series/parallel switch

[Guest]

I am fitting out a steel cruiser in which I have installed a bowthruster. I am using the usual 12v Engine and domestic battery system but the bowthruster motor is 24v.As part of the deal I have been supplied with a series /parallel switch. I have also obtained three (slightly differing) wiring diagrams for this system (from the switch maker , the bowthruster maker and the supplying boatyard) which appear to indicate that the positive and negative inputs to the switch should be seperate. My problems are that the positive and negative from the batteries should be common for battery charging purposes and that the wiring diagrams are from foreign speaking sources. I would be grateful for any help or suggestios as to whom I can turn to for assistance. Many thanks

 

[Guest]

I tried to solve your problem some years ago in an industrial application, I could not make it work effectively because the charging system has to be totally isolated due to at least one of the batteries being connected in series. I would seriously consider fitting a 12 volt motor. Regards LW

 

[Guest]

Andrew

Series / parallel switching can be done but I don't think it is a particularly good idea.

The switch would have to be capable of taking the maximum charge/discharge rate of the battery, which for engine starting is considerable, 100A +.

I think a better idea would be a third battery in series with the engine starting battery which would give 24V earth to line voltage.

This would power the bowthruster only.

The arrangement is easier to draw than describe, if you want I could E-Mail you with a picture.

The third battery could be switched to parallel the other battery for charging with a switch that can take the charging rate of the battery or load current of the bowthruster, whichever is greatest. It needn't be a particularly big battery either.

 

[Guest]

Very Messy! Change to a 12v motor. Otherwise use a battery in parallel with the starter battery. Switching those level of currents would normally be done by relays rather than switches. The two start batteries would be in parallel for starting and charging. When you operated the thruster, they would be isolated from charging and connected in series to make up the 24v. (charging would continue on the service battery) The circuit would need close scrutiny to ensure break-before-make contacts to prevent momentary shorting etc. Also never a good Idea to mix batteries of different capacities and ages. Personally I wouldn't even think of doing it, Back to first sentance. Dick James

 

[Guest]

Andrew,

I must agree with everyone that series/parallel switching can be done, but I also don't think that it is a good idea. Having examined the problem recently of running both 12v and 24v from one bank of batteries I came to realize that any system for doing this is fraught with difficulties (and potential dangers), to say nothing of inconvenience in use.

Optimum answer (personal view) for an electric drive is to swap the 24v motor for a 12v one, despite any power loss.

If that's not possible, another idea is to forget the dodgy switch and install a dedicated 24v circuit. Add an old 24v alternator to the engine and run this to two extra batteries to power the system. Further details if required.

Good luck,

Mike

 

[Guest]

Andrew if you wish to use the 24volt motor you are best using an additional 12volt auxillary battery. This should preferably be the same as your existing battery otherwise you could have battery life problems.The switch you require is a two pole break before make change over switch rated at the current of the 24volt motor. The arm of one pole (A) is connected to the negative side of the new battery, output 1 (A) connects to the negative side of the existing domestic battery, output 2 (A) connects to the positive side of the existing domestic battery.The arm of the other pole (B) connects to the positive side of the new battery, output 1 (B) connects to the positive side of the existing domestic battery, output 2 (B) connects through a suitable fuse/circuit breaker to your 24 volt bow thruster. Normally you would leave the switch set to position 1 and this would have the effect of doubling your domestic battery capacity. To use the bow thruster set the switch to position 2. A relay of suitable ratings could be used instead of the switch.

 

[Guest]

Bergman Thank you for your suggestion that a third battery is added. I would be very interested in your picture if you could E mail me on wellsent@compuserve.com. The switch that I have is already is heavy duty Thanks again.andrew

 

[Guest]

WAIT there is a much easier way.

As the other contributors have said, series/parallel switching of batteries is VERY dangerous. You have heavy conductors and a heavy duty switch. You have two poles to switch. If everything doesn't work just right in the timing, you seriously short out one or both batteries and cause an explosion.

Check out the technique in the link below. It only requires a single pole single throw switch, and is inherently safe. Using this technique, you can have batteries of different age, different size, different style however you should not mix wet cell batteries with AGM or GEL cell types.

http://www.yandina.com/24VoltBattery.htm

 

[Guest]

You\'re right - that\'s much easier. And quite elegant! (nm)

 

[Guest]

Re: WAIT there is a much easier way.

Thats really clever

If you mount the headlights one either bow you will not only be able to go sideways but see where you are going as well.

Forget switching - go for this.

 

[Guest]

Re: WAIT there is a much easier way.

.

 

[Guest]

Excellent piece of lateral thinking - nm

.