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Old 20-04-2016, 20:04   #1
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DC-DC Converters 24V to 12V

I am installing a 24V LiFePo battery bank on a 12V boat. Using a 5KW Inverter and wanted to use 24V for this application. I've got 24V alternators as well. So I need to convert to 12V to power general lighting, instruments, engine controls, hoist (Tender Davit) and windless. The largest single draw is the windless at 1500watt (measured at about 120 amps). Never use Davit and windless simultaneously, but want to leave all of the instruments, radar, MFD's on when running the windless.

Considering two Victron Orion 24/12-70s in parallel or an RM VR120SW rated at 1620 Watts. This will be used with a Icom M802. The VR120SW has pretty good spec's and publishes ripple and other stats that the Victron doesn't.

Anyone used either of these converters and/or have any comments?

Thanks to all of you who donate your time to share with all of us.

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Old 20-04-2016, 20:39   #2
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Re: DC-DC Converters 24V to 12V

No personal experience with Victron- but nothing is infallable .
My practice,when installing converters for customers,was to tap the battery at 12V & feed this to one side of a Bat,1,2 swx. Converter 12V out was fed to the other side. Label swx as "Emerg. 12V" & set it to converter position.
If converter fails,throw swx to Emerg. & you still have 12V-for VHF,etc.

Cheers/ Len
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Old 20-04-2016, 21:04   #3
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Re: DC-DC Converters 24V to 12V

you should change the windlass, davit, bigger loads to 24v. I would not down convert the whole boat that is crazy and poor planning.


the engine controls should be off the existing 12v engine battery not your house battery


if you are stuck with this now I would put in a 12v bank with a 24-12v charger. one that will charge the 12v bank even if the 24v one isn't charging. (some are voltage controlled) the battery will handle of current bursts of the windlass etc.
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Old 20-04-2016, 22:17   #4
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DC-DC Converters 24V to 12V

I agree, have to change the big consumers to 24 v. Lots of boats run 12 and 24 off different batteries and two alternators for 12 and 24 so can still keep 12 for the smaller things.


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Old 21-04-2016, 00:57   #5
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Re: DC-DC Converters 24V to 12V

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Originally Posted by stillbuilding View Post
I agree, have to change the big consumers to 24 v. Lots of boats run 12 and 24 off different batteries and two alternators for 12 and 24 so can still keep 12 for the smaller things.
I too agree that the windlass should be modified for 24V. On Lofrans windlass you can buy a 24V @ 1500W motor for about 500 EUR. About the same I suppose for your davits winch. Hopefully your autopilot has a 12V/24V input. You don't say about your engine starter but I suppose it's 24V already, like the alternator. I do not not see the point of adding a 12V alternator.

From there you could probably use the smaller Orion 24/12-25A which is more efficient (96%) and is fanless ! I would trust this one more than the bigger 70A model which is fan assisted and less efficient (92%). From the specs those Orion are "suitable to buffer charge a battery", so you can put a small 12V batt in between the Orion and the 12V network if you feel you might reach or exceed 25A from time to time.

As for redundancy in case the 24/12 converter fails you might use a small 12V charger like the IP65 from victron to be plugged in your 110/230VAC, or a spare Orion 24/12 converter as the 25A model is quite cost effective at less than 100 EUR.

Those Orion 24/12-25 can be paralleled so you might as well use two of them (+ one spare) and no 12V battery instead of <one 24/12 converter + 12V battery>.

I should add that this is only theoretical as I have never done such a setup but I am planning myself to convert a 12V boat to 24V so I would be glad to know who it works for you
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Old 21-04-2016, 02:09   #6
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Re: DC-DC Converters 24V to 12V

You've gotten good advice.

Having a 24v system and converting to 12v to drive a windlass is crazy. Bit the bullet and convert the main things to 24v -- you'll be glad you did, as any heavy consumers will work better on 24v.

Lighting should also be 24v. Nearly all modern LED bulb units now work on any voltage from 9v to 30v.

For anything else which is too much trouble, use droppers. There are various makers of these, including Victron. But don't drive heavy consumers like windlasses or davits through droppers.
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Old 21-04-2016, 05:26   #7
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Re: DC-DC Converters 24V to 12V

Thanks for the reply.

