Alternator connection

[Sarnia]

I have been considering changing my alternator to a higher output, have discussed this in a previous post, today, back on the boat, I took it off and it is higher than i thought, is 65 amp, not 35 as anticipated, a Lucas NAB305, been on the boat over 10 years now.

The question i have is that when running the engine at 1500, the engine gauge shows 30 to 40 amps, whilst mt BM1 battery indicator only shows 10 to start then drops to 6 or 7, the feed from the alternator diaspears in a loom somewhere, I sus[ect to my BATT1, BATT2, BOTH switch.
Checking my BMI instructions it says all feeds must go to the shunt, as my solar panels do, is this the reason i am not getting an accurate reading, or am I?

I could of course with some work trace the alternator feed, any help or advice welcome , thank you.

 

[VicS]

I have been considering changing my alternator to a higher output, have discussed this in a previous post, today, back on the boat, I took it off and it is higher than i thought, is 65 amp, not 35 as anticipated, a Lucas NAB305, been on the boat over 10 years now.

The question i have is that when running the engine at 1500, the engine gauge shows 30 to 40 amps, whilst mt BM1 battery indicator only shows 10 to start then drops to 6 or 7, the feed from the alternator diaspears in a loom somewhere, I sus[ect to my BATT1, BATT2, BOTH switch.
Checking my BMI instructions it says all feeds must go to the shunt, as my solar panels do, is this the reason i am not getting an accurate reading, or am I?

I could of course with some work trace the alternator feed, any help or advice welcome , thank you.

Your BM1 should only show the net drain or charging current of the house battery bank.
It is possible that the alternator is simultaneously charging all the banks and supplying current to other equipment. The engine ammeter is very likely to be showing the total output from the alternator.

Quite possibly nothing wrong, just showing different things.

 

[Billjratt]

The fact that you mention solar panels probably means the alternator will never have much work to do - certainly after 10 minutes or so.
So the 65amp job is more than adequate. Does the alternator charge all of the batteries, or do you have to manually choose (1-b-2-off sw)
If the existing system is working OK, don't fix it. However you could think about a splitter and re-think where the measurements are being taken.

 

[Sarnia]

The fact that you mention solar panels probably means the alternator will never have much work to do - certainly after 10 minutes or so.
So the 65amp job is more than adequate. Does the alternator charge all of the batteries, or do you have to manually choose (1-b-2-off sw)
If the existing system is working OK, don't fix it. However you could think about a splitter and re-think where the measurements are being taken.

I have a batt1 batt2 both, switch, i know i charge the domestic seperatly by selecting batt1, and the starter battery by selectinf batt2, they can botthe be swiched off.

 

[Jim@sea]

One of the mistakes I have made is changing from a Lucas Alternator set up to a modern High Output Alternator and it has cost me a fortune to sort out.
My boat had a 1984 Lucas Alternator connected to a Lucas Regulator and Lucas Relay. (And in 1984 at my garage I was always having problems with Lucas Regulators and the don't even make them now)
So I bought a new High Output Alternator with an internal Regulator and I could not work out how to wire it up.
So I asked a local Auto-Electrician who could not work out how to wire it up. (Cars have Positive & Negative) (Boats have Positive, Negative and Earth.)
So I ended up having to get a Boat Electrician from 30 miles away to wire it up (£180) This is the disadvantage of having a boat in a marina where there are no qualified mechanics etc

I suppose it should be better but if I could have found a New Lucas Regulator I would have bought a second Lucas Alternator as a spare and probably saved £200.

 

[nigelmercier]

The answer to almost all alternator problems: http://www.balmar.net/regulators.html

 

[Sarnia]

One of the mistakes I have made is changing from a Lucas Alternator set up to a modern High Output Alternator and it has cost me a fortune to sort out.
My boat had a 1984 Lucas Alternator connected to a Lucas Regulator and Lucas Relay. (And in 1984 at my garage I was always having problems with Lucas Regulators and the don't even make them now)
So I bought a new High Output Alternator with an internal Regulator and I could not work out how to wire it up.
So I asked a local Auto-Electrician who could not work out how to wire it up. (Cars have Positive & Negative) (Boats have Positive, Negative and Earth.)
So I ended up having to get a Boat Electrician from 30 miles away to wire it up (£180) This is the disadvantage of having a boat in a marina where there are no qualified mechanics etc

I suppose it should be better but if I could have found a New Lucas Regulator I would have bought a second Lucas Alternator as a spare and probably saved £200.

