24 volts from a 12 volt supply

[Mat-C]

Ok... let me preface this by saying that electrics is not my strong point, so please be patient with me if (when) I say something stupid...

I have a a pair of 12 volt batteries connected to supply my 12 volt house requirements.
I am looking at installing a thruster, but this requires 24 volts. I am rather loath to add a separate battery bank to supply it.
Is there a relatively idiot-proof way of achieveing this ??

[Bglad]

You need a series/parallel battery switch. Haven't installed one myself but they are used on engine starters so might work for a bow thruster.

[Willallison]

Mat, I've been looking into a similar installation myself. And whilst it is the obvious solution, much of the literature suggests that a series / parallel switch is a bit of a risky approach... if things go awry then they can have some pretty nasty consequences.
I'm still looking into what groupls like the ABYC recommend - perhaps someone else will know....
I did come across this... though I doubt it would pass muster with an ABYC committee
http://www.yandina.com/24VoltBattery.htm

[michael pierzga]

Go for a second battery bank. A Thruster draws huge amperage. If you are thrustering and picking up anchor with an electric windlass simultaneously, the load on your electric system is even greater. The primary method of failure for big electric motors and their relays is being starved for power. The primary cause of delicate electronic gear failure is voltage spikes caused by heavy loading of gear like thrusters.

The copper cables that you need to purchase to make long runs are large cross section, expensive and difficult to route correctly. Batteries are cheap.

Put a second battery bank close to the thruster then use a charging device to top it off. Its a better system an normally saves you money

[CDK]

Willallison provided a good, inexpensive solution.
You can use an auxiliary starter relay with the coil contacts wired parallel to the thruster relay. Then the 12 to 24 V switching is automatic.
The two halogen lamps I would mount in a perforated metal enclosure: they generate 100 watts when the thruster is operating and must be able to get rid of the heat.

[Bglad]

Instead of lights why not install switches in the parallel circuits too. Turn them off before you switch to 24 volt mode then back again when finished.

[CDK]

That is possible of course Bglad, but it involves two SPDT or one DPDT switch with 100+ Amps contacts, which are hard to find, bulky and expensive.
The headlights provide an excellent low cost solution. Because of their low resistance when cold the voltage drop during 12 V use will be minimal.

[Submarine Tom]

No question in my mind, independent batteries beside the thruster. Lowest: risk/hazard, cost, maintenance.

-Tom

[CDK]

I fully agree with your choice of location Tom, but the issue is how to charge them from a 12 V system. The OP uses the phrase "idiot-proof", so no manual switches.
A 12 to 24 V converter is no solution because it doesn't provide charging voltage.

[Submarine Tom]

Good point CDK, thanks.

How about a seperate, 24V charger next to the batteries...?

-Tom

[CDK]

Charging with shore power, sure....

To be honest I don't know if using shore power is customary in other parts of the world. I have the power grid just a few steps from my boat but hardly ever use it, except for electric tools and rare occasions when the solar panel didn't live up to its expectations in the winter.
But I am probably an exception.

[slow fred]

Minn Kota makes an onboard charger that charges each battery from the main engine battery. I have one and they work. Model MK-2-DC, price around $130.00, Bass Pro Shop.

[Boston]

that diagram was particularly helpful Mr Allison
thanks
B

[Mark Cat]

For engine starting, an old approach was to use a series-parallel solenoid.

There is no specific ABYC rule that prohibits its use to momentarily create 24V from two 12V. However, the application of this solenoid from ABYC clearly is for starting engines and not running loads, especially in relation to house and house emergency reserve.

I would install another alternator/regulator, batteries, overcurrent and controls to operate the new thruster.

Mark

[DaveJ]

Here is an idea, Change your alternator to 24V system, connect your two batteries in series with your 24v charging system.

You run all your engine systems across one battery and all the house stuff across the second battry.

And you can run your 24v thruster across the two batteries to get 24 v's.

Put safety measures in place to watch the engine battery so it does not get drain when using 24v system, but since the house system is only across the house battery the engine battery is isolated from house usage. You will need to isolate the 24v alt from the engine to ensure that 24v is not supply across the engine management systems.

Maybe two batteries in series don't charge that well, though it seems to work with normal NiCd batteries, they always seem to be in series.