My circuit diagram doesn't look right, help please?

[Quidi Vidi]

Hi
I am in the process of rewiring "Quidi Vidi" but i don't understand how it has been wired. I want to seperate the batteries and do away with the 1 2 off both switch, install a VSR and seperate battery isolator switches, emergency paralleling will be by a jump lead. I have removed the alternator and was surprised to find there are no cables going from it to the battery or starter. Everything is connected by 1.5mm sq cables except the battery to starter which is 50mm sq. I have found a wiring diagram in the manual which i have attached but it doesn't make sense to me. I would expect the alternator to be connected to the battery by a big cable and the ignition light to be connected to the aux on the alternator. Should i stick with the circuit diagram and use heavier cables or could anyone suggest a simpler layout that i could use?

 

[Bru]

Don't understand that circuit diagram

The battery positive appears to be connected to the ammeter negative

The oil pressure switch appears to short out the alternator

Something not right somewhere

Need to scratch my head and work out WTF is going on but a bit short of time right now, will try and have a proper look tomorrow

 

[prv]

Don't understand that circuit diagram

I don't fully understand it either, but I have a couple of thoughts:

The battery positive appears to be connected to the ammeter negative

So what? The ammeter shows how much current is passing through it. Doesn't really matter which way, especially since the picture of the panel shows a centre-zero meter. Just depends whether you want to see charging as positive or consumption as positive.

The oil pressure switch appears to short out the alternator

I think it's meant to be connected to the field coils, so that when the engine is stopped (no oil pressure) there's no field and hence less (mechanical) resistance from the alternator. The idea is to make it easier to start, then as the oil pressure rises the field kicks in and the alternator starts charging. I agree that as drawn it doesn't quite seem to do that though.

Pete

 

[Quidi Vidi]

Don't understand that circuit diagram

The battery positive appears to be connected to the ammeter negative

The oil pressure switch appears to short out the alternator

Something not right somewhere

Need to scratch my head and work out WTF is going on but a bit short of time right now, will try and have a proper look tomorrow

Thanks, i thought it was just me being thick, I'm no expert but i do understand the basics. I want to scrap this layout and simplify things, for instance i cannot see the Ammeter working as there is no shunt so i'm happy to leave that out. I'm also happy to leave out the oil pressure switch although it was probably meant to stop the alternator kicking in until the engine was running to aid starting.
That leaves me with an alternator, starter, glow plug, ignition switch and light. There is no relay or timer on the glow plug. Any suggestions as to how to cable these together and cable sizes would be very much appreciated

 

[halcyon]

i cannot see the Ammeter working as there is no shunt so i'm happy to leave that out. I'm also happy to leave out the oil pressure switch although it was probably meant to stop the alternator kicking in until the engine was running to aid starting.

The shunt is in the ammeter, shows charge to the battery, in the plus, out the minus.

The oil pressure switch is isolating possibly a voltage sense lead, or field supply to the alternator when the engine is not running, if not you will have a drain on the battery.

By the time you have simplified it, it may well be more complicated than yoy have now.

Why use jump leads, if you are fitting a VSR ?

Brian

 

[VicS]

Likewise I'm not absolutely sure I follow it.

BUT

The ammeter probably either has an internal shunt or is a moving iron meter.

Its not at all uncommon to see systems without remote shunts ( None of the Volvo diagrams I have looked at for example have remote shunts)

(The reason for using remote shunts is to avoid long runs of cable to the instrument panel and back again carrying large currents. A sensitive meter movement is used and it is connected to the shunt with light wiring. Most of the current flows through the shunt and just a few mA through the meter)

Not clear from the diagram but i suspect the oil pressure switch is one that closes when the oil pressure rises. Until it closes there is no field current so the alternator does not generate. It avoids putting a big electrical load on the engine until is is up and running properly.
IIRC there is someting in TONY BROOKS' Electrical notes about the system.


Beaten by Brian!

 

[prv]

By the time you have simplified it, it may well be more complicated than yoy have now.

Quite possibly, but he will definitely understand it.

I didn't bother trying to figure out the existing corroded spaghetti on my boat, just ripped it all out wholesale and started from scratch with a sensible layout, diagrams, and a labelling machine.

Pete

 

[Quidi Vidi]

Why use jump leads, if you are fitting a VSR ?

Brian[/QUOTE]

The jump lead will be used in an emergency if i need to use the domestic battery to start the engine to keep costs down for now

 

[halcyon]

The jump lead will be used in an emergency if i need to use the domestic battery to start the engine to keep costs down for now

Depending on the VSR you pick, it may do the emergency linking for you, thus no jump leads.

Brian

 

[pvb]

The jump lead will be used in an emergency if i need to use the domestic battery to start the engine to keep costs down for now

I think Halcyon was referring to the fact that some VSRs (including the ones he sells) have the ability to parallel the battery banks for emergency starting.

 

[Quidi Vidi]

I understand the principle of the oil pressure switch switching the field on once the engine has started but it seems to be wired in series with the ammeter which is wired in series to the ignition light and then to the ignition switch. As i understand it the ignition light is normally wired to the field to energise the field and then goes out once the alternator is providing a charge, i cant see how the pressure switch can work in series with this. Also all the cables are 1.5mm sq, surely they cant handle the charge through all these bits and then charge the battery. Should i upgrade the cables and if so what size? or should i add a heavier cable straight from the alternator to the solonoid/starter? The alternator is a Lucas/Marelli 45 amp (12745) it has 2 large male spades (connected together) and a smaller one in a recess. I believe the larger ones provide the charge and the smaller one is the field/aux? There is also a B+ stud which is not used but also provides the charge if necessary and one marked W which i think is for a rev counter?

