Charging/Alternator/Battery Question

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mark.adams

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Hi All,

We are new boaters having just bought a 1971 Pilgrim 25. It has a single Volvo Penta and a stern drive. I can't get any 12v electrics on the boat to work without the engine running. It has 2 batteries and some isolator thing by 'sure power'.
Where should i start looking and does anyone know anything about how these isolators work??

Thanks in advance

Mark
 
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That is really interesting, thanks for that. Should add both batteries are good and fully charged. I have 2 key operated battery 'off' switches, one for each, i don't think i have a selector switch anywhere to switch between battery/alternator, i can see the isolator with a heatsink on it bolted to the transom in the engine compartment, i am going to get in there with a multimeter.
The guy i bought it off knew nothing about the electrics so no help there i'm afraid...
I presume it is supposed to be auto switching.
I will be adding shore power with a hookup connector and RCD at some point but as an ex-electrician i am ok with that bit.
Still getting my head around how boats are wired up with the 12v bit...
 
If it is wired as per figure 1 in my link, which I am guessing it is, I really can't see how you would only have power when the engine is running unless the battery is dead. Have you actually checked the voltage on the battery terminals when the engine is off?
 
neale said:
If it is wired as per figure 1 in my link, which I am guessing it is, I really can't see how you would only have power when the engine is running unless the battery is dead. Have you actually checked the voltage on the battery terminals when the engine is off?
Click to expand...

Battery connection to isolator switch faulty, isolator switch faulty, no feed from battery so with the engine running service supply is fed via alternator and blocking diode.

Sure power is a blocking diode to split alternator output to engine and service batteries.

Brian
 
I was running over this in my mind while lying in bed last night and that was the conclusion i came to. Auxiliary battery is definitely good so connection from battery to aux isolator or isolator switch itself will be the first 2 places i look.
Thank you everyone for your contributions, i'm sure that won't be my only cry for help.

M.
 
The charger indicates the battery is fully charged. I do have a MM, going down to the boat wednesday after work to diagnose, i'll start at the battery itself and work towards the isolator switch. Hoping to see 14v thereabouts with no load.
 
mark.adams said:
The charger indicates the battery is fully charged. I do have a MM, going down to the boat wednesday after work to diagnose, i'll start at the battery itself and work towards the isolator switch. Hoping to see 14v thereabouts with no load.
Click to expand...


If it has been on the charger make sure that you run a load for a while to 'equalise' it. They often seem to give a high reading if they have not had a load applied so this could skew your results. From then on it is just a matter of tracing the fault with the MM until you find where the connection is broken.
 
mark.adams said:
Hoping to see 14v thereabouts with no load.
Click to expand...
A fully charged battery at rest and allowed time to "equalise" is 12.8 volts.
12.8 100%
12.2 50%
12.0 30%
11.6 0%

The voltage output at the alternator using a conventional regulator will be no more than 14.2 volts and you will probably lose about 1 volt with splitter diode and wiring losses unless you have compensatory wiring or battery management.
 
Right,
P.D done, it is the battery that is at fault. Took it out of circuit completely and put a MM across it, 2.6v, so that is well and truly goosed.
I doubt it will recover from being that low.
Thanks to everyone for their suggestions especially Tony who was right on the money...
 
Post 2

neale said:
I wonder if your aux/domestic battery is not simply flat/dead. When the engine is running you are effectively running it from the other battery/alternator but when not running and the batteries are disconnected you are left with no power.
Click to expand...

mark.adams said:
Right,
P.D done, it is the battery that is at fault.
Thanks to everyone for their suggestions especially Tony who was right on the money...
Click to expand...

I'm definitely claiming a lakesailor for that one!!!!!!
 
As an aside, do i presume correctly, with the aux battery removed from circuit and engine running, i should see voltage from the charging circuit on the loose terminals thereby indicating that the battery (when replaced) will be charged.
 
mark.adams said:
As an aside, do i presume correctly, with the aux battery removed from circuit and engine running, i should see voltage from the charging circuit on the loose terminals thereby indicating that the battery (when replaced) will be charged.
Click to expand...
Yes ... BUT you need to tape over the positive connector and make abdsolutely sure it cant accidentally short to any other metalwork or the negative cable.
I would suggest you dont run the engine until you have installed the new battery - a voltage of over 13 volts with engine running will indicate all is ok.
 
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