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Old 19-11-2010, 02:29   #1
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24vdc - Newbie Needs Help ! Funny, too !

Hi everybody,
I am the reluctant, undesired owner / builder of a 15 meter wood hulled MONSTER of a boat..... Long story so lets get to the meat of it.....
I have a 24 volt alternator on my ANCIENT yanmar 6 cylinder diesel... Now, lets presume I know NOTHING about boats...
The boat is used for scuba diving....it is generally going to be run during the day time.....
I have minimal electrical requirements, VHF, GPS, a few small marker lights, a couple of of small deck lights, about five other assorted lights, all lighting requirements would be met by 12 V car tail light bulbs...
A TINY amount of 220v 50hz is needed...charge camera batteries, maybe run a laptop...
Well I have 2 HUGE !!!!!! 12 VDC batteries set up in series to provide the starter with the 24 volts it needs....
There in lies my problem, how do I tap into the 24 v loop to get 12v out ???
I have seen a couple of 24 to 12 volt converters.....Is that my only solution ???? They are quite small and not cheap...
For the 220 a small inverter is not a problem, if I can find one in the country....everybody has 12VDC > 220VAC, 24VDC is another story, please note I am in the third world, so sourcing ANYTHING locally is insane..
I need it yesterday for the "electrician" who showed up with 20 amp breakers.....for 220VAC !!!!!! To put in my hoped for 12 v system....Yes IT IS TRUE !!!!!! lets see, how many amps can I run through a number 24 wire... He may know something I do not....but there is a relationship between voltage and amperage.....all else being equal...as the volts go down the amps go up....right ? (rhetorical question). This guy wanted to wire my fuse panel from the batteries with 22 gauge wire !!! So obviously there is no local knowledge...
In fact I cannot find ANYWHERE in the COUNTRY, an automatic bilge pump !!!!!!
The locals put a tee in the sea water intake, close the valve to the sea, open the valve to a hose and use the ENGINE water pump to drain the bilge !!! I cannot make this stuff up, it is REAL !!!!!!

Best solution for me, is to some how tap the 24V loop, get out 12V, then invert the small amount of 220VAC that I need....
Help please !!!!!

Thanks everybody !
Larry
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Old 19-11-2010, 06:03   #2
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A couple solutions:

1) The "proper" solution to get 12v is to go with a 24v-to-12v DC-DC converter. Depending on how much 12v capacity you need, these converters cost anywhere between $200 and $1000 USD.

2) A "hack" solution would be to split-tap your 24VDC battery bank. Since it is made from two 12v batteries, simply attach your 12v + and - to one of the batteries. If you do this KEEP THE 12v GROUND WIRE SEPARATE FROM ANY EXISTING 24v GROUND WIRE. The reason: depending on which battery you tap, you may inadvertently "parallel" the two batteries, which would not be good. Consequences of wiring things this way is you will create charging problems for the 24v bank as a whole and the lifespan of both batteries could be reduced.

I would only do #2 if I was in a pinch and really needed 12v as a TEMPORARY solution.

#1 is the best solution. Note, there are many makers of "non-marine" DC-DC converters on the internet, which should be cheaper than the marine types. The critical thing is to match the current requirements of your 220v inverter.
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Old 19-11-2010, 06:14   #3
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Quote:
Originally Posted by westsail42 View Post
A couple solutions:

1) The "proper" solution to get 12v is to go with a 24v-to-12v DC-DC converter. Depending on how much 12v capacity you need, these converters cost anywhere between $200 and $1000 USD.

2) A "hack" solution would be to split-tap your 24VDC battery bank. Since it is made from two 12v batteries, simply attach your 12v + and - to one of the batteries. If you do this KEEP THE 12v GROUND WIRE SEPARATE FROM ANY EXISTING 24v GROUND WIRE. The reason: depending on which battery you tap, you may inadvertently "parallel" the two batteries, which would not be good. Consequences of wiring things this way is you will create charging problems for the 24v bank as a whole and the lifespan of both batteries could be reduced.

I would only do #2 if I was in a pinch and really needed 12v as a TEMPORARY solution.

