Main Starter Motor Feed 12v Direct From Battery

I have an engine with a 24 volt starter and the rest of the boat is 12 volt. Thr previous owner has only 12 volts on the starter. This does not turn the engine adequately. To add to the confusion, I have a freedom 20 charger onboard. The issue is that I need to be able to start the engine (24 v) and charge the batteries and run the house (12 v), and be able to charge them. I have to admit, this is a challenge to me. Anyone that has this setup on their boat and has wiring advice would be very appreciated.

Kevin

Probably two banks of batteries to accomplish this? One bank, run in series, would give you 24 (2, 12's in series). I think we need a little more information.

If you have a separate house battery and starter battery, you can wire them through a small relay to actuate a set of solenoids in a double pole double throw arrangement that series the batteries for starting purposes. The system must be isolated from other systems, but that's easy enough to do with the relays. If one battery is larger than the other then use it as the "lower" battery in the series arrangement and run the rest of your systems normally. You should have all electronics turned off when starting an engine at all times, using this arrangement or not......a few bucks of parts......
Injuneering time $375 per hour or any portion thereof...YMMV

07:35 PM

A series-parallel switch is what's needed but it is much simpler and probably less expensive to buy a new 12V starter.
The series parallel switch is old school (40's-50's), and can be a pita - starters have improved quite a bit over the years and I rarely see this 12v/24v set-up any more. Larger engines (20+ liters) and extreme cold weather (Alaska) can sometimes warrant this combo. edit to add image

Schematic here
*note the switching current capability - a starter can draw over 250 amps

Have you looked into the 12 volt starter availability? Marine starters are expensive alright, but the simplicity of a starter over a relay set-up would be worth it. Keeping it simple seems like the way to go.

I haven't checked into a 12 volt for this engine. It is a very old mercedes om314. They came with the 24volt starter. I'm not sure if a 12v is available. I will investigate all possibilities of course. My thought is that at one time this must have been set up correctly. The other thing is whether the charger can be set up to charge all of the batteries.

I had the same problem only to discover the starter worked fine with a decent battery. This was on an old Gardner 4lbw which takes afair whack to wind over.

Also my manual reccomends 24volt but remeber the battery tech was pretty average when these engine where produced.
I think a decent 12volt battery will sufice.

Go to you nearest battery place.
Ask them if you can trial a battery for a day. Get the biggest sucker you can get within reason of course.
If it doesn't work no harm done, and if it does it will save you money and effort.

I checked into switches. JC whitney has one for around 180.00 for just that purpose.

series-parallel switch at just parts inc. for under $50.

I think the D2-6032N is the one you want, they will fax you circuit schematic

In my catalog - Mercedes - OM314, 4cyl, 3.8 liter (Shows yr models 1963 � 90)

Three starters available, only one is 24V
All available no problem

Price on the 12V models is appx $250 or $ 400 depending on which one you use.
The 24V model is over $500!
I have a catalog listing, if you can give me the oem starter # I can cross it to available parts and give you the 12V part #s
The oem number should be stamped on the starter housing.

*Again the series parallel switch system is a PITA you do not want to use this system unless there are no alternatives.
(using a 24v starter with a 12v battery will lead to premature failure - Low voltage is the enemy of starter motors - .)

note, I only buy this stuff (lots of it), I don't sell it!

The OEM# is a bit worn on the starter. The Delco Remy catalog number for a matching starter is #19024017. Though I hate to throw out a perfectly good starter. If the series parallel switch provides 24 volts to the starter then there shouldn't be an issue with low voltage. Correct?
Salty, there is a brand new 8d starting battery on board and it doesn't cut it. Maybe in the warmer weather this worked ok, but not now. BTW thanks for all of your help.

*I�ll check the Delco number at work tomorrow
To use a series parallel start/run circuit you will need a minimum of two 12V starting batteries and the associated wiring.
(There is more than that to consider but I have forgotten most of it- lol
Is the generator/alternator 24V? Or, is the engine is a 24v starter and a 12V charge system?) A �guest� switch may complicate things.

Good question CY. The boat has an 8d house battery. Two 12 volt deepcycle batteries which are set up IN PARALLEL. (I believe incorrectly) These are what the starter was connected too. And an 8d starting battery which, I believe wrongly set up, as another house battery. I did isolate that one and try it on the starter as I mentioned before, to no avail. I wasn't about to set up the "starter batteries" in a series as a 24 volt, without isolating them somehow. Also the whole thing is connected to a freedom 20 inverter charger with a link 2000 monitor. I think someones heart was in the right place, but I'm not real sure it is done correctly. I think the alternator is a 12 volt. Does that matter when charging a 24 volt battery? And yes there is a guest switch. One bank is the currently set up house batteries and the other is the two 12 volts/parrallel/starter batteries. I'm sure it works somewhat, probably just not the most efficient setup. Someone has been using it like this for some time.

Change the starter...this is giving me a headache!

