Charging a 24v bank from 12v alternators

[stefan_r]

I have plans to install a 24v bow thruster with dedicated batteries but the rest of the boat is 12v.

I have been told charging is do-able but needs a box of tricks to make the magic happen.

Thoughts / ideas / guidance?

Cheers


PS - yes, deliberate choice to overcomplicate matters with a 24v thruster...some history there.

 

[nimbusgb]

This looks like just the ticket!

12v in 24v out charger

 

[Norman_E]

Charging at 4 or 5 amps with a 12 to 24 volt step up charger is going to be pretty hopeless. Bowthrusters use a lot of current, and will deplete a battery bank quite quickly, so they work best if the alternator can quickly recharge the batteries. Best bet if you must use a 24 volt thruster is to add a second 24 volt alternator to your engine plus a dedicated 24volt charger, but why do it? Get a 12 volt thruster, or if it is aleady installed, change the motor. Most makes use the same mechanical parts with either voltage of motor.

 

[lw395]

I think it depends on how much you expect to use the thruster. It will as has been pointed out, be running almost entirely from the batteries. So they need adequate capacity for your worst case berthing cock-up. I wouldn't do this for a sailing school boat or some other case where I expected to do repeated docking manoeuvres. But for the normal boat that wants a few 10second squirts of thruster twice a day, it could be a good approach. The batteries can be close to the thruster with short cables. Voltage difference in the long cables to the main supply are taken care of by the charger.
The key is probably the cranking ratings of the batteries, which may be stated as 'x minutes at 100amps' or something. You don't want to be approaching this limit.
And of course bear in mind, as the batteries age, the capacity will reduce so maybe you need some way of telling the batteries have had it, other than the thruster giving up at a John Cleese moment?

 

[nimbusgb]

There is a 12v Vetus motor for sale on Ebay for £175 right now. /forums/images/graemlins/smile.gif

 

[halcyon]

Connect batteries in series for use at 24 volt, parallel for charging at 12 volt from the alternator.

You could get a relay, assume you still can, that does it, was a rally car trick to start engine at 24 volt from 12 volt batteries. If you are not using it a lot, just use 3 isolator switches, 1 links batteries, other two connect in parallel with link isolator out.

Check your bow thruster amperage though.

Brian

 

[nimbusgb]

[ QUOTE ]
Connect batteries in series for use at 24 volt, parallel for charging at 12 volt from the alternator.

You could get a relay, assume you still can, that does it, was a rally car trick to start engine at 24 volt from 12 volt batteries. If you are not using it a lot, just use 3 isolator switches, 1 links batteries, other two connect in parallel with link isolator out.

Check your bow thruster amperage though.



[/ QUOTE ]

The problem with that is that your cant charge and use the thruster at the same time. So when your engine is running to manoeuvre you are running the thruster off the batteries only anyway. Unless of course you have an automatic circuit that chops and changes the circuit. The thruster is likely to be 1.5 kw or more so 100 amps plus, you need great big contactors for that, not usually rated for continuous operation.


. bit o

 

[sailinglegend420]

[ QUOTE ]
I have plans to install a 24v bow thruster with dedicated batteries but the rest of the boat is 12v

[/ QUOTE ]
We were looking at this too and concluded that a large 24 alternator was the answer, but you do need large cables to run the length of the boat to deliver 50 amps or more to give enough charge for when the boat comes back int the marina later in the day.

12 volt is not the answer if you have a large boat with high windage.

Are you looking at the Willdo water jet thruster here?

They also do the power take-off version which is hydraulically operated via the main engine. This looks like a better solution.