I realized early on this was not the ideal situation, but considered the following:
1.If I could find the 1500W motor for 500Eur, I'd be all in. Where do you suggest? I'll be in Italy in June and the windless is a Lofrans, Unfortunately all I've found is $1,500 here in the US. While I would love to go all 24V the truth of the matter is that the windless works just fine as it is
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Old 21-04-2016, 05:33   #8
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Re: DC-DC Converters 24V to 12V

Yes those are good options in an emergency. Nice thing about doing my own system is it is much easier to work around equipment failures.
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Old 21-04-2016, 05:36   #9
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Re: DC-DC Converters 24V to 12V

Hi John

Try SVB:

https://www.svb24.com/en/lofrans-electric-motor.html

The other option is an auto electrical shop. They are accustomed to rewinding starter motors. Windlass motors are very similar.

I think changing the windlass voltage would be sensible.

A 24/12v converter is fine (and quite cheap) for lower current devices.
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Old 21-04-2016, 05:39   #10
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Re: DC-DC Converters 24V to 12V

Would it be practical to install a good 12V battery for windlass & davit & recharge the bat(s) from 24V? Those two items are only used for short periods.
Operate other 12V eqpt. (VHF,etc) thru a converter.
Less expensive than changing motors,etc ?

Edit: Just re read OP. You are putting in a 5KW inverter? There is your AC charging source for a 12V battery using a bat. charger.
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Old 21-04-2016, 06:19   #11
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Re: DC-DC Converters 24V to 12V

I hesitate to bring this up, but many, many 6V tractors etc, Ford's in particular were converted from 6V to 12V by changing the coil and replacing the generator with an alternator, and a couple of light bulbs.
Starter worked fine off of 12V, we had one my whole child hood.
Then there is also a "fast start" kit for turbine aircraft that takes the dual 24V batteries and connects them in series to 48V for faster starting, and although the starter-generator is 24V, it actually has a shorter run time and runs cooler off of the higher voltage.
www.airrepairinc.com/Fast-Start.pdf

I wouldn't be surprised if your windlass ran just fine off of 24V, going to run faster of course.
Worst case, it won't and you have to replace the motor.
You will still need to convert 24 to 12, but it's a lot cheaper if you don't have to do that high amperage conversion
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Old 21-04-2016, 06:36   #12
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Re: DC-DC Converters 24V to 12V

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Originally Posted by deblen View Post
Would it be practical to install a good 12V battery for windlass & davit & recharge the bat(s) from 24V? Those two items are only used for short periods.
Operate other 12V eqpt. (VHF,etc) thru a converter.
Less expensive than changing motors,etc ?
Let's do the math: say you use the windlass for 2 minutes at full power: 1500W@12V makes about 125A, which in turn makes 125Ah if used for one hour, which only makes about 4.2Ah when used for 2 minutes. Add the davits for 2 times one minute per day and that's about 10 to 15 Ah @ 12V per day total. That's not so much and a 60Ah batt could handle that.

Only problem is 125A is about a 2C discharge rate for a 60Ah battery. A bit less if you take into account the 25A or more from the 24-12V converter. Still I am not sure how long the battery will last. Maybe some forum expert could chime in and explain which battery size would be appropriate for reasonable life time expectancy. Interesting !

Quote:
Originally Posted by deblen
Edit: Just re read OP. You are putting in a 5KW inverter? There is your AC charging source for a 12V battery using a bat. charger.
And you might as well read the rest of the thread
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Old 21-04-2016, 06:52   #13
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Re: DC-DC Converters 24V to 12V

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I wouldn't be surprised if your windlass ran just fine off of 24V, going to run faster of course.
I guess you are right but I suspect the mechanical parts of the 1500W windlass will not like being fed with 3000W of power ... unless you can current-limit to about 60A but I don't know how you would do that.
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Old 21-04-2016, 07:02   #14
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Re: DC-DC Converters 24V to 12V

I don't know about your Windlass, but mine has a clutch that prevents overload
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Old 21-04-2016, 07:06   #15
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Re: DC-DC Converters 24V to 12V

24v makes sense for the windlass, bite the bullet... lots of advantages of higher voltage on boats... as for converters, we always use the Newmar models and have never seen a failure. They provide a regulated 13.8v out from 20-50vdc in. The model we usually install is the 30amp one (surge to 35). Many older Chris Craft and Hatteras models use 32volt systems (like railroads did) and these converters handle the new 12v electronics/etc.
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