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  1. #1
    Join Date
    Nov 2002
    Location
    Colwell Bay
    Posts
    5,637

    Default 24v boat but 12v bog.

    Ahoy!

    My boat is 24v, 2 banks of 12v batteries, single engine with alternator and a split charge relay.

    I bought the 12v electric loo that Force 4 sell for £199, twas a preference of the crew.

    Realising that I needed 12v for the loo, I rummaged in my shed of boat junk and found a 24v to 12 converter, ebay chinese finest, rated at a max of 20amp on the 12v output, the bog draws 17amps.



    Wired it all into place and pressed the button, all I got was a series of clicks, but whirring and flushing.

    So tonight I ran a temporary wire direct from the 12v link between the batteries to the bog and it spurted noisily into life. Rejoice!

    Clearly the chinese volts dropper not able to deliver 20 amps.

    It'll need an isolator and a fuse, given its for shorts bursts very rarely, I think its ok to pull off one battery? Rather than buy a better voltage converter? Any reason its not ok to pull from one battery?

  2. #2
    Join Date
    Mar 2015
    Location
    Isle of Eigg
    Posts
    7,205

    Default Re: 24v boat but 12v bog.

    Quote Originally Posted by burgundyben View Post
    Ahoy!

    My boat is 24v, 2 banks of 12v batteries, single engine with alternator and a split charge relay.

    I bought the 12v electric loo that Force 4 sell for £199, twas a preference of the crew.

    Realising that I needed 12v for the loo, I rummaged in my shed of boat junk and found a 24v to 12 converter, ebay chinese finest, rated at a max of 20amp on the 12v output, the bog draws 17amps.



    Wired it all into place and pressed the button, all I got was a series of clicks, but whirring and flushing.

    So tonight I ran a temporary wire direct from the 12v link between the batteries to the bog and it spurted noisily into life. Rejoice!

    Clearly the chinese volts dropper not able to deliver 20 amps.

    It'll need an isolator and a fuse, given its for shorts bursts very rarely, I think its ok to pull off one battery? Rather than buy a better voltage converter? Any reason its not ok to pull from one battery?
    The problem is that the bog will draw a shed load more than 20A as it starts. The inverter simply cannot supply the inrush current for the bog.
    Choices
    As you say, a beefier converter, but do find out the start-up current. Or perhaps a small 12V battery fed from the converter.

    Running of one half of a 24V battery might not be a great idea. You rely on one 12V managing to charge off the float charge for the other. Usually either one goes completely flat or the other boils... or both!
    FUCTIFANO

  3. #3
    Join Date
    Sep 2001
    Location
    Me - Zumerzet Boat - Wareham
    Posts
    12,153

    Default Re: 24v boat but 12v bog.

    Quote Originally Posted by Lon nan Gruagach View Post
    The problem is that the bog will draw a shed load more than 20A as it starts.
    Also a motor is an inductive load.
    MontyMariner.co.uk
    Facilitated by AWESEM WP Agency

  4. #4
    Join Date
    Jan 2012
    Location
    South Coast
    Posts
    5,137

    Default Re: 24v boat but 12v bog.

    Whereas it is not such a good idea to run a regular service item from a mid connection on the 12- 12 v series link, an occasional use item like the loo is in practice hardly going to be that that big a deal. I can't see it causing an issue.
    Interested in Corvettes PM me for details of the Corvette Motorboat Association

  5. #5
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,432

    Default Re: 24v boat but 12v bog.

    Quote Originally Posted by burgundyben View Post
    Ahoy!

    My boat is 24v, 2 banks of 12v batteries, single engine with alternator and a split charge relay.

    I bought the 12v electric loo that Force 4 sell for £199, twas a preference of the crew.




    Wired it all into place and pressed the button, all I got was a series of clicks, but whirring and flushing.

    I think its ok to pull off one battery? Rather than buy a better voltage converter? Any reason its not ok to pull from one battery?
    Not the best of ideas because its partner will always be overcharged to get this one charged

    Other ideas

    Investigate the possibility that a 24 volt Jabsco toilet motor will fit ( only costs £191)

    24 V to 12 V Battery to battery charger and a small 12 V deep cycle battery (£250 + the price of the battery)

    Sell it on ebay and buy a 24 V jabsco

  6. #6
    Join Date
    Sep 2001
    Location
    Me - Zumerzet Boat - Wareham
    Posts
    12,153

    Default Re: 24v boat but 12v bog.

    Quote Originally Posted by VicS View Post
    Investigate the possibility that a 24 volt Jabsco toilet motor will fit ( only costs £191)

    Sell it on ebay and buy a 24 V jabsco
    When my 24v Jabsco loo motor packed in, it was cheaper to buy a complete new loo than just the motor and macerator unit !
    MontyMariner.co.uk
    Facilitated by AWESEM WP Agency

  7. #7
    Join Date
    Jul 2003
    Location
    West Australia
    Posts
    11,615

    Default Re: 24v boat but 12v bog.

    You might try one or more of the really large electrolytic capacitors across the output of the converter. Like these.https://www.jaycar.com.au/4700uf-25v...citor/p/RE6244 You can use as many as necessary in parallel to give the required assist to manage the inrush motor current. Might be simple fix or a waste of a bit of money on capacitors. Make sure they are rated at 25volts.
    However do check the actual voltage out of the converter. In many cases they deliver more like 13.75 volts to emulate a 12v battery on charge. This voltage may be suitable to perform the role of 24 to 12v btob charger. Then all you need is an additional 12v battery. Perhaps an old or new car type battery. This will then easily provide the inrush current for the motor. You may wish to go further with the 12v battery to form a second isolated service battery system for radio electronics or even a fridge. ol'will
    Last edited by William_H; 08-07-19 at 00:31.

  8. #8
    Join Date
    Nov 2002
    Location
    Colwell Bay
    Posts
    5,637

    Default Re: 24v boat but 12v bog.

    Thanks all.

    Its likely to be 20amps, for 5 seconds, 4 times a week. Its tiny.

    I think for now I'll leave as it is, fit an isolator and fuse, then when I tackle some of the other electrical jobs I may well put in a 12v battery charged from the 24v.

  9. #9
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    7,705

    Default Re: 24v boat but 12v bog.

    Quote Originally Posted by burgundyben View Post
    Thanks all.

    Its likely to be 20amps, for 5 seconds, 4 times a week. Its tiny.

    I think for now I'll leave as it is, fit an isolator and fuse, then when I tackle some of the other electrical jobs I may well put in a 12v battery charged from the 24v.
    Typical PBO electrical thread, completely out of proportion to the "problem". All you need to do is fit a decent, suitably rated, DC-DC converter. Just about all big mobos are primarily 24v, with a 12v circuit, as are most of the commercial boats i work on.

    https://www.es-store.co.uk/product_l...3&show_menu=26
    Rainbow Marine.
    www.rainbowmarine.co.uk

  10. #10
    Join Date
    Nov 2002
    Location
    Colwell Bay
    Posts
    5,637

    Default Re: 24v boat but 12v bog.

    Quote Originally Posted by PaulRainbow View Post
    Typical PBO electrical thread, completely out of proportion to the "problem". All you need to do is fit a decent, suitably rated, DC-DC converter. Just about all big mobos are primarily 24v, with a 12v circuit, as are most of the commercial boats i work on.

    https://www.es-store.co.uk/product_l...3&show_menu=26

    but a DC-DC converter that would provide enough juice for the inrush current would be quite costly no?

    I have 2 DC-DC converters to provide for the various 12v stuff like VHF and AIS and Radar etc.

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