This charging system wiring seems odd

Sans Bateau

Sans Bateau

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As a result of unexpected flat batteries the other weekend I spent the day on Sat investigating why. I believe I found the reason but during my investigation found something strange. The power from the alternator went straight to the house bank with then a thinish wire to the starting bank for charging. There was no split relay, no way to stop domestics and nav stuff running down the starting battery. Having checked the wiring diagram in the boat details at home, this is how it was made!

So what I have done is to to reroute the alternator cable to the starting battery and I am going to install a DVSR between the starter battery and house.

I do question myself though changing what the manufacture did 20 years ago, but it does seem a daft setup they installed. Am I right in what I am doing?
 
I would say you are absolutely right, to directly connect the house batts and start batts in the way you describe seems daft to me
 
Spot on IMHO. It was, and still is, regarded as OK to wire the House and starter batteries across each other, but there is a real risk of discharging the whole lot - as you discovered! Also if the house battery is higher capacity and lower charge level, it can drain down the starter battery until they reach equilibrium. The 'correct' re-wire is exactly what you are doing: Ensure the starter battery gets priority, either with some form of VSR to cut off the house battery until the engine is running, a splitter diode (which simply gives equal charge to both batteries) or by a simple relay that only connects the house battery to the charging circuit when the engine is switched on. The third option is crude, as if the house battery is low, it will add a load the starter battery just at the critical moment, but at least it avoids the dead starter battery.

But in my book just connecting the two banks of batteries across each other is a big no-no if you want to be sure of being able to start up reliably. I suppose twenty years ago there was nothing like the level of current demand on the house batteries that modern electronics and gizmos give nowadays, and it didnt matter so much. You will find the same set-up in caravans and motorhomes of 20 years ago, but not nowadays.
 
oldharry said:
But in my book just connecting the two banks of batteries across each other is a big no-no
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Surely it's impossible to have two banks of batteries simply connected together like this? What you're then looking at is one bank of batteries...

Pete
 
When you buy your voltage sensing relay don't be tempted by the cheap, allegedly 180 amp ones on ebay and elsewhere. Durite 140 amp ones appear to be good.
Merlin who make the Smart Gauge battery monitor and the Smart Bank controller do not sell their relay separately but this page http://www.smartgauge.co.uk/more_relay.html shows the comparison between theirs and a so called 180 amp relay.
 
Norman_E said:
Merlin who make the Smart Gauge battery monitor and the Smart Bank controller do not sell their relay separately
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They don't, but you can buy it from someone else instead. It's not a Merlin product, it's a standard Albright contactor. I believe the one they include with the Smartbank is an SW180.

Pete
 
prv said:
They don't, but you can buy it from someone else instead. It's not a Merlin product, it's a standard Albright contactor. I believe the one they include with the Smartbank is an SW180.

Pete
Click to expand...

That's right, its a contactor, and in the Merlin setup the Smartbank controls it. I don't think it works as a VSR on its own, but is just a plain relay powered up or released by the Smartbank.
 
The arrangement of battery connections definitely seems strange. I presume you are sure of the connections you founbd and also that it is what was intended in the diagram.
If so then as said you simply have 2 batteries wired as one. The thin wire interestingly might get hot or even melt if the starter battery was a bit tired as the thin wore would carry a lot of the start current then. The resistance would jormally limit the amount of start current taken from the domestic battery.
Given that the boat would have had many replacement batteries the wiring may have been changed to the crazy arrangement you found. What was common back then was the 1,2,both/off switch and I wonder if one was fitted then removed.
Anyway the VSR will be a very good way for you to go. Get one which can carry start current from the domestic battery or fit an emergency switch or carry a jumper lead.
good luck olewill
 
When I wired my boat I installed a one,two,both and off switch and isolators for both batteries.The system works perfectly and there are no electronics to go wrong.I only use the both position when I'm running the engine.As soon as I switch it off I turn the switch to the house battery.
 
So whilst slightly off thread- how can I tell on my boat that the starter battery is getting the initial charge then the house battery is getting the charge
Other than running the house batteries to zero then seeing if the engine starts
I am worried that I might flatten the start battery by mistake if I use too much electric on the house battery
 
Daydream believer said:
To be honest i do not have a clue i just see loads of wires all over the boat. For all I know the fairies come out when i am asleep & sort it
That is why i was asking how do i find out
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In that case it would be a good idea to find out, at least for the "heavy" battery wiring, what is wired to where. Follow each of the wires and draw a diagram and all should become clear, or post it here and people can explain it for you. A photo of any mysterious boxes with multiple wires going in and out would be very useful.

Pete
 
prv said:
In that case it would be a good idea to find out, at least for the "heavy" battery wiring, what is wired to where. Follow each of the wires and draw a diagram and all should become clear, or post it here and people can explain it for you. A photo of any mysterious boxes with multiple wires going in and out would be very useful.

Pete
Click to expand...

Thanks
A winter project me thinks

Because the wiring is so complex I carry a set of long HD jump leads
This allows me to hook 2 batteries together if I get a problem or take leads from the battery to starter motor & earth & bye pass the whole lot to get the engine going
have done it once so far in 11 years but fortunately got me out of trouble
I even have a DIY loom going from the batteries with a 60 amp fuse ( drawn until needed) which terminates near the VHF & GPS so I can bye pass the lot in an emergency & get the VHF & GPS working
As for the wiring to the switch panel on the Volvo --- no chance !!!!
 
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Daydream believer said:
As for the wiring to the switch panel on the Volvo --- no chance !!!!
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Yeah, no need to dissect the engine loom for this purpose. Just draw the engine as a lump with the negative wire to it, the positive to the starter motor, and possibly a separate positive from the alternator to the vicinity of the batteries.

Pete
 
The way I did it was with a VSR cluster. The battery bank system is very straight forward with just a few large wires. Then you take a red and a black wire from your 'house' to a busbar which all the little fairy wires connect all the magic electrical stuff to. This way you have the basic, important engine starting/charging circuit and a seperate crows nest of little wires to bits and bobs. The VSR cluster has an on switch for house, one for start and an emergency parallell to connect the two if your engine is not starting easy. Works very well and easy to faultfind. Also no need to remember to flick switches as with a 1/2/both/off switch.
 
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