24 Volt to 12 Volt Conversion

[PAkev]

I humbly admit not being an electrical guru but will try to make my question as simple as possible:<br /><br />I will be putting a 74lb thrust 24V trolling motor on my 2000+ lb 19ft CC and want to keep the starting and acessory batteries independent. However I also need to power my electronics at 12V with down the road plans of perhaps a stereo, VHF, and power downriggers. The dealer is wiring trolling motor batteries in a series for 24V but what I am thinking of doing is somehow come off those connections with 12V power for accessories.<br /><br />I'm not really sure if my expectations are possible. Does someone make a power converter from 24V to 12V? Id really hate to draw from the cranking battery or add the weight of a fourth battery for acessories?<br /><br />Helpful advice appreciated.<br /><br />Kevin

 

[Franki]

Re: 24 Volt to 12 Volt Conversion

This refers to the two batteries running in series..<br /><br />run cables off just one of the batteries and you'll get 12 volts.. <br /><br />So the trolling motor runs off both batteries in series and the 12v stuff runs from only one of the series batteries.. <br /><br />Don't know if I am explainging myself well but we used to do it with trucks all the time...<br /><br />This is what I mean.. (just sketched this up.)<br />

<br /><br /> <br />hope that helps.. its always worked for us.<br /><br />rgds<br /><br />Franki

 

[snapperbait]

Re: 24 Volt to 12 Volt Conversion

Give Franki a gold star! excellent!

 

[18rabbit]

Re: 24 Volt to 12 Volt Conversion

Everything about Franki’s schematic looks like it will work. And it appeals to all of my brain cells…both of them...together. <br /><br />I would not do it. Here’s why:<br /><br />The batteries you will run in series are an investment. You will want to always purchase the same make/model at the same time. You also want the same load on the batteries whenever used so they experience the same wear-n-tear. If possible, recharge the way you discharged. When it comes time to replace the batteries, they both need to be replaced together and you will have gotten the maximum mileage from the pair IF their discharge profiles are identical.<br /><br />Using one battery to support an additional 12v system means the 24v source (two 12v bats) is unbalanced. That battery supporting the add’l load will always discharge lower and will experience a shorter useful life overall. How much depends on the 12v load. The other battery will still have some mileage left, but will need to be replaced anyway. Also, you cannot realize as much 24v A/Hr usage from the pair, either.<br /><br />We have two 24v systems on our boat. The 12v issue has raised its head a few times. Here are some other things to consider:<br /><br />Recharging- are you going to invest in a 12v and/or a 24v charging system? If you intend to use a single 12v charger, you need to be careful about how you hardwire any hookups to batteries run in series. The schematic, as shown, will not support a 12v charger without add’l consideration/equipment.<br /><br />4t Battery- Adding an add’l battery cannot be supported with a 24v charger. We have three 24v charging systems and I didn’t really want to mess with an add’l 12v charger. For us, adding an add’l battery dedicated to a 12v system would mean adding an add’l 12v charger as well.<br /><br />Electronics- a lot of marine electronics is available for 24v systems. You’ll be surprised. A bunch of it, including Furuno’s stuff, is self-sensing for voltage so you just plug it in and go. Other electronics (and pumps) you buy for the voltage you want. Everything we have onboard is 24v compatible without having to be something special…except the VHF. I wanted an ICOM radio and it was only available in a 12v model. So we are installing a 24v-to-12v converter. I figure that since I am there, I might as well add a small 12v distribution panel. We almost got away with it. <br /><br />Converters- yup, they’re there. Surepower makes a couple models with different amp ratings. I haven’t done much looking at what’s out there yet, mostly because I know they are there, but between Balmar, C-Charles, Newmar, Xantrex and a billion other marine electronic companies, there has to be more. I’m guessing a 10-amp converter will run me about $200.

 

[rickdb1boat]

Re: 24 Volt to 12 Volt Conversion

Maybe these articles will give you some ideas:<br /><br /> web page <br /><br /> web page 2

 

[kd6nem]

Re: 24 Volt to 12 Volt Conversion

It could be done, but would require a great deal of care in balancing the extra 12 volt loads between each of the batteries (and that assumes the useage is consistent, which is very iffy). This requires two seperate 12 volt circuits being run, which might have to be entirely redone later if anything else is added or changed. Could still be charged together as 24V. A lot of attention to detail would need to be maintained in useage as with the original hookup. I'm leaving a few details out; just saying that it could be done with some care. I would personally tend to not use any sort of converter unless the cost has dropped and efficiency increased a lot since I last played with these years ago. Depends on how you want to spend your money and effort. Rabbit is absolutely correct the two batteries must be drawn down the same amount for the batteries to last the same- they are a matched set and must be replaced together. I also agree with Rabbit's reasoning that 24V accessories greatly simplifies everything.

