Boat battery switch indicator

Quantised said:

There may be a simpler way.

When then engine is charging bat 1 it will have a higher voltage than bat 2 and will be at least 0.6 volts higher as you have a charge splitter - now when you stop the engine the voltage of bat 1 will fall below this 0.6 threshold and may even fall below the voltage of bat 2 after a while as the power is used from bat 1.



Quantised

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On second thoughts, I don't think that bat 1 will have a higher voltage as the return from the alternator is to batt 2 (see my listing above). Agreed ? I'll have to check this on next visit to boat.

My purpose for the indicator light is to notify me when the switch is at teminal 1. My usual mode of operation is to turn the switch to batt 1. Leave it there until I have cleared the harbour. Then when I have the sails up and the engine OFF, turn the switch to bat 2. But sometimes I forget to do the laast switch. This means the frig, lights, instruments, etg are now running on bat 1 - which can be a problem if i go to start the engine some hours later.

BrownOut said:

Don't spend too much time looking at it. I realized there are big problems with it, given your current configuration. I was up way too late working on it, and I neglected some important details. This is turning out to be harder than I first thought it would be. I'm still working on it.

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OK. Thanks very much. Yes, it does appear to be hard. I tried a couple of years ago to get a solution, but people gave up on it !

macduff said:

Battery Switch

Terminal 1:
To Battery 1
To battery combiner
To voltmeter guage

Terminal 2:
To Battery 2
To battery combiner
To voltmeter guage

Middle Terminal:
Starter and house lights, instruments
Return from alternator
Macduff

Click to expand...

Looking at your connections the alternator is fed direct to the middle terminal and when bat 1 is connected to middle terminal it will see the full output volts of the alternator. The bat 2 is now charged by the splitter (or combiner) and depending on the model and make it will usually have a 0.6 volt drop across it.

If it were, say, a Guest variety it would be a simple power diode that stops the charge from leaking backward. If it were some other make it could be a power transistor with some control but this would also most likely have a 0.6v drop across it.

So if the 'detector' were wired from the middle terminal to the #2 terminal it will show a 0.6 volt differance when bat 1 is switched and 0.0v when bat 2 is switched.

Now if the combiner is a relay? may not work but all the ones I have seen have a voltage drop. It is also important to find out what other wires are on the combiner circuit, even a model number might help with a search on www

Otherwise you may have to go to the yacht and measure the voltage to see what it really is.

I fully understand all your points about moving cables, insurance, isolation switches etc. One of the reasons I stopped using splitters and combiners was the heat they generate and risk of fire! (oh and the voltage droop)

Quantised

macduff said:

OK. Thanks very much. Yes, it does appear to be hard. I tried a couple of years ago to get a solution, but people gave up on it !

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If you got desperate, you could go back to the circuit with 3 batteries and the diode. Then you could use a standard Ford type soliniod to bypass the diode during engnie startup. Connect the soliniod coil to the "Accessory" output of your ignition switch, if you have one. That way, the diode would be bypassed before the starting current started flowing. Fuse the doide, and have extra fuses available.

The solution should work, but it's non-elegant. Before you implement such a hack, let us think about this a little more.

macduff said:

Another main cable is attached to the alternator and to bank 1. There is a battery combiner between bank 1 and bank 2, i.e. amps coming from the alternator will go to both batteries or which ever battery needs charging. .

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In your first post you show the alternator going to battery bank 1.

macduff said:

Middle Terminal:
Starter and house lights, instruments
Return from alternator

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In a later post it shows the alternator connected to the middle terminal of the switch.

macduff said:

On second thoughts, I don't think that bat 1 will have a higher voltage as the return from the alternator is to batt 2 (see my listing above). Agreed ? I'll have to check this on next visit to boat.
.

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And lately you think it may be connected to battery bank 2?

It would be a great help if when you are at the yacht you can get a good layout plan for these wires as it is going to key to solving the problem without major rewiring changes especially where the alternator wiring goes and how it interfaces with the combiner.

But if there is some wind go sailing and do it later.

Quantised
Broad Reach Club

Look for somewhere you can drill right through the switch while it is on battery 1 without doing any harm . Its only plastic after all . Poke a small magnet down the hole with a little epoxy so it sits in the fixed part. Then when set poke a reed switch down next to the magnet epoxied in the moving part of the battery switch. Wire up th leads to a lamp & power up . Easy ! I'm assuming your switch is a circular type that are in abundance . Do it from the back for neatness if you are able

The more I think about the soleniod idea, the less I think of it as a hack, and more I think it's a viable solution. Using this, you create two circtuits for battery1, one high current circtuit for starting the engine, and a second low current one for running the boat's systems temporarily till you switch over. Using the second, low current circuit opens up a myrid of possibilities for isolating this circuit for indicators. You would want to use a "continuous" type soliniod, like this one: **broken link removed** At over 40 bucks, this won't be the cheapest solution, but it works, will be reliable and uses available parts. This soleniod offers high starting current, and more than sufficient running current. It would most likely be very reliable, and should it ever fail, you can just bypass it to get back to shore.

Quantised said:

And lately you think it may be connected to battery bank 2

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My apologies - the alternator return IS connected to the common terminal of the switch. It is NOT connected to bank 2 ! An error caused by trying to quickly reply when the wind was blowing !

But will your solution work in the following sceanarios:

1) I've started using b1, but forget to switch to b2 when I switch the engine off (the case I am most concerned about).

