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Electrical / Alternator question?

moresparks

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3 Apr 2007
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182
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Westwick - Essex
Hi hopefully someone can assist.
Is there any reason that the D+ of the alternator should be on the un-switched side of the House Battery Isolating switch?
I have a Volvo Penta engine with 2 batteries:
1/ Engine Start
2/ House Battery.
The Engine Start Battery is fed to the Alternator via a Battery Isolating switch in the normal way via a fuse, Starter Motor then B+ of the alternator.
The D+ is fed to the Instruments and a take off for other 12volt services. A feed is also to the house battery for charging. The Services is the other side of the switch i.e. switched, but I seem to have a permanent 12Volt feed from the house battery to the D+ of the alternator.
This causes a minor drain on the house battery, Apart from not being able to isolate the supply without disconnecting.
The switches are just the standard Battery Isolating Switches with the red key.
My only thought was that originally the boat had a very basic battery charger so this would not have charged the house battery on shore-power if the battery feed was on the other side of the switch. The charger has been replaced with a modern charger with separate outputs.
All other aspects are working just fine like normal charging when the engine is running.
Can anybody think of any other reasons as I am considering moving the supply to the switched side?
Thanks in anticipation.
 

Minchsailor

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N of Ardnamurchan, winter South of Oban
Seems odd. I have checked the wiring diagram for my engine (Betamarine 35, but they are all probably much the same) and the D+ connection is on the switched side of the battery.

Could it be something to do with voltage sensing - avoiding extra resistance/voltage drop.

Can't see mjuch harm in changing it.
 

VicS

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46,371
A diagram would help to understand your system.

You don't say how the output from the alternator is split to charge two batteries. ie diode splitter, VSR, or some other system.
Some VP engine alternators are fitted with a piggybacked diode splitter.

I am surprised that the instruments are fed from D+. Presumably you mean navigation instruments rather than engine instruments ( oil and temperature)

What engine is this .
 

moresparks

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3 Apr 2007
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182
Location
Westwick - Essex
I guess a picture would help – I will see what I can do.
The basic wiring has not been changed from the Volvo wiring diagram except that a second battery has been installed by the builders many years ago. There are no VSR’s just the normal Volvo Alternator.
Apologies, I meant navigation Instruments.
The engine is petrol A171C but the alternator is used on a number of Volvo Penta Diesel and Gasoline engines around the early 90’s.
The House battery is charging o/k when the engine is running and the feed to that battery appears to be from the D+.
 

pvb

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The D+ terminal is usually to provide field current, and is normally fed by the ignition switch, via a charge lamp. If it's connected permanently to the battery, there will be a constant discharge current through the field coil. You perhaps need to ask a marine electrician to check your wiring.
 

halcyon

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Volvo used to fit alternators with blocking diodes inside, so had a feed to each battery bank with a sense lead to service battery, may be what you have.

But all wire should go to switched side of battery isolator switch to stop drain when not in use and batteries off.

Brian
 

moresparks

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3 Apr 2007
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Location
Westwick - Essex
Many thanks for your responses – I must admit I was not entirely happy with the set-up, hence me asking the question. Much of the wiring disappears in to the bilges of the boat and impossible to get at or indeed trace, so there may be other problems lurking unforeseen.
I was thinking of adding another House Battery but needed to understand how this current system is set-up first.
 

VicS

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I guess a picture would help – I will see what I can do.
The basic wiring has not been changed from the Volvo wiring diagram except that a second battery has been installed by the builders many years ago. There are no VSR’s just the normal Volvo Alternator.
Apologies, I meant navigation Instruments.
The engine is petrol A171C but the alternator is used on a number of Volvo Penta Diesel and Gasoline engines around the early 90’s.
The House battery is charging o/k when the engine is running and the feed to that battery appears to be from the D+.
I take it you mean AQ171C

Wiring diagram in the manual does not show any connection to a D+ terminal but the parts diagram does show the diode splitter that can be fitted inside the alternator for charging a second battery.
My guess is that its additional output is labelled D,+ as appears to be the case, and which as Halcyon suggests should go to the switched side of the house battery isolator. Which is what you are proposing.

If there is a sensing connection it has yet to be identified, If there is it must be connected so that it always "sees" the alternator output, and not be connected to the opposite side of an isolator.

If you add a second house battery I would simply connect it in parallel with the existing one ( but see http://www.smartgauge.co.uk/batt_con.html for the best way of connecting multiple battery banks)
 
Last edited:

pvb

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Wiring diagram in the manual does not show any connection to a D+ terminal but the parts diagram does show the diode splitter that can be fitted inside the alternator for charging a second battery.
My guess is that its additional output is labelled D,+ as appears to be the case, and which as Halcyon suggests should go to the switched side of the house battery isolator. Which is what you are proposing.
For reasons which I've never understood, different alternator manufacturers use different designations for the connections. The D+ terminal may also be called 61, or IND, or L. So you may find that the engine's wiring diagram identifies the terminal using one of these alternative designations.

The diode splitter you referred to fitted on the back of the alternator, not internally, and just had 2 outputs marked +. I had one on my old boat, although it was remotely mounted (an option which VP offered).
 

