Dual Batteries- How do people manage them?

[Getout]

Most offshore boats these days, have a couple of batteries linked by a battery isolator switch.
How do people manage them?
Run on "both" all the time?
Run half the day on #1 and the other half of the day on #2?
Save one for starting and use the other to run electronics?

I believe that you shouldn't change the switch setting when the motor is running. T/F?

My sounder switches off, due to voltage drop when starting on only one battery, so lately I have been leaving the battery switch on "both". Previously, I would start and run out to the fishing spot on one battery, then switch over to the second battery for the rest of the trip.

I'm sure that someone here knows how it should be done. I would appreciate some expert advice.

[Chimo]

HI GO

Firstly let me say that I am no expert on this but take advice when given and also act on it or whats the point in asking?

So given the above this is my system.

Two motors so two starting batteries; one for each motor. Cable connecting both batteries with an isolating switch. Left off unless and until one motor battery fails and then the switch is used to allow crook motor battery to be "supported", jumped. Once the motor is running disconnect motor batteries link and start the "good" side. I have had to do this only once while offshore and its quick and very handy!

The house battery (deep cycle) stays connected to all the house gear, sounders and GPSs and radios and stereo all the time.
House is charged automatically off the starboard motor with and Auto Battery Coupler (ABC) connecting and disconnecting the house from the motor battery automatically depending on the situation.
eg motor running voltage at 13.6 or so and the connection is made;
motor off, motor being started so voltage drops in motor battery so ABC disconnects house to avoid spikes etc impacting on GPS / sounder etc until motor running and voltage stabilizes.

The whole system was installed by the marine electrician / electrical engineer who designed and built the ABC and it seems to be idiot proof (which suits me) and does not need to be touched or adjusted by any crew who do not know what they are doing.

All I do is disconnect the two motor circuits when the boat is not in use by turning off the isolating switch for each motor battery and removing the plastic keys.

If your sounder switches off; the voltage must be very low and if it was my boat with your setup; I'd be turning the sounder off before starting the motor anyhow.

By the way this is what Lowrance told me do after I had a sounder / gps replaced by them on warranty after 2 yrs use when I noticed a few pixcels had "buggered off"

They gave me a new GPS / Sounder and said if I stuffed it again with spikes I was on my own which is when I did my research and found the Auto Battery Coupler and the guy to re wire the boat which fixed my problems well and truely.

Cheers
Chimo

[TimiBoy]

I have two, and I run them both for starting and running, but when stopping and running electronics, I switch to one. The motor will start easily on a single.

I ran the motor constantly Friday night with the radar running. It uses only a couple of litres an hour, and exhaust fumes are minimal (one occupant did get a little sick from the smell, he said. He's a sook!)

I look forward to seeing some expert advice here, too. I don't know whether I'm being paranoid by running like that.

Cheers,

Tim

[2manylures]

Just a thought for you blokes in sunny country. Have you thought of solar chargers that can be left on 24/7.

I was almost going to put one on my boat but my electrics don't warrant any auto charging system.

I did however spak to the appropriate engineer/technician at www.energymatters & for the small outlay if & when I upgrade my electronics/electrics etc i will seriously consider this inexpensive option.

Worth a thought & a ph call for more info.

[on-one]

I've got two house and two starting batteries linked by an isolator switch and also by a battery coupling device like the one chimo mentions. A solar panel feeds power into the house batteries, and the coupler allows the starting batteries to charge when the house batteries are full. Typically I start and run the boat on all batteries and then switch to house batteries at anchor. I'm no electrician so I've no idea if this is technically the best solution but it seems to work well

[mikeyh]

Chimo is on the money 100% with a well set up system. I never had the auto voltage sensing relays so all was manual......
For my single motor, twin battery set up, I used to rotate trickle charger between house and start batteries when not at sea. On a trip I would use start battery and run out to reef with it so I know it is 100%. Switch to house battery once at reef for sounder, fridge etc etc. If only a short trip boat would always start with house battery but you know that start battery is 100%. Bottom line if fridge, sounder stops not so tragic but very tragic if motor wont/cant start. If you are travelling a long way offshore and by yourself I would advise to replace batteries about every 2-3 years but dont do both at once...that way you can spread the pain and also minimise possibility of buying 2 batteries from the same (bad) batch. I always used a dedicated deep cycle battery for the house.......

in terms of moving the isolator switch when running............the only no no is turning the isolator to off when motor is running because that will fry your alternator ...switching between 1, 2 or 1&2 is no problem when underway.

