Boat battery switch indicator

[macduff]

I have a switch on my boat which has four positions: Off, 1, Both, 2. 1 refers to battery bank 1, 2 refers to battery bank 2. The batteries are charged via the engine alternator. The centre of the switch main cable goes to the starter and all the other circuits, i.e. either bank 1 or bank 2 can be used to start the engine and power the circuits. Another main cable goes to the earth of the engine block. 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. My usual mode of practice is to use bank 1 for starting the engine, then turn off the engine and start sailing, then switch (going through Both) to Bank 2. Bank 1 is a starting type battery (thin plates). Bank 2 is a deep cycle battery (thick plates). My problem is that sometimes I forget to switch to Bank 2 !! This can run down Bank 1, which I need to preserve for just starting. I wondered if a circuit could be designed that would light a warning light all the time I was using Bank 1 ? I could install this warning light in the cockpit.

 

[BrownOut]

I'm a sailor too, so I'm going to give your question some thought

 

[BrownOut]

Ok, here is one solution. Get another battery, call it battery 3. It can be just a low-capacity one. Connect the positive terminal of battery 3 to the positive terminal of battery 1, but don't connect the negative terminal. Instead, connect an indicator light to the center main connection of your switch, and return the indicator light current to battery 3. Then, the indicator light should glow only when you're on battery1 ( or the "both") position.

The problem is that battery 3 will eventually run down. So, you might want to get ( or build) an isolated DC-DC convertor to put in place of battery3. If you do this, you can even power the convertor from battery 2.

Make any sense?

PS you can test this scheme while your at the dock, using a portable battery charger in place of battery3/DC-DC convertor.

 

[Quantised]

If you have a battery combiner then what is the point of the off,1,2,both switch. The batteries get charged by the combiner and so you could just wire the start bats to the engine and the #2 set to the house. In the odd occasion you need to combine them set the switch to both otherwise leave it off. It is a common way to do it and it will never fail you. I can draw you a diagram if you need.
By the way - what is the switch make and model as some have a secondary circuit switch for the field of the alternator which you could use? How big are the bats and the Alternator?

Quantised

 

[tinkerunique]

Another solution - like my pickup... Install a "battery isolator". Bat #1 is for most things / fuse panel /factory installed - Bat #2 is for accessories / install separate fuses. #2 is used for camper lights,winch, etc. and can be used to jump start others - or yourself when the lights are left on. Simple / not expensive / effective !! A meter can be wired in to show the % of charge in each battery.

 

[macduff]

Ok, here is one solution. Get another battery, call it battery 3. QUOTE]


OK. Thanks. I'll try that out next week. Sorry for the delay in responding. Went to visit the grandchild !

Cheers

 

[macduff]

Hello Brownout

I tried your possible solution just before I went on a 5 day cruise last week. Unfortunately, it didn't work. Here are the specifics:

1) When the -ve side of the indicator light was attached to any earth, it shone brightly.

2) When the -ve side of the indicator light was attached to Battery 2's +ve, it shone moderately

3) When it was connected to the middle connection of the battery switch, it came on dimly when the switch was at OFF.

I thought it might help if I listed what was connected to the various connectors. A circuit diagram is too difficult !

Here goes:

Battery 1 +ve:
To Linc battery monitor
To Windlass +ve switch
To Terminal 1 of the Battery Switch

Battery 1 -ve goes to a common Earth

Battery 2 +ve
Two connectors to the LInc battery monitor
To Terminal 2 of the Battery Switch
Shorepower charger
Inverter 800 Watt
Various house fused items: bilge pump, macerator, water guage, holding tank guage

Battery 2 -ve goes to a common Earth

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

I hope the above list can help you in coming to another possible solution !

Thanks very much. You are the only one interested in looking at the intersting problem !

Macduff

 

[RODALCO]

Somehow you need to sense the current in one of the leads from battery-1 and activate an alarm light with it.

I take it that when you start the engine of bat-1 and forget to change it over the auxillaries on the boat slowly discharge bat-1.

In ammeters often the voltage drop across the negative lead gets sensed and put into an opamp to drive a display of some sort.

During starting there may be 0.5 volts across the negative terminal and the massa point on the engine. With smaller loads it may be millivolts.

A circuit which senses between say 20 mV and 0.5 volts needs to be designed and trialled to make it work.

does that make sense ?