#1 is the best solution. Note, there are many makers of "non-marine" DC-DC converters on the internet, which should be cheaper than the marine types. The critical thing is to match the current requirements of your 220v inverter.

I completely agree with you in this case, in light of the "desperate" nature of the OP's plea.
But I have to say, I think you are a brave man, to come on THIS forum and post that advice.
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Old 19-11-2010, 06:31   #4
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Being a lazy non tech sorta guy I'd not bother with all this complex stuff.... and possible system screw-ups....
Just buy a 12v car battery and a 20w solar panel to keep it topped and dedicate it to your whatevers.....
I do this for my Tillerpilot.... its own dedicated battery seperate from anything else on the boat.... ya gorra look afta de crew..
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Old 19-11-2010, 06:38   #5
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Quote:
Originally Posted by Blue Stocking View Post
I completely agree with you in this case, in light of the "desperate" nature of the OP's plea.
But I have to say, I think you are a brave man, to come on THIS forum and post that advice.
Ha! Yeah, I would NEVER do the #2 option (did I not provide enough disclaimers and warnings??? ). But he did sound desperate!

But boatman61 makes a good suggestion. A dedicated 12v battery, provided you can keep it charged to enough to power your inverter loads. Maybe add a second 12v alternator?
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Old 19-11-2010, 06:43   #6
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Why not put on a 2nd alternator (12v) and a separate battery. Given your minimal needs you can use any car alternator and battery - look for a wreck. Don't worry about fancy external charging regulators. Think "car".

Most Yanmar's will take a 2nd alternator quite easily. You'll find bolt holes for a bracket and arm and a place to mount a pulley on the front of the crankshaft. Finding the a pulley will be the toughest part. Find a truck or agriculture equipment place. Since it doesn't need to be pretty, you can probably make up the brackets from scrap.

Carl
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Old 19-11-2010, 06:48   #7
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Before going off looking for the alternator, try to understand what kind of alternator mount the Yanmar is expecting. There are 3 or 4 types. It will be much easier if you have the right mount type.
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Old 19-11-2010, 06:48   #8
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A second(3rd) battery is his bet bet. To prevent the ground problem. Hookup as follows... Ground---------Battery1--------Battery2----24volts. Tap off of battery 1 for 12volts. You really dont want to mess with the starter batteries though. For the loads (laptop camera) a small portable inverter with a single 12volt deepcycle and seperate charger would be the optimum solution.
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Old 19-11-2010, 09:08   #9
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Great !!!!!

Thanks guys !!!!!!!!

Is it an " ideal " solution to the problem ? That is my impression, as I would just be running a car electrical system.
The second alternator was my choice of systems as well. Though finding room for it will not be easy, the do have a miracle tool here...the BFH.

From an advertisement...
"The BIG F****** hammer is a miracle instrument specially designed, engineered and built to solve EVERY problem known to man, need a torque wrench ? 3 smacks on your open end wrench with our medium size version = 50 ft LBs, pesky mosquitos ? Use the large version, fight with the wife ? Use the titanium handle super solution size !"

I was thinking of system #2,....but it made my gut do some funny things...If I remotely thought of it has the solution, it would all ready be done....instead I posted here...

I was indeed thinking CAR !... Exactly.....pulley? ....NO PROBLEM.....just have to know the right diameter, as the motor idles at like 500 r.p.m. and the top speed is 1600, at the crank..... Shop time here to make a pulley is about $1 an hour....
Tomorrow, I will check the pulley diameter on the engine, get a big alternator, rectifier from a car, and bolt that up.
I love this solution in that I can NEVER accidentally drain down the starter batteries....,
There is the other option.....bolt one HUGE generator to the PTO on the front !!!! Have a look !!! By the way....that motor is 34 BHP, but 350 ft lbs of torque !!!! It weighs like 1,500 Lbs !!!!
Any suggestion where to mount the alternator ? Or just pop the belt cover and hope I get lucky ?....Tomorrow I will post pictures of the $30 steering gear.....REBAR...threaded and welded.... Mind numbing !!!!
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Old 19-11-2010, 09:19   #10
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I think if you're going to add a 12V alternator why not just convert the whole thing to 12V and be done with it. I can't see much savings in this case by running two diferent voltage system. I can see big trouble down the line with wiring confuson though.
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Old 19-11-2010, 09:41   #11
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Thanks for your reply....