2) I've had to start using b2, because b1 is flat. In this case the switch will be at b2, so no light should appear. The circuit wouldn't be blown due to the high current drawn from b2 ?

3) I think we need to differentiate between when the engine is running (i.e. alternator procuding current), when it isn't, and when I'm using the shore power charger. I never use the alternator and shore power together.
3.1) When I'm using the alternator, the switch could be on b1 or b2 or BOTH (the latter I hardly ever use). I guess it would complicate matters tremendously if I wanted the indicator to come on for when the switch is at 1 or BOTH ? When using the alternator, yes, the amps will flow to b1 first and then through to b2 via the combiner, so there could be a voltage drop. When I switch to b2, with the engine running, i.e. the alternator working, the light will go off ? What happens if the switch is at BOTH ?
3.2) The light will come on when I switch back from b2 to b1 to start the engine so as to enter harbour ?
3.3)But when on shore power, when I really don't care at what terminal the switch is pointing, (as long as it is NOT OFF - see below) it could be that the switch is pointing at b1 (having just come back into harbour from sailing)However, the shore power is directly attached to b2 (since that is the battery that is being used at the dock). Will the indicator light come on then ? I don't think so, because now we have the reverse of the alternator case ??

At any rate, thanks for all the postings, because I have realized something as follows !! My shorepower charger is a TRUECHARGE 20, a smart charger. It has two outputs for connecting to two banks of batteries. Up to a week ago, I was using both outputs, one to b1, the other to b2. But I have just replaced one of the batteries, and from what I read, it appeared, that because I was using a combiner, it was better for the charger to only use ONE output. So I removed the connection to b1. Previously, it didn't matter if the switch was pointing at OFF, 1, 2, or BOTH. NOW I realize that it must be pointing at 1, 2, or BOTH for b1 to receive any needed charge !! Enough for now.

BrownOut said:

Connect the soliniod coil to the "Accessory" output of your ignition switch, .

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No sorry, NO Accessory switch !!

Basic key turn on, which provides power to glowplug solenoid push button switch, fuel pump, and push button start switch. (Once upon a time, I had to keep the glowplug button pushed in while I was pushing the start button. I changed that so the start push button had power directly ! i.e. I could release the glowplug button when I pushed the start button). Electrics on a boat are somewhat strange !

macduff said:

No sorry, NO Accessory switch !!

Basic key turn on, which provides power to glowplug solenoid push button switch, fuel pump, and push button start switch. (Once upon a time, I had to keep the glowplug button pushed in while I was pushing the start button. I changed that so the start push button had power directly ! i.e. I could release the glowplug button when I pushed the start button). Electrics on a boat are somewhat strange !

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That's perfectly fine. The idea is that accessories ( glow plug, etc. ) are powered on before energizing the starter motor. If you decide to split the power from battery1, this ignition switch scheme will work just fine.

macduff said:

2) I've had to start using b2, because b1 is flat. In this case the switch will be at b2, so no light should appear. The circuit wouldn't be blown due to the high current drawn from b2 ?

Click to expand...

The way I see this working is that there will be a 0.6v drop across whichever battery is not connected to the middle terminal. In that case you may have a green light that shows bat 1 is connected and a red light that shows bat 2 is connected.

If you switch to ALL then there will be no 0.6v drop to either bat 1 or bat 2 from the centre terminal because they are hard wired by the switch together.

This system is a detector system and has no power flowing through it so starting engines or drawing power will not blow anything, think of a voltmeter across the middle and bat 2 - you will see 0.6v but the meter wont blow up if you start and engine - so a simple voltage comparison circuit can turn on or off lights as you choose with simple logic. That part comes later after you have actually measured the voltage drop.

Once you confirm the voltage drops I can draw you a diagram but not today as we are hauling, pressure washing and blocking, a very stressful day for all.

Quantised

Going to boat tomorrow. Will measure voltages across whatevers ! Lookout for numbers late on Thursday morning !

Macbeth

Lucky you! I hope to get to my boat this weekend.

Quantised said:

The way I see this working is that there will be a 0.6v drop across whichever battery is not connected to the middle terminal. Quantised

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Measured this afternoon with battery switch set at 2. No discernable difference between voltage of B1 and B2 !! Combiner working. Charger was delivering 13.5 volts to each. 11 amps to B2 (house), 4 amps to B1 (starting).

Now what ?

Both tytower and I suggested the same simple solution using a magnet and reed switch:

tytowers (post #26):
https://www.electro-tech-online.com/threads/boat-battery-switch-indicator.95187/#post779140

Mine (post #11):
https://www.electro-tech-online.com/threads/boat-battery-switch-indicator.95187/#post778792

So it appears you have a relay type combiner, shame as this will not produce any discernable drop that you can reliably detect.

I am with tytowers and kchriste in a modification to your switch, either a magnet and reed relay or an opto-electric detector is going to be the way to go. You may have to drill out the rivets to open the switch if its a Perko and replace them with suitable bolts but if its a Guest or a Blue Sea Systems they can both be unscrewed to get to the inside. It would be really easy to glue on the magnet or stick a piece of reflective tape onto the rotor face.

IF you have a switch with an auxilliary field switch that is not used you could open up the switch, change the lands inside so it is only making contact when in bat 1 position and then use this to drive your alarm.

Let us know which way you go.

Quantised

Yes, I agree, the magnet solution seems to be the way to go. Got to put this on a back burner for a couple of days. I have REAL problems with refrigeration system and steering !!

Thanks for all the postings everyone. I'll be back in a couple of days.