 

[PAkev]

Re: 24 Volt to 12 Volt Conversion

Hmm.....<br /><br />It looks like I have a lot more to think about.<br /><br />Dealer is suggesting going into the cranking battery for accessories and I guess, I could always jump from the deep cycle batteries in a pinch if the need should ever arise. Does this sound more practical and less complicated than special wiring and voltage regulators?<br /><br />Kevin

 

[18rabbit]

Re: 24 Volt to 12 Volt Conversion

If you go to the cranking battery to support your accessories you might want to take a look at a dual-use deep cycle for that application. A ‘normal’ starting battery could be a poor choice with even a moderate accessory load with something like a stereo.<br /><br />If you have a 12v VHF radio, you could hang just it off the starting battery without have to go with a dual use battery. The radio spends most of its life ‘listening’ using something nominal like .2-amp/hr. I would have gone this route but the starting system on our boat is also 24v.<br /><br />Start by looking at the accessories you want. Just about everything is either multi-voltage or available in a 24v version. The specs are usually online. You may not need to hang anything off the starting battery or need a voltage converter. I wouldn’t worry about the VHF either way.

 

[waterinthefuel]

Re: 24 Volt to 12 Volt Conversion

Can't you hook it up to where one 12 volt, 12 amp charger can charge them at the same time? I think it can be done, but one incorrect wire and you cook the charger.

 

[Franki]

Re: 24 Volt to 12 Volt Conversion

I fully agree with the comments about battery longevity.. I suppose that could be offset somewhat by rotating the batteries around each month.. <br />(or by rigging up the 12v side to switch from one battery to the other).<br /><br />That still leaves the charging system though..<br />If you pull the batteries out for charging individually on 12V then thats not an issue either. (or rig it so you can switch to charge each battery with 12v individually)<br /><br />I found something at an auto store the other day that I just had to have.. its a battery terminal with a wheel on it, screw the wheel down, the battery is connected, unscrew and its not.. and it was only about $5 bucks.. I have isolator switches and big relays but this things simplicity caught me and I had to have it.. (sorry, unrelated, but I kinda liked this thing.)<br /><br />Whether I'd do this or not depends on my 12v needs, if its a low 12v load, then I don't really see a problem, just rotate the batteries sometimes to equal the usage...<br />As I said before, that also depends on your charging scenario.<br /><br />regards<br /><br />Franki

 

[b_carione]

Re: 24 Volt to 12 Volt Conversion

frankie,<br /> I saw your diagram earlier for the 24v set-up. How would I wire the batteries for a 12v setup. I am planning on running 2 batteries for a 12v trolling motor and ff, and a separate 12v for a livewell

 

[JoeW]

Re: 24 Volt to 12 Volt Conversion

I have the same issue. I really don't feel like changing all of the systems on my boat from 12v to 24v, but I had to get a 24v trolling motor for my size boat. <br />It looks like I need 4 batteries <br />I guess that means I need two charging systems <br />Wow! That's a lot of weight.

 

[18rabbit]

Re: 24 Volt to 12 Volt Conversion

Joe – you are doing something wrong. Unless you are taking Krell amps (for your listening preasure ) with you out to sea, you probably don’t need 4 batteries. 1 for starting and a pair of deep cycles for that new TM… ?!?!?

 

[PAkev]

Re: 24 Volt to 12 Volt Conversion

After talking to several people, I am going with a dedicated cranking battery also powering my GPS/Sonar which is my only 12V accessory right now. The 2 12V deep cycles will be wired in a series for exclusively powering the TM. Once I get the boat on the water I will probably understand my previling needs a little better to determine if a 24V to 12V conversion is really neccessary. But for now, my insurance of getting stuck with a drained battery is a good pair of jumper cables that can be used to tap into one of the deep cycles in a pinch situation. <br /><br />Kevin

 

[JoeW]

Re: 24 Volt to 12 Volt Conversion

18rabbit,<br />What about all of the other 12volt accessories on the boat? As I understand it, I should not run these from my starting motor unless I like to paddle (which I don't) I can't run the accessories of of either of the two batteries dedicated to the trolling motor because that will produce unequal loads on these batteries. The only way around this that I can see is to have four batteries. <br />1 = starting<br />2 = 24v trolling motor<br />1 = all other 12v accessories (stereo etc).

 

[18rabbit]

Re: 24 Volt to 12 Volt Conversion

I really like simple...especially in things electrical. You are right about not creating un-equal loads on the 24v sys bats.<br /><br />1 = 12v starting and VHF<br />2 = 24v for TM + step-down converter for accessories.<br /><br />ShurPower step-down converters are around $120 for 5a or $240 for 15a at WM.<br />Analytic Systems step-down converter is $170 for 15a here at iBoats.<br /><br />http://www.iboats.com/mall/index.cgi?prod_id=14555&current_category= electric%3Econverter&cart_id=254753239

 

[JoeW]

Re: 24 Volt to 12 Volt Conversion

So do you power your instrument panel from the step-down converter as well?

 

[18rabbit]

Re: 24 Volt to 12 Volt Conversion

It’s really simple. A step-down converter takes 24v input and spits out 12v on the other side. (Can you guess what a step-up converter does? ) All your 12v accessories and wiring stay where they are. You do have to get a converter that matches the load…the total amps all the 12v stuff will draw, combined, plus 10%.<br /><br />Converters have heat sinks…that means there is heat involved…that means inefficiency to some degree. Inputting 1a @ 24v will not yield 2a @ 12v…you get something more like 1.8a @ 12v. About 10% is lost. It’s not that big a deal if you consider the amps used by all 12v accessories during a day’s boating…if you use 40a now, converted you would use 44a.