Amomg The two 24> 12 I could find was this one...
.24 volt to 12 volt DC/DC converters (fully regulated) from 100 to 700 Watts non-isolated and isolated..
While cheap at $220m it does tap into the starter batteries....which of course I requested, the problem is the price will double with air freight, and it will take 3-4 weeks to clear customs.....Others have posted a second alternator option which I think is excellent....and saves the three week wait at customs !

Quote:
Originally Posted by westsail42 View Post
A couple solutions:

1) The "proper" solution to get 12v is to go with a 24v-to-12v DC-DC converter. Depending on how much 12v capacity you need, these converters cost anywhere between $200 and $1000 USD.

2) A "hack" solution would be to split-tap your 24VDC battery bank. Since it is made from two 12v batteries, simply attach your 12v + and - to one of the batteries. If you do this KEEP THE 12v GROUND WIRE SEPARATE FROM ANY EXISTING 24v GROUND WIRE. The reason: depending on which battery you tap, you may inadvertently "parallel" the two batteries, which would not be good. Consequences of wiring things this way is you will create charging problems for the 24v bank as a whole and the lifespan of both batteries could be reduced.

I would only do #2 if I was in a pinch and really needed 12v as a TEMPORARY solution.

#1 is the best solution. Note, there are many makers of "non-marine" DC-DC converters on the internet, which should be cheaper than the marine types. The critical thing is to match the current requirements of your 220v inverter.
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Old 19-11-2010, 09:52   #12
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Hi Boat man...Thx for the post...

Solar panel......third world, yes they are spottily available....but the big issue about solar, is....ugly....The boat does have a 14 m X 4m flat roof..... So can I install so it is only just slightly off the roof deck ? or does it have to be pitched up ?
THx
Larry

Quote:
Originally Posted by boatman61 View Post
Being a lazy non tech sorta guy I'd not bother with all this complex stuff.... and possible system screw-ups....
Just buy a 12v car battery and a 20w solar panel to keep it topped and dedicate it to your whatevers.....
I do this for my Tillerpilot.... its own dedicated battery seperate from anything else on the boat.... ya gorra look afta de crew..
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Old 19-11-2010, 10:06   #13
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Hi Bill

This is obviously the simplest solution to the problem....
But seems many posters do not like it...unless I am not understanding clearly. can you please come back to the post and have a look at the new info ?
Thanks
Larry

Quote:
Originally Posted by capn_billl View Post
A second(3rd) battery is his bet bet. To prevent the ground problem. Hookup as follows... Ground---------Battery1--------Battery2----24volts. Tap off of battery 1 for 12volts. You really dont want to mess with the starter batteries though. For the loads (laptop camera) a small portable inverter with a single 12volt deepcycle and seperate charger would be the optimum solution.
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Old 19-11-2010, 10:11   #14
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A good size truck dealer should stock, or be able to direct you to a local 24-12v converter source.
Many trucks from the Pacific rim are 24v, and I often fit them for 12v cell phones, stereos and electric door locks.
The U.S company Transpo build a unit with a single 12v 30a output, or a unit with 5 outputs, ranging from 2 to 5amps to allow U.S. trailers to operate 12v lights (indicators, brakes, running and back-up) from the truck's circuits.
Hope this helps.
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Old 19-11-2010, 10:28   #15
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Larry,

some options:

I have a Newmar 24-12v converter for my SSB, 30A capacity, cost about $150.

12v Solar panels as someone else suggested.

Second alternator - could be your best option if getting spares is an issue where you are, look for two identical in the breakers yard.

You should also consider your batteries. The batteries you have already are likely to have high cranking amps to start your engine, but will probably not tolerate being drained by much more than 5%, and if you tap into one of them for 12v, the imbalance will kill them both in no time, as will leaving the lights on. If the engine is running most of the time its less of an issue, otherwise you need to keep the 12v equipment separate
from the starting batteries. Try and find a deep cycle battery for your 12v circuit if you can, you can discharge it to 50% and it will charge right back up again. Golf cart batteries are a good place to look, although you will need to combine more than one to get 12v.
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