How to connect one is also a concern for me, and you have pre-empted the next question here, which is a fount of all things boaty.

I am not sure, not having traced the wiring back yet, whether i have any other Lucas component in the charging circuit, but anyway i would wish to start from scratch when rewiring, best to start a new thread I think to deal with that.

 

[RAI]

Your BM1 will only measure the current through its shunt, which is probably fitted to the domestic battery bank. Any other current, going for example to the starter battery or bypassed loads, will not be measured. The engine ammeter is lot likely to be very accurate and even the BM1 might need calibration. It's even possible that your engine ammeter is wired to bypass the BM1 shunt.

 

[Sarnia]

Your BM1 will only measure the current through its shunt, which is probably fitted to the domestic battery bank. Any other current, going for example to the starter battery or bypassed loads, will not be measured. The engine ammeter is lot likely to be very accurate and even the BM1 might need calibration. It's even possible that your engine ammeter is wired to bypass the BM1 shunt.

Exactly, whether it, the engine amp meter is not via the BM-1, i do not know but probably not as it was there long before the BM-1.
My query is how can i get the actual chatge shown on the BM-1.

 

[Sarnia]

The answer to almost all alternator problems: http://www.balmar.net/regulators.html

Thank you Nigel

 

[Birdseye]

I have been considering changing my alternator to a higher output, have discussed this in a previous post, today, back on the boat, I took it off and it is higher than i thought, is 65 amp, not 35 as anticipated, a Lucas NAB305, been on the boat over 10 years now.

The question i have is that when running the engine at 1500, the engine gauge shows 30 to 40 amps, whilst mt BM1 battery indicator only shows 10 to start then drops to 6 or 7, the feed from the alternator diaspears in a loom somewhere, I sus[ect to my BATT1, BATT2, BOTH switch.
Checking my BMI instructions it says all feeds must go to the shunt, as my solar panels do, is this the reason i am not getting an accurate reading, or am I?

I could of course with some work trace the alternator feed, any help or advice welcome , thank you.

Back to basics. Amps cant just disappear. If they were being "used" in your switch it would get as hot as hell. Indeed having a feel round can sometimes be a good way of detecting bad connections / high resistance circuits. Grope your wiring my man and see if anything anywhere is getting hot.

Assuming that both your meters are right ( and that is an assumption) and that they are both reading the full current flow ( ie one of them is not domestic battery only) then the difference between alternator output and the lower current merasurement has to be electricity used to run some onboard facility. Mind you it sound too much for that - even my SSB on transmit is only 12 amps and everything else is a lot less.

 

[Sarnia]

Back to basics. Amps cant just disappear. If they were being "used" in your switch it would get as hot as hell. Indeed having a feel round can sometimes be a good way of detecting bad connections / high resistance circuits. Grope your wiring my man and see if anything anywhere is getting hot.

Assuming that both your meters are right ( and that is an assumption) and that they are both reading the full current flow ( ie one of them is not domestic battery only) then the difference between alternator output and the lower current merasurement has to be electricity used to run some onboard facility. Mind you it sound too much for that - even my SSB on transmit is only 12 amps and everything else is a lot less.

My concern also, but the BM-1 only reads via the shunt, and the alternator does not seem to be connected to it as a faily recent addition, so presumably not connect.

 

[RAI]

Exactly, whether it, the engine amp meter is not via the BM-1, i do not know but probably not as it was there long before the BM-1.
My query is how can i get the actual chatge shown on the BM-1.

If the shunt is the only thing connected to the domestic bank, then it will see all the current to and from it. If any wires reach the battery directly, bypassing the shunt, the BM1 will not measure the current through them. Don't worry about the alternator, look what gets to the batteries.

 

[Sarnia]

If the shunt is the only thing connected to the domestic bank, then it will see all the current to and from it. If any wires reach the battery directly, bypassing the shunt, the BM1 will not measure the current through them. Don't worry about the alternator, look what gets to the batteries.

