Have a look at the Adverc web site; this gives some pretty standard wiring diagrams although they include (of course) the Adverc alternator regulator. Just leave out the bits that you don't need and you will be left with a pretty standard wiring circuit.

Alan.

 

[PuffTheMagicDragon]

If you can identify the output of the alternator, this goes to the central stud of the diode splitter. Two wires then go from the other studs, one to each '+' terminal of the batteries and serve for charging. Thick cables go from these '+' terminals to the outer studs of the 1-2-both-off switch. The central stud on the switch feeds your system via a wire of thickness appropriate for your loads. A thick cable also goes from this stud to the starter motor. Another thick cable joins the '-' terminals of the batteries to each other and to earth (engine block).

This way, you can start the engine on either battery and you can still use whichever one you want to run your lights, etc. The main advantage is that you cause no harm by turning the ignition key accidentally to 'off' because the alternator is permanently linked to the batteries.

The disadvantage is a slight loss in the voltage that is going to the batteries.

I have lived with this system for many years. HOWEVER, if you have any doubts or are not convinced, then get a good electrician to have a look.

Good luck.

 

[VicS]

The simplest solution to get things going is to connect the main cable between engine and battery to the 1/2/both/off switch common terminal and the individual batteries to the other two terminals. Then you'll have a system in which you can select either battery as the one in service but you'll only be charging the selected one.

To bring the diode splitter, as we now know it to be, into use you will have to separate the alternator output from the main cable and connect it it directly to the common terminal of the diode splitter with the other two terminals connected to the batteries.

However that raises the issue of sensing for the alternator. It really ought to be battery sensed to overcome the volts drop on the splitter.

Also if you wish to make one battery a dedicated engine battery and the other a dedicated domestics battery more segregation of the wiring may be necessary together with some changes to the switching.

You find some basic info at http://www.tb-training.co.uk/cover.html but you would be well advised to study a good book such as Nigel Calder's

 

[jimiboy]

Many thanks for your hlpful comments gents. Particularly to VicS for that website. It is a laymans goldmine !
I can at least get the motor going.
Jim