Electrical numpty seeks wiring diagram

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Present set-up is two leisure batts on a 1-2-both switch with one kept exclusively for engine starting.

I intend to buy a dedicated engine start battery (small car batt.) and wire my two existing 110AH leisure batts in parallell.

Anyone got a simple wiring diagram?

- W
 
In essence you already have the circuit in place. I think all you need to do is reconnect the leisure battery you are using for engine starting in parallel with the other leisure battery, pos to pos and neg to neg. You can then connect your engine start battery to your engine start circuit.
 
as above but ideally make the negative connection to one battery of the domestic bank and the positive to the other. It helps to even up the charging and discharging between the two

scan0138.jpg
 
Except get rid of the 1-2-both-off switch (which is an accident waiting to happen) and get separate isolators for each bank. Connect the starter battery through the isolator to the starter circuitry and connect the domestic bank through the isolator to the domestic circuits.

You'll also need a third isolator if you want to connect the domestic batteries to start the engine (note this is not linking the batteries together as when the starter battery is duff enough for you to need the domestics to start the engine you don't want it connected up).

Ideally in the future, set up the battery charging circuits to avoid the switches, then it'll all be virtually crew-proof.
 
Not sure

VicS said:
as above but ideally make the negative connection to one battery of the domestic bank and the positive to the other. It helps to even up the charging and discharging between the two

scan0138.jpg
Click to expand...

Slightly worried about the two batteries in parallel without any isolation as there is a chance that one battery may have a slightly higher voltage (age, duff cell et) causing the other battery to be drained.

Also no wiring protection in the event of an internal short. I would fit fuses on each battery to cover the current rating of the wire. Considering that a 12 volt battery can deliver 500, amps this could lead to a fire hazard if you have only 2mm2 wire.
 
Jcorstorphine said:
Slightly worried about the two batteries in parallel without any isolation as there is a chance that one battery may have a slightly higher voltage (age, duff cell et) causing the other battery to be drained.

Also no wiring protection in the event of an internal short. I would fit fuses on each battery to cover the current rating of the wire. Considering that a 12 volt battery can deliver 500, amps this could lead to a fire hazard if you have only 2mm2 wire.
Click to expand...

Better do another diagram incorporating those suggestions.... be my guest!
 
VicS said:
Better do another diagram incorporating those suggestions.... be my guest!
Click to expand...

Would love to but as you know, I always get tied in knots with photobucket, posting pics etc. The guy just needs to fit an online fuse between the two positive connections rated to his max demand and one to the 2 way switch but the fuse should also not exceed the safe rating of the wire.

See here for ratings and work to the lowest temp rating.

http://www.energy-solutions.co.uk/cable_conductor.html

I also think there is a need for a blocking diode between the two batteries to stop self discharge but cant get my head round it at the moment due to "red wine haze".
 
dt4134 said:
Except get rid of the 1-2-both-off switch (which is an accident waiting to happen) and get separate isolators for each bank . . .

(snipped)

Ideally in the future, set up the battery charging circuits to avoid the switches, then it'll all be virtually crew-proof.
Click to expand...

We've been using the 1-both-2-off switch successfully for ten years now so I;m not worried about that.

The budget is limited, the space is limited and Vic's solution above is pretty much what I was looking for. I can see the point in having switches to siolatre each battery in the domestic bank separately, but space is limited - I don't think there is any way I can poke much more heavy wiring in there.

- W
 
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Jcorstorphine said:
Slightly worried about the two batteries in parallel without any isolation as there is a chance that one battery may have a slightly higher voltage (age, duff cell et) causing the other battery to be drained.

Also no wiring protection in the event of an internal short. I would fit fuses on each battery to cover the current rating of the wire. Considering that a 12 volt battery can deliver 500, amps this could lead to a fire hazard if you have only 2mm2 wire.
Click to expand...

I've never seen fuses in the wires making up a bank from more than one battery. Elsewhere certainly but never in these wires which are often around 50mm2 CSA so fuse size in hundreds of Amps. Were you actually talking about a fuse outside the battery box?

Good guide to connecting batteries here wrt wiring. http://www.smartgauge.co.uk/batt_con.html
 
Mistroma said:
Good guide to connecting batteries here wrt wiring. http://www.smartgauge.co.uk/batt_con.html
Click to expand...

Thanks, that's interesting - same as in Vic's diagram (taking -ve and +ve feeds from different batteries) - thoujh it is obviously easier and less critical with only two.

Re. a 'dud' battery dragging the other one down - how much difference between the batteries does there have to be before this is a real problem?

- W
 
Jcorstorphine said:
I also think there is a need for a blocking diode between the two batteries to stop self discharge but cant get my head round it at the moment due to "red wine haze".
Click to expand...

Which way are you putting the diode, one will stop charge, the other will stop discharge, while limiting charge to one battery and discharging one more than the other. You could fit a by-pass switch :)

Battery interlink cables are normally 25 - 50 sq mm, so resistance is very close to zero, thus in normal use the volt drop is very close to zero, So the only difference you see in voltage is due to normal battery variation, and could be either battery high. But as the voltage is generated by the battery, the voltage you see suits that batteries requirement, unless there is very high charge or discharge rates, in which case cable volt drop becomes an issue.

If the OP is happy with 1,2,both fine, it's his boat.

Brian
 
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Batteries in paralell

I would think it worth while to keep the 1,2,both switch for the domestic batteries. Eventually one will die first and this can then easily be isolated and dealt with if you can easily separate the 2 domestic batteries. Yet normal operation would be on both. Separate battery fuses are not often seen.
As said wire up the new engine battery to just the engine circuits including charging via an isolation switch.
Then fit a VSR between engine and domestic batteries (1,2,both switch)
Either get a VSR with paralelling capability for emergency engine starting off the domestic batteries or fit another high current switch between the 2 batteries hidden and or guarded.
Or fit one high current switch between the batteries for emergency start or for normal charging. (not the best but cheapest).
A wiring diagram might seem good but it is all logical if you understand what you are doing and why. (and you should) good luck olewill
 
William_H said:
A wiring diagram might seem good but it is all logical if you understand what you are doing and why. (and you should) good luck olewill
Click to expand...

If I knew what I was doing I wouldn't have asked . . .

Thanks to Vic, am going to KISS as per the existing set-up with the 1-2-both switch isolating the start battery or the domestic bank.

- W
 
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