The shunt is the only thing connected to the domestic bank, for both load and solar panel input, but I think the alternator feeds the batteries (2 x 180amph) direct, the BM-1 shows charging when alternator running, despite, i am pretty sure, the alternator, when BATT1 selected, feeds directly to domestic bank, also when BOTH selected, and much less when BATT2 selected alone, which is the starter battery which is usually well charged.

 

[RAI]

The shunt is the only thing connected to the domestic bank, for both load and solar panel input, but I think the alternator feeds the batteries (2 x 180amph) direct, the BM-1 shows charging when alternator running, despite, i am pretty sure, the alternator, when BATT1 selected, feeds directly to domestic bank, also when BOTH selected, and much less when BATT2 selected alone, which is the starter battery which is usually well charged.

Puzzling. The alternator can only feed the 2 x 180 Ah batteries through a wire. If no wires bypass the shunt, the alternator must charge through the shunt, so it's current would be measured when BATT1 or BOTH are selected. It should show no current going into BATT1 (the domestic battery bank) when BATT2 (starter) is selected alone. Unless, some other source, like shore power or solar panel is bypassing the switch and feeding only BATT1.

 

[Sarnia]

Puzzling. The alternator can only feed the 2 x 180 Ah batteries through a wire. If no wires bypass the shunt, the alternator must charge through the shunt, so it's current would be measured when BATT1 or BOTH are selected. It should show no current going into BATT1 (the domestic battery bank) when BATT2 (starter) is selected alone. Unless, some other source, like shore power or solar panel is bypassing the switch and feeding only BATT1.

Yes your correct it is puzzling, having checked at the shunt, installed in the last 12 months when I added the second 180 to the domestic bank, I cannot find any feed from the alternator.
You are correct, there is no current shown when after starting the engine with BATT2, the starter motor battery, until I switch BATT1 on and switch off BATT2.
The BM-1 reads the charge from the alternator then, despite, and I will re-check again, it not being via the shunt, unless it is somehow, but it shows the charge exactly the same as pre-installation of the BM-1. The solar panels are connected via the shunt ok.
I am awaiting the delivery of a new alternator, a Prestolite 14.4v 90 amp. should I ignore and or isolate the existing wiring from the existing alternator, and start from scratch and connect the new one to the shunt, is there any reason why not?

 

[LadyInBed]

You need to draw a circuit diagram to understand what is connected via what to what, which means tracing each wire from end to end.
PS
I assume that you have checked that the replacement alternator has the same dimensions as the old one regarding mechanical fit and alignment.

 

[Sarnia]

You need to draw a circuit diagram to understand what is connected via what to what, which means tracing each wire from end to end.
PS
I assume that you have checked that the replacement alternator has the same dimensions as the old one regarding mechanical fit and alignment.

Thank you, yes i have after some searching found a replacement with dimensions that will fit my set up, I made a scale drawing to compare with spec sheets of various Pretolite models.

 

[Sarnia]

You need to draw a circuit diagram to understand what is connected via what to what, which means tracing each wire from end to end.
PS
I assume that you have checked that the replacement alternator has the same dimensions as the old one regarding mechanical fit and alignment.

I think I will need to trace each wire to establish where from and to, they disappear into looms but it can of course be done, have resisted it so far but now I think I should be attemted.

 

[Sarnia]

You need to draw a circuit diagram to understand what is connected via what to what, which means tracing each wire from end to end.
PS
I assume that you have checked that the replacement alternator has the same dimensions as the old one regarding mechanical fit and alignment.

I have now traced the circuit to know what connects to what.
The alternator charging voltage/current is directly connected to a small but thick busbar to which my two battery switches are fed, and who in turn then are connected to the batteries. The switches are old style ones, very strong, one is for alternator feed to the domestic bank, the other is to the starter battery, they can be on independently or both together. The alternator is negatively grounded. So the alternator output does not go to the shunt as I suspected, but the BM-1 does read charging amperage when engine running.
There is a smaller cable also connected to the busbar, which I suspect may go to a 'percentage of charge' meter, made by Neco marine, in the control panel with the c/bs.
My question now is, do I connect the output of the new alternator in the same way, or should it be wired to the shunt, and if so how should I feed the Batt1, Batt2 busbar so I select as required.