VicS

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For reasons which I've never understood, different alternator manufacturers use different designations for the connections. The D+ terminal may also be called 61, or IND, or L. So you may find that the engine's wiring diagram identifies the terminal using one of these alternative designations.

The diode splitter you referred to fitted on the back of the alternator, not internally, and just had 2 outputs marked +. I had one on my old boat, although it was remotely mounted (an option which VP offered).
Yes that why I initially said piggy backed on to the alternator but the parts diagram seems to show something that fits inside the housing as Brian described it.

Terminal 61, IND, L or D+ is the connection for, usually, the ignition warning light although there is a resistor, rather than a warning light, on this engine to supply the initial excitation.

I not sure what would happen if that was connected directly to the house battery. It just should have a brown 1.6mm² (AWG 16) wire connected to it.
 

moresparks

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Westwick - Essex
O/k, now is starts getting strange and I feel more work needs to be done with the multi-meter to try and trace more wires. There is a brown wire about 1.6mm2 coming from the wiring loom but it’s been cut off, this is now too short to connect to the alternator. The wire that is connected to the D+ is 6.0mm2 and is also brown; this feeds to the un-switched side of the house battery isolating switch. From the switched side is a 6.0mm2 brown wire that feeds the main DC switch panel, which is what I would expect. There is also another wire 6.0 mm2 in red that looks like it should have gone to the alternator at some point but is also cut off. This looks like a parallel to another red wire connected to B+. It does look as though the 6.0mm2 brown wire is an original builders fit, comparing with the other wiring.
 

pvb

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Yes that why I initially said piggy backed on to the alternator but the parts diagram seems to show something that fits inside the housing as Brian described it.

Terminal 61, IND, L or D+ is the connection for, usually, the ignition warning light although there is a resistor, rather than a warning light, on this engine to supply the initial excitation.

I not sure what would happen if that was connected directly to the house battery. It just should have a brown 1.6mm² (AWG 16) wire connected to it.
Trust me, the add-on diode splitter is external - there isn't room inside an alternator!

If the D+ on the OP's alternator is wired permanently to the battery, it's incorrectly wired. He needs an electrician to sort it out properly.
 

halcyon

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Trust me, the add-on diode splitter is external - there isn't room inside an alternator!

If the D+ on the OP's alternator is wired permanently to the battery, it's incorrectly wired. He needs an electrician to sort it out properly.
The Volvo system had the diode splitter in the alternator back cover.

Brian
 

VicS

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Trust me, the add-on diode splitter is external - there isn't room inside an alternator!
That's what I thought too but I have learnt that Brian generally knows what he is talking about.

If the D+ on the OP's alternator is wired permanently to the battery, it's incorrectly wired. He needs an electrician to sort it out properly.

D+ can mean different things I think you will find.

If the OP's house battery is wired to the 61 ( warning light/ initial excitation terminal then it does need sorting out because it probably is not working properly and there will be a significant drain via the regulator if wired to the battery side of the isolator.

There seems to have been modifications made. Mods that at the moment I dont follow or understand.
 

pvb

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That's what I thought too but I have learnt that Brian generally knows what he is talking about.
Not in this case, the add-on diode splitter offered by Volvo Penta bolted on to the back of the alternator, not inside it.

D+ can mean different things I think you will find.

If the OP's house battery is wired to the 61 ( warning light/ initial excitation terminal then it does need sorting out because it probably is not working properly and there will be a significant drain via the regulator if wired to the battery side of the isolator.

There seems to have been modifications made. Mods that at the moment I dont follow or understand.
D+ is pretty specific, although as I've said it can be called different names by different makers. But you're right to repeat my advice that the wiring needs sorting out by someone who understands it.
 

moresparks

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3 Apr 2007
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Westwick - Essex
Hi Just an update.
Completely disconnecting the D+ wire and the alternator does not charge even when revved hard.
The alternator is a Prestolite 66021151MS and according to the circuit of this model then a D+ is required to “excite” the alternator. Normally this would be a 12v feed from the ignition switch with a warning lamp.
My guess is that the current D+ 12volt feed is from the house battery to supply the “excitation”. The thickness of the cable is probably to charge the house battery and was a factory install. The probable reason it was from the un-switched side was to prevent “user error” as if the battery switch was accidently not switched on, then neither of the batteries would be charged. Crude but effective.
Welcome to be corrected.
The alternator has been replaced in the past so just wondering if the current system of constantly feeding 12v to the D+ circuit is shortening its life?
I will have a think over the winter and maybe come up with a better solution like running a separate 12v cable from the ignition switch via a fuse and lamp. Then fit a Automatic Charge Relay to charge both batteries.
 

pvb

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My guess is that the current D+ 12volt feed is from the house battery to supply the “excitation”. The thickness of the cable is probably to charge the house battery and was a factory install. The probable reason it was from the un-switched side was to prevent “user error” as if the battery switch was accidently not switched on, then neither of the batteries would be charged. Crude but effective.
Welcome to be corrected.
My guess is it's been incorrectly wired. You have a permanent 24/7 current drain resulting from the incorrect wiring, which isn't something most owners would want.
 
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