24v/12v Converter for Windlass

I got a great deal on some 24v equipment, and since I hadn’t totally committed to 12v, I elected to purchase the gear and go the 24v route. My problem is that I also have a new 12v anchor windlass that I would like to utilize. I’ve researched the various equalizer / converter options but am unclear on one point. Maybe someone could help me figure this out.
My thought is to run 24v cables to the bow that are sized to handle a 24v thruster and an eventual 24v windlass (after my 12v windlass dies or I trade it for a 24v unit). In the meantime, I’d terminate the windlass cables at a 24v/12v converter that feeds an auxiliary 12v battery (ies), which in turn power the windlass.
The 12v windlass is rated at 1500w/ 125 amp. A 100 amp converter (or equalizer) is north of $600 which I’m not excited about. My questions are:

1. If this was a strictly 12v system with the alternator charging the battery up front and the windlass is drawing 125amps, is the current between the alternator and the battery 125 amps, or does the battery act as a buffer? (I would always size the cables for the entire load).

2. If I use a smaller 24v/12v converter (30amp?)between the 24v batteries and 12v bank, and the windlass is pulling directly off the battery, how much current is in the line between the 24v bank and the converter?

3. If the windlass is drawing 125 amps from the 12v bank, will I fry the 30 amp converter?

Regards,
SeaJay

 

what voltage is the alternator on the engine? if its 24v why not fit a second alternator and have a 12v sub system for the winch....
what is the voltage of your main battery bank ? what is the voltage of your starting battery/starter motor ??
why dont you just power it off the "12v aux battery " ..how are you charging that at present?

 

SeaJay,

"after my 12v windlass dies"

There is not much chance that you will destroy the 12VDC anchor winch in a hurry (ran at 12VDC of course), they are very reliable.

Put two 12V batteries at the bow thruster (in series for the 24V) and just use one of them for the anchor winch (12V), problem solved. Swap the batteries say, twice a year to load them equally (as such) and they will be OK.

 

That's not a very good idea Landlubber.

The 12v battery connected to the 24 volt source will get badly over-charged and the second battery will not get recharged. The amount of current that will pass through a battery (at a given voltage) depends on the state of the battery's charge. The 'top' battery will also be subjected to MUCH more voltage than it should when the winch is running.

The best approach would be to find a 24v/12v converter that is over-current protected and use that to charge the 12v battery and let it overload when the winch is running.

There are definite advantages to a dual system, like being able to use inexpensive 12v automotive accessories.

 

Landlubber - "or I trade it for a 24v unit"

Pistnbroke - I'm installing a 24v alternator for the house bank and a 12v alternator for the starter battery. My issue isn't so much how to charge the forward batteries but rather, how much current is trying to pass through the converter if it is placed before the 12v windlass battery. I would think that the batteries absorption rate would naturally limit the current through the converter...but then again, this is just an uneducated guess.

DianneB - you are on the right track as to what I'm trying to accomplish. The use of a 12v windlass in this situation is completely contrary to why you set up a dual system in the first place but it is what I am facing. How would you size the overcurrent converter? I wasn't sure they came with over charge protection, but that would certainly take care of one issue.

Now that you folks are sparking my thinking process, I suppose the proper question to ask is can a battery absorb at its maximum discharge rate while being discharged? In other words, if the windlass is drawing 125 amps, is the alternator supplying 125 amps at the same time?

 

Dianne,

Yes and no, the fact is the engine is running when the anchor winch is being used, and the run time is not large, so the actual battery drain is minimal.......I am not recommending that the system I proposed be a usual installation, I was trying to solve the OP quest for a solution that will not destroy the bank, more than a recommendation for installation.

By switching the leads every 6 months, there will be very little reduction in battery life in the real world.

 

The technical specifications for a converter should mention any limitations on over-current.

Once the winch comes on, the converter will try to carry the entire load from the winch (because the battery voltage will drop under load) so it is important that it is current-limited (which they all should be). That will let the voltage drop to what the battery can deliver at that load.

That being the case, the converter only needs to provide an amp or two to recharge the battery between uses. That should make the converter inexpensive.

The other alternative would be to use a single pole (or double pole) double throw switch where in the off position the converter is connected to the battery and in the on position the switch activates the winch. That way the converter never sees the winch load. Simple and cheap!

 

Dianne - I'll check the converter specs carefully. Using a smaller one to just re-charge the 12v battery was what I had in mind. As long as I wasn't damaging it by drawing heavily on the battery then I think I would be ok. Your switch suggestion has merit as well. Thanks.

 

Conversely this is my problem at the moment. I have a 24v solar system but found most of the equipment I can purchase runs on 12v voltage. I have to run most of them through the converter which would mean a 50% loss. Converters are usually series pass transistors. The transistors "absorves" half the power. To increase power absorption, I need higher power converters and power transistors are expensive.

Two 12v batteries are in series. I cannot tap on the 12v batt alone to have a 12v supply as this is bad practice.

 

god I feel ill ...until you answer the questins re engine alternator voltage etc I asked earlier all the answers are total speculation .....

 

Seajay,

Just took a look at electric windlass specs. A typical 40 feet/min windlass will consume only 14A at freeload but whoah! It will consume 110A at stalled condition. What is that 125A load you have there, stalled or free load?

Rx

 

These do not have the efficiency problem you are concerned with but are not inexpensive:

http://www.dan-marc.com/34-6560c.html

 

Pistnbroke - 24 v high output alternator for house bank, smaller 12v alternator for starter battery. I didn't want to use the starter battery for the windlass but I think I've found the solution. I spoke with Balmar and they recommended the Blue Sea ACR.

http://www.starmarinedepot.com/Blue Sea 7610 SI-Series Automatic Charging Relay.html

I think this will do the trick. I can charge both the windlass battery and starter battery from the 12v alternator or the shore charger but keep them isolated under load. Also, I'll only have relatively light gauge wiring forward to the windlass battery.

rxcomposite - There is some confusion in your statement. "between the 24v batteries and the 12v bank". I thought you said you have a bank 1 (12V starting batteries) and bank 2 (24v house batteries) which are entirely separate? -

I would actually have three "banks"...1) 24v house bank 2) 12v starter battery 3) 12v windlass bank. I do want to keep the starter battery isolated from the windlass bank. Again, I think the Blue Sea ACR will do what I need for about $70.

Thanks everyone for the input

 

Thanks Bglad. They are expensive.

I thought of using solar for the free energy but I am spending more for the mismatch and throwing half of the "free power" as waste.

I will concentrate on finding 24v powered loads. Problem is I have four 12V computer grade inverters here. It will take a long time before all of them burns out.

 

why not charge 2 batteries in series for 24v. Also wire them in parallel for 12v.