 

[tytower]

Look at low voltage cutouts for battery 1 . Oatley has one with an 80 amp latching relay which turns off at a set voltage . No power will soon remind you. An alarm from there will fixx this

https://www.oatleyelectronics.com/

 

[BrownOut]

I don't think you connected the light as I suggested. I think it will work if connected as specified.

 

[kchriste]

BrownOut, draw it out and you'll see why it doesn't work.

Another solution would be install a magnet on the switch handle and a reed switch on the body to sense the position of the switch. Quantised's solution is the way I would do it. Keep the battery isolator and wire the engine to bat1 and aux circuits to bat 2. Install a switch to parallel the two banks if needed.

 

[tytower]

BrownOut, draw it out and you'll see why it doesn't work.

I would have thought it would work OK as long as the negative terminal of battery 3 is not connected to any other earth. I suppose I will draw it and see. I am not sure about the connections on the battery switch . Does anybody know?

 

[BrownOut]

Thanks KChriste. There was an error in my scheme. The problem was that the circuit for battery3 was complete when battery 2 was being used, through battery 1. The problem is easily solved by adding a power diode to battery 1 ( see attachment ) The diode prevents current from battery 3 from flowing through battery1 when battery 2 is being used. The simulation verifies the operation.

Since battery1 is being used to start the engine, D1 has to handle the starting current, probably 100 - 200 Amps. Does anyone have a part number for D1 that will work? If not, I'll research it tomorrow.

In the attachment, battery1 is switched in for 2 seconds. Then battery2 is switched in for 2 seconds. Current through the lamp, represented in the drawing by R2, only flows during the time that battery1 is switched in.

V1, V2, and V3 represent battery1, battery2, battery3 respectively. V4 and V5 are not to be used in the final circuit, and exist for simulation purposes only.

 

[BrownOut]

It looks like the price for these diodes will be prohibitively high. I'll try to think of something to replace D1 with, if you still want to try this.

 

[BrownOut]

Ok, here is another idea. Current from battery1 turns on q1 and q2 via R3 and R4. The values of these resistors depend on how much current is being drawn. Q2 turns on the lamp, represented by R2. The starting current cannot be drawn through R3 and D1, thus the connection for the starter must be made at the junction of the switch and R3.

 

[Quantised]

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.

So a transistor across the + terminal of bat 1 and bat 2 can used to turn on an alarm when the volts drop below .6 volts. It is cheap to make and requires no other changes in the wiring of the boat. Maybe BrownOut can recomend a suitable transistor?

Quantised

 

[tytower]

It looks like the price for these diodes will be prohibitively high. I'll try to think of something to replace D1 with, if you still want to try this.

Depends on the size of the boat motor but if under 100HP then starter current is probably under 100Amps . Stripping an old alternator will yield 6 such diodes that if placed in parallel will take it for little cost. Use a second alternator and do a 12 Diode lump if need be.

 

[macduff]

Thanks for all the postings. A couple of comments. First, it's consdered desirable in the sailing world to be able to use either battery to start the engine. Normally, one battery is designated as the starting battery, and is a thin plate type, as used in cars and trucks. The other battery is a deep cycle battery, used to power lights and instruments when the engine is off and you are sailing. However, just in case the starting battery doesn't work, it's desirable to be able to use the house battery to start the engine. I know from experience this IS useful ! Secondly, the cables running from the batteries to the earth (the engine casing), the starter, and the alternator, are about as thick as a man's finger. Moving them from their current connections would be very awkward. Thirdly, insurance firms insist that you have a battery switch. A sailing boat in water and using electricity is considered a dangerous thing ! (If you have ever seen a boat on fire, as I have, due to electrical fault, you'd probably agree !). Unfortunately, this morning, I don't have time to look closely at Brownout's latest solution, except to remark that the current draw for the starting battery must be quite high. I'm starting a 25HP diesel motor, and the recommended battery size is at least 600MCA. The highest battery draw from the house battery is probably 12amps at 12 volts, when a couple of lights are on and the frig compressor starts up. I'll be back later tonight, when I'll carefully review Brownout's latest solution. Thanks very much for the postings !

 

[macduff]

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 -
Quantised

The return from the alternator goes to the common connector on the battery switch. There is a two minute delay from the alternator due to the smart charger.

But this solution seems OK ? Why is there a higher voltage on 1 ? Due to going through the combiner first ? There is a further delay of two minutes from the combiner before the current gets to B2 !

 

[BrownOut]

I'll be back later tonight, when I'll carefully review Brownout's latest solution.

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.