Just 24 volt

[freecr]

Hello all,

Its summer time so back to it…

I’m interested in switching to only having a 24 volt system. I know others have done this or have planned on doing this while others bought their trucks already this way so I know it’s doable. For the radio, trailer controller and a couple of 12v outlets I’ll use a 24/12 converter. I know I’ll need to convert the lighting to 24 volt but I was already planning on installing all LEDs anyway so no extra work there. I don’t know whether the gauges use 12 or 24v. Does anybody here know? I deleted the CTIS so no 12v needed there. I don’t think there’s any other 12v stuff on the truck but if there is please tell me. I have a M1079 and will have a 24 volt solar system for the shelter. Being able to charge everything via the engine if needed is appealing but way simpler on mono (24) voltage. I haven’t decided yet on one massive battery bank or two independent but selectable/combinable battery banks. Obvious advantages/disadvantages to each and why I haven’t decided yet. So anyway, back to the 24 volt question(s)…

If I don’t use (don’t connect) the 14v leg from the alternator, are the entire 100+ amps then at 28 volts? From what little information I’ve read it seems like the 14 volt leg is only as needed, ie demand based. Does this sound right? I hope so as this is just convenient and the cheapest route.

Or

Can I use a 28 volt (only) regulator instead of the 14/28 volt one currently attached to my alternator? These are common on eBay, as long as I find one that is rated high enough, of course. Do they all share common connections? I’m guessing that they do and the alternator puts out whatever it puts out and the regulator converts it to the correct voltage (if needed/demand based). Am I correct?

Hopefully I don’t need to buy an alternator.

Thanks for any help.

With any luck there will be a consensus.

 

[coachgeo]

...I’m interested in switching to only having a 24 volt system. I know others have done this or have planned on doing this .....

hmmmm....... don't recall anyone doing this,. but maybe I got early onset Oldtimerz disease?? If the system is working..... why would you want to change anyway?? now if you have to redo things cause it's not working... then that certainly is one possible way to solve things.


Do recall folk have completely separated the two going with something like a new alternator from Double Alt (double-alt.com) and changing the battery wiring to one bank of two batts wired in series for 24v... and another bank of two tied in parallel for 12v and they two not wired together at all. The double-alt being a 24v alt stacked back to back with a 12v... charges each bank accordingly. All 12v items (headlights etc) fed from the 12v bank and all 24v fed from the 24v bank.

 

[freecr]

People have done it for various reasons. I didn't want to ask each of the people that mentioned doing/have done individually so I asked the group. I want to do it to simplify things especially for camper battery bank and If I the first two ways are incorrect and I need to buy a different alternator I may as well upgrade to bigger alternator anyway so I want to know ahead of time so I don't end up regretting later.

 

[tennmogger]

Theoretically you could install a Vanner Battery Equalizer across the batteries and then use only a 24 volt alternator connection. The truck wiring would not have to change.

Check out the Vanner site if you are not familiar with battery equalizers. http://www.vanner.com/battery-equalizers/

 

[coachgeo]

People have done it for various reasons. I didn't want to ask each of the people that mentioned doing/have done individually so I asked the group. I want to do it to simplify things especially for camper battery bank and If I the first two ways are incorrect and I need to buy a different alternator I may as well upgrade to bigger alternator anyway so I want to know ahead of time so I don't end up regretting later.

Seem to recall the discussions on this now. thanks to you and TennMogger for jarring my memory.

IMHO since the existing alternator charges ONLY at 24v.. with wiring and items as they are switching to a different 24v alt with higher output really causes you no disadvantage.... seems more of an advantage to keep like it is compared to replace/rewire/convert the 12v to 24v. Keeping it as is means NO converters needed for truck or camper. Existing 12v will not need to be rewired... items that in camper... more often are 12v anyway (lighting, LP heater fans, water pumps etc.) will not need converter installed etc etc. if you wire camper the same Series / Parallel 24v/12v

With the Series / Parallel wiring (allowing to charge at 24v.. yet run 24v and 12v items) from large banks while not perfect...... is not so imperfect to not be practical by any means seems to be what has been pointed out.

The fellow whose advice am following (30yrs in solar industry) suggested to stick with everything like it is for reasons above with these trucks setups and wire the solar battery bank to work in same way.... 24v series / parallel accepting charge from both solar (1000w wired for 24v charging) as well as the existing 24v alt. (after truck battery bank charged.)