IMO deep cycle batteries will not provide enough current for a starter application because they are designed for a different purpose. Honestly you need to choose to switch starters and get the right batteries, or rewire things correctly for the starter you have and get the right batteries.

one the bright side, you could use the deep cycles for your house bank when you rewire! starting batteries as house batteries are not ideal as they are not designed to be discharged much, if at all.

good luck
jerry

I have seen a manual override switching system that allowed (this is a little different) 36V start and 24V run (Alaska - cold) and it essentially used two heavy contactors, one at the 24V and another (mechanical) that was momentarily engaged to add another 12v after the initial starter circuit was engaged and the starter was turning (not yet at full speed). The additional power was added directly to the starter motor and bypassed the starter relay. In this system it was done to soften the blow of the starter drive into the flywheel but it may also work in your case. The charging/run circuit is the problem; it would have to be isolated while starting. But this could all be done with a bank of mechanical switches.
*Note this was a towboat and it had two auxiliary units (Detroit diesels) that ran all other circuits on the vessel. The engine start-run circuit was a stand-alone system and was only used once every two weeks when we shut down the main engines. We probably had a half-ton of batteries on board.

hi

I had this same problem last year. A 12 volt starter would not fit on the engine. Also the alternator was 24v. We hooked 2 12 volt batteries up at 24 volts and connected this to the starter. We also hooked a 12v/24v transformer to the batteries. All the 12v systems were then connected to the 12v side of the transformer. It has worked fine.

#19024017
I can't cross that number...

There might be two other possibilities beyond what's been discussed so far.
1) A starter/generator shop might be able to convert a 24V starter to 12V. A few years ago I had a 24V Leece-Neville starter for a US Navy Detroit Diesel 6-71 converted by a shop in Maine that is now closed. It worked fine. Was not terribly expensive, about $35, which was the same I paid to have him convert a 6V starter in an old bulldozer to 12V.
It may have been cheap because he had the parts lying around.

2) Add a second generator/alternator that puts out 24V, and use it just to charge the 24V starter batteries. This is available:
Mazda MX-3 V6 24V Alternatobr /> Product: Alternatobr /> Part #: F4000-51684
Brand: Bosch, Denso
List Price: $253.80
Prices As Low As: $122.46

Kia also uses 24V alternators in their Optima model.

I've installed Delco 24V alternators, but they're for trucks, and are quite heavy, heavy duty, large, and expensive for this use. But maybe from a truck junkyard...

The value of this approach is that it isolates your starting circuit from your house circuit, so that someone won't kill the starter by leaving a light on in a storage locker for a couple days.

Yes , yes and yes. I am aware of the fuction of house vs. starter batteries. Why they are wired this way, I have no idea. The existing alternater is crap, so I have the option of replacing it with whatever works. The house can be charged from an onboard generator. That is one way out.
I have thought, as Seo said, of seeing if the starter can be converted to 12 volt. Going to make a few calls tommorrow.
Colin, I would be interested in a few more details on that solution, if you would?
Jake, I saw a 12 volt starter in the Delco book, but it didn't look at all like the same body type. Yep, BIG headache. I'd really love to know how it was set up originally.

If I can't convert the starter, or find a 12 v, I will either get a 24v alternator and let that part of the system live by itself.
or....check into Colin's method (where can I get a transformer?)....or....check into the series/parallel switch. Once again thanks for the help at least I know that there are options. Gonna go scratch my head now..

OK, I have been in this game a long time and have never seen a 24v unit that was not available in 12V but hey � It�s a new world out there!
I am pretty darn curious about this and have learned a bit more. Bosch # 0001416010 is the starter number for your application (I think)
There are two Iskra starters available for 12V applications, #IS9083 or #IS9085 one is probably marine and totally sealed and the other is probably automotive (guessing). Iskra is a direct Bosch replacement. Tomorrow my distributor will call back with the complete story�
Your starter is a bit unusual looking in that it is a �sliding shaft� relay/drive. This is mounted on the end rather than on the side like a more conventional unit. (It doesn�t make sense that you have a 24v start and a 12V alternator, my suspicion is that A � alternator has been changed or B- it is a 24v unit charging 12V batts)

If you have the 8d for a house battery and have a small 12 volt engine starter battery, you are 90% there. My scanner is down or I'd send you a drawing. If you have the 8d's as house batteries leave them alone, and the Freedon charger and Link 2000 system is the same as I have sitting next to me at this moment. I solved my problem with a homebuilt inverter for 24 volts, but mine was for a different purpose (using and aircraft prop pitch motor to turn an antenna...)
If you have the starter battery you isolate the charger outputs, if your charger is like mine it will charge three batteries and has built in isolators. One set of charging circuitry will go to to the starter battery, the other two to your 8D house batteries. Then you lift the ground on the small starter battery and run it to a solenoid, to the plus side of the house batteries. You activate the solenoid with the starter switch, when you hit the starter, the solenoid closes bringing the voltage at 24 volts (series batteries) to the starter, all other items run from the house battery, when the key switch is released the ground lifts isolating the starter from the house system and allows the charger to function normally. If you will write up exactly what you have, and include a crude drawing and send it to me, I'll draw a system for you using pretty much what you have on hand. Check out the price of a 12 volt solenoid, it doesn't take much more than that, and I can find a small 12 volt relay at digikey. E-mail through the forum if you wanna do this.

I use "New England Alternator and Starter Motor, Co" 401 823 1001, I have a diesel Toyota Landcruiser with a 24v starter, and 2 x12 v batteries in series , and all of the above is true, as well as the fact that it is sometimes possible to re build a 12v into a 24v. and vice versa in some cases,call John Socca,proprietor, his service and timing are impeccable.Not to mention he has re built SVPelagic's starter and alternators at one time or another.Stephen

hi

I had a 6 cylinder Volvo go tits up in one of our mussel boats this summer. We had a 4 cylinder Cummins is the building and decided to swap them. We realized later that the Cummins was set up for 24 volts. The transformer was an off the shelf item from our local engine re-builder, sales dealership and cost about 100$. Very simple to install. 24v leads marked on 2 posts, 12v on the other 2. It is about the size of a 1 litre tetra-pak and just bolts on to a vertical surface.

Snyder Mucall

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