cheers, Mike

[cormorant]

in terms of moving the isolator switch when running............the only no no is turning the isolator to off when motor is running because that will fry your alternator ...switching between 1, 2 or 1&2 is no problem when underway.

cheers, Mike[/quote]

Depends on type of switch and the way it changes fields

[Getout]

in terms of moving the isolator switch when running............the only no no is turning the isolator to off when motor is running because that will fry your alternator ...switching between 1, 2 or 1&2 is no problem when underway.

cheers, Mike

I think my isolator switch maintains circuit with one battery until the other is engaged so you might be right there.
Cheers
GO

[mikeyh]

Fair call Cormorant...I have only ever seen the type of switch where the field is always engaged...but you know what they say about assumptions..........

[peterbo3]

Pic shows Perko selector switch & BEP Voltage Sensing Relay. 1 is start motor, 2 is house. Selector switch stays on 1. When Batt 1 reaches 13.7V the VSR then puts power into Batt 2. This ensures that batteries are evenly charged at all times.

[cormorant]

Fair call Cormorant...I have only ever seen the type of switch where the field is always engaged...but you know what they say about assumptions..........

There is cheap and nasty out there as well and also some are built for specific purpose with generators on board. It is all about getting the right quality switch for the purpose.


Now to VSR

What happens if your start battery drops a cell and never reaches the VSR voltage. Your alternator beats it's brains out and the secons house battery never gets charged. Everything running off the house battery flattens it overnight and the next morning you are stranded with not a decent battery to start a motor with no pull cors. Just a thought as that is what 4wd guys have discivered with runig fridges overnight as an example.

Another stupid point is that many boat alternators / rectifiers don't put out exact voltages and some may not be able to charge batteries effectively if you don't choose the correct type. This may lead to the VSR never charging the second battery.

Independant dual circuit provided by a dual battery charge kit on the motor is a solution with low voltage alarms as it gives you total redundancy but you still have to check voltages to ensure batteries are accepting a charge and retaining it.

[Chimo]

Hi Cormorant

The point you raise about VSRs is I believe valid and that is why the setup on needs isolating switches to isolate the motor batteries when the boats not in use ( about $12 ea )plus the benefits from having an Auto Battery Coupler which connects and disconnects so as to maximize house battery charge while protecting the instruments being powered by the house battery during and immediately after the motor starting high risk period.

As per comments earlier in this thread, I suggest that the operation of the ABC is subtly different and more beneficial. ie Auto Battery Coupler (ABC) connecting and disconnecting the house from the motor battery automatically depending on the situation.
eg motor running voltage at 13.6 or so and the connection is made;
motor off, motor being started so voltage drops in motor battery so ABC disconnects house to avoid spikes etc impacting on GPS / sounder etc until motor running and voltage stabilizes.

The ABC also disconnects the house battery if the house battery is drained below a certain point too so there is power to start the motor.

The whole system was installed by the marine electrician / electrical engineer who designed and built the MarK 2 ABC ( the original one was built by Elis Rowe who has now retired) and it seems to be idiot proof (which suits me) and does not need to be touched or adjusted by any crew who do not know what they are doing.

If you or others you can shed light or show me where I have become confused please enlighten me for I still feel the VSR only goes part way to meeting our needs!

Cheers
Chimo

[Cheech]

I only use both at initial startup at the ramp. After that I switch to a battery 1. Depending on the trip length, I usually run battery 1 till I get out, and then switch to battery 2. Then stay on battery 2 for the rest of the trip. That way I always have a full battery 1 as backup. Then next trip if I remember, I will use battery 2 first, and switch to battery 1 for running around.

People talk about house batteries and operational batteries, but I like to consider both to be operational batteries that I just take turns in using.

I use to just leave it on both, but one time on my old boat I had a dud battery that did actually suck out all the power and kill the other battery. Not much fun trying to bull start the old 100hp merc I had. But we actually did do it. Never want to try again though.

Cheech

[Outsider1]

I do exactly the same as Cheech, have for years and it seems to work for me.

Cheers

Dave

[peterbo3]

As well as sensing an upper limit of 13.7V, the VSR has a lower limit. Once a battery drops below 12.8V, the VSR isolates it. This prevents a bad battery taking all the motor output.
The charge level of the house battery is displayed on the sounder so this can be monitored.
No system is perfect but the VSR seems to work for me. After I installed it I kept a close watch on charging rates via a multimeter.