But.... that being said...... with the merits of changing to ONLY 24v or not; I think already discussed in those other threads*, .... will refrain discussing that subject from this point forward so not to re-hash that topic in your thread. My apologies.

Back too... "how to switch to only 24v" .


*https://www.steelsoldiers.com/showthread.php?176504-Fmtv-no-more-dual-voltage

 

[freecr]

Tennmogger,
I will most likely have two battery banks, one with just 2 batteries and the other with 8, so I will just run the laughable 12v draw through a cheap buck converter. The radio (and possibly the gauges) wont pull enough amperage to justify a Vanner and the big bank will probably have some sort of battery equalization through the solar charge controller. All lights are changing to aftermarket LEDs anyway. If I were to maintain the 12v side I could use the stock headlights but all the rest are going anyway. Those 24 volt LED headlights are spendy, so that sucks. So, do you think I can get away with just using the 28 volt leg? Dumb question, I know I can just use the 28 volt leg. Do I get the 100+ amps with just one leg or do I just get the 60'ish amps?

 

[Awesomeness]

I know others have done this ... so I know it’s doable.

Are you just starting your post with such lofty claims because you don't want it to turn into a thread explaining why you shouldn't do it? I don't think there are any credible stories of anyone having done this yet. We get posts on here periodically, typically from a new member that doesn't even own one yet dreaming big, but I haven't seen a real case of it.

Personally, I'm very skeptical of ideas like this. I'm an engineer, and get a snicker whenever I see posts [on all kinds of forums] where users lament the "poor designs" engineers come up with, how some aftermarket "upgrade" is such an improvement, etc. Sure, engineers make mistakes sometimes, but it's actually most often that the onlookers just have very little understanding of the specifications or intent that the engineers were designing to meet. So the real question you need to answer is "Why is the FMTV dual voltage?". Engineers didn't just sit around and go "Hey, know what would be neat, Joe? Lets make everything really complicated by having two different voltage buses running through the truck! Good idea, John!" They probably did it quite reluctantly, after there were no other options to fulfill the requirements. Sometimes it's that the military requirements actually asked for it (e.g. "must have 12V and 24V connections"), or that they include some other very difficult requirement(s) that required it (e.g. "must be able to operate to 125°F" and the only transmission controller available that can go that high is 12V, so you have to add it).

I'm not saying it can't be done. With enough will, time, and resources, you could rewire the truck to any voltage you wanted. But it would be good to understand upfront why it was so important that they made the truck dual voltage, and what capabilities you're losing (or have to replace with a 24V equivalent) by switching.

You might start by tracing out the 12V wiring in the TM's wiring diagrams, and make a list of everything that is connected to 12V.

 

[mechanicjim]

"Do I get the 100+ amps with just one leg or do I just get the 60'ish amps?"

On the Niehoff's the base alternator is made 28v then with SCRs power is taken to feed the 14v side. so technically with 14v load the 28v output is lower than if there was no load on 14v. but this also means that with no load on the 14v side the alternator/regulator will just give all its power the 28v side. so yes technically if you take the 14v side off then the alternator basically becomes a 28v unit. side note these always need the 28v to work you cant just make them a 14v unit as the field coil/regulator operate on the 28v side.

 

[coachgeo]

"Do I get the 100+ amps with just one leg or do I just get the 60'ish amps?"

On the Niehoff's the base alternator is made 28v then with SCRs power is taken to feed the 14v side....

SCR = Thyristor

https://www.youtube.com/watch?v=GydYhUdDeTI

 

[coachgeo]

Do I understand right that overall the 14v output is so low (except when lights are on) that in effect the alternator is putting 90%+ of all its amp output on the 24v leg. In the Niehoff Alternator application on these trucks there is no 14v leg used for battery charging... The OEM bank of batteries are charged at 24v ONLY?

Question..... with that in mind..... Does all the 12v draw items NOT draw a power from the batteries when engine is running but instead draw straight from 14v alternator output? How/what manages where 12-14v items draw power from between battery or alternator??

Massive thanks. Love learning new things.

 

[mechanicjim]

hey Coachgeo no actually,
the way it works or how it should work is loads are drawn from batteries and the Alt works to replenish this. think of it as Loads are the engine(they use fuel), batteries the fuel tank(they supply the fuel, and the alternator is the gas station(where you spend an arm and a leg to refill the tank).