 

[Quidi Vidi]

Quite possibly, but he will definitely understand it.

I didn't bother trying to figure out the existing corroded spaghetti on my boat, just ripped it all out wholesale and started from scratch with a sensible layout, diagrams, and a labelling machine.

Pete

Exactly, there are wires everywhere, hanging out of chocolate blocks and some frayed and broken. I thought it would be a good idea to replace them but i really dont understand this system and i have never designed a new one (or replaced one for that matter so on a steep learning curve)

 

[VicS]

I understand the principle of the oil pressure switch switching the field on once the engine has started but it seems to be wired in series with the ammeter which is wired in series to the ignition light and then to the ignition switch. As i understand it the ignition light is normally wired to the field to energise the field and then goes out once the alternator is providing a charge, i cant see how the pressure switch can work in series with this.

The output from the alternator flows from terminal 4 to the + terminal of the ammeter, through the ammeter and then from the -ve terminal to the battery via the terminal on the solenoid.
The ammeter only shows the output of the alternator.

The other wire on the -ve terminal of the ammeter is the feed to the starter switch. ( in effect from the battery)

The other wire on the +ve terminal of the ammeter is the supply to the alternator field via an oil pressure sensing switch. The alternator is not excited until the oil pressure switch closes.
You do not appear to have a warning light.

The wiring carrying the alternator output (to and from the ammeter) ought to be heavier than 1.5mm² although even that run singly and with free ventillation could safely carry up to around 30amps continuously.

 

[Quidi Vidi]

The output from the alternator flows from terminal 4 to the + terminal of the ammeter, through the ammeter and then from the -ve terminal to the battery via the terminal on the solenoid.
The ammeter only shows the output of the alternator.

The other wire on the -ve terminal of the ammeter is the feed to the starter switch. ( in effect from the battery)

The other wire on the +ve terminal of the ammeter is the supply to the alternator field via an oil pressure sensing switch. The alternator is not excited until the oil pressure switch closes.
You do not appear to have a warning light.

The wiring carrying the alternator output (to and from the ammeter) ought to be heavier than 1.5mm² although even that run singly and with free ventillation could safely carry up to around 30amps continuously.

Thanks, that kind of makes sense to my limited knowledge, I'm not used to reading circuit diagrams but your explanation has helped it make a bit more sense.
There is a light on the boat between the Ammeter and the ignition switch although its not shown on the diagram, should i bypass this or do you think it would still act as a warning lamp if the alternator should stop working? I assume the Ammeter would serve the same purpose although it wouldn't be accurate and do i really need to know how many amps the alternator is chucking out? Should i bypass this instead or keep them both?
I think i will upgrade all the cables to 2.5mm sq, the switch and battery are only about 1.5m from the alternator/starter. Would you agree?
How much current does a glowplug draw, would 2.5mm sq be enough? I have some 6mm sq if needed

 

[pampas]

I assume this is a single cyliner engine? The oil pressure switch is as stated allow the engine start with no alternator excitation. that wire would be 1.5mm sq. and any warning light that you may want to fit shound be in that line also. if the engine IS a single cylinder. one glow plug will take about 5 amps that could be 1.5mmsq as well.

The alternator wiring needs to be larger up to the ammeter and then to the battery , so the original circuit is correct for cable size except for the alternator wiring. Hope that makes sence.

 

[VicS]

There is a light on the boat between the Ammeter and the ignition switch although its not shown on the diagram, should i bypass this or do you think it would still act as a warning lamp if the alternator should stop working

From where to where exactly? When does it come on? when does it go out?

Puzzled at the moment!.

How does the start switch operate.?

Cannot tell you what current the glowplug takes, no idea. I'd have to measure it or measure its resistance . The latter might not be easy to do accurately!
Several amps no doubt but 1.5mm² will be adequate I'd think

 

[Quidi Vidi]

Yes it is a single pot
The light comes on when it feels like it really although i haven't run the engine many times so i cant really give you much info on that. The switch key has 3 positions, off, on and then start which is sprung back, all clockwise. I have bought a 4 position switch to replace it which has the same positions but with an additional sprung back one anti clockwise for heat. The glow plug hasn't been working and neither has the charging circuit which is why i have decided to replace it all, the alternator has been checked and is working as it should

Hope this helps

 

[VicS]

If you call the switch positions 0,1 and 2 I'd think "0" is the normal running (or off) position, position "1" energises the glowplug position "2" cranks the engine possibly while keeping the glowplug energised.
One the engine fires let the the switch return to "1" and then return it to "0" after a very brief delay.
Maybe the glow plug is burnt out, perhaps as a result of not being switched off once the engine is running. Easy enough to check with a multimeter ... it should have a very low resistance..... or even with a bulb on a couple of leads.

The switch you have bought probably will not keep the glow plug energised while cranking. Almost certainly if you use the anticlockwise position for it. The sprung anticlockwise position is what you would use to operate a stop solenoid in the fuel system.

 

[Quidi Vidi]

VicS, thanks for the advice, i was wondering how the switch worked regards the glowplug. I have ordered a new glowplug and in the meantime i have managed to get the old one cleaned up and working off the boat so next time i get down the boat i will give it a try. I always thought (or read somewhere) that you shouldn't switch the ignition off when the engine is running so this probably confused me into operating the switch incorrectly. I will give the old switch another go once i have replaced all the wires and cables, refitted the alternator etc. etc.
Once again you guys have given me the confidence to have a go at something i didn't really know anything about, this has increased my pleasure of boat ownership no end, thanks everyone

Next project, the domestic electrics so watch this space!!!! (Or hide)

 

[Bru]

Looks like it's all been said already by the time I've woke up enough to switch some brain cells on

I would definitely beef up the cabling to/from the battery as suggested