In these dual output setups yes most of the power is being supplied to the 28v side of things while the 14v side is there is feed the 14v loads and charge up the batteries. technically the 14v side should be tapped off the 28v batteries at the lower battery post( so you get 12v). the 14v terminal of the alt is also connected there in a way that allows it to refill this battery to keep from unequal discharge of the lower battery. if you have the LBCD that is the point the battery and Alt are connected before the loads.


you can always test the draw with an DC or AC/DC ammeter(clamp style) on either side to the 14v or 28v post of your alternator to see how much is being used by either side for reference.

 

[coachgeo]

..... if you have the LBCD that is the point the battery and Alt are connected before the loads.....

LBCD - Load Balance Control Device. (that thing under the spare tire that also acts as a reverse polarity protection)

 

[coachgeo]

.... In these dual output setups yes most of the power is being supplied to the 28v side of things while the 14v side is there is feed the 14v loads and charge up the batteries. technically the 14v side should be tapped off the 28v batteries at the lower battery post( so you get 12v). the 14v terminal of the alt is also connected there in a way that allows it to refill this battery to keep from unequal discharge of the lower battery. .......

so the alternator does some charging at 14v (as described above) for this one bank that has the 12v draw... and also charges the whole bank at 28v?

 

[mechanicjim]

so the alternator does some charging at 14v (as described above) for this one bank that has the 12v draw... and also charges the whole bank at 28v?

yes it does, so instead on needing a separate battery equalizer( like the Vanner products) the Alternator does it all. if you had a single voltage output alternator and wanted to tap off for 14v loads you would need to "equalize the system" or run a separate battery for the 14v loads.
this is why the military choose the system the way they did,
option 1 make the truck a single voltage( this limits the off the shelf parts they could use(lights, CITS, transmission, etc),
option 2 single voltage Alternator with a battery equalizer allows use of cheaper off the shelf parts but is limited by the size of equalizer available at time of design( they have gotten better smaller with higher output),
option 3 dual voltage output alternator allows use of cheaper off the shelf parts and can be design with multiple output options ( 100 amp,200 amp, etc)

 

[freecr]

Just to be clearer about why I would consider this:

I’m a huge fan of “if it ain’t broke, don’t fix it”. I just happen to be in the weird position of considering whether I need or can justify a 200 amp alternator. I have already purchased the components for a solar system and like the idea of being able to charge the van’s battery bank with the trucks alternator if and when needed. Obviously I could use this bank to jump the truck or even as its batteries for driving if for whatever reason just so long as it has the same voltage. So I’ll configure the Van’s battery bank to 24 volts (not, 12, 36, or 4. So at 24 volts it could jump the truck and be charged when/if needed. Back to this in a minute…

My question was to use 24 volt only charging system and a 24 volt to 12 volt converter. I was never considering converting all of the 12 volt systems on the truck to 24 volts, just the lights. Everything else that is 12 volts was for sure going to stay at 12 volts. I believe, but of course don’t know for sure, that other than the lights the remaining 12 volt items are very low draw items. So if the lighting is 24 volts would the remaining 12 volt system items be of such a low draw that a simple buck converter be sufficient?

I rotated the box around which I’m sure will be a whole “why did you do that” side topic that’ll detract from this topic and while I usually like that It doesn’t take much to hijack threads or get off topic I kinda want to know about this. Because I rotated the box around I need to fabricate a new bumper, hitch and tail lights and I also need to change the marker lights. So, I’m already committed to moving tail lights and marker lights and have absolutely decided to go with civilian style LEDs for all of these.

So I’m already changing the lights and I’m seriously considering upgrading the alternator. So back to the using the van’s battery bank as a backup for the truck…. If the truck only needs a very small amount of 12 volt supply to operate and I install a converter in the kick panel for that then I can also use the 24 volt backup to run the truck. Or I also would have to hook up the van’s bank in the dual 12/24 matter. It’s a silly question I know but if I’m in the market for an alternator and already replacing lights this is the time to consider it. The 24 volt only alternators seem easy to find and tend to be cheaper. I can just as easy buy 24 volt LEDs lights as 12 volt ones. I can also hook up the van’s bank 12/24 it just more cable.

So if the 100A alternator does indeed output near its 100A capacity at 28 when there is no (or little) demand on its 14v leg, then that may be enough and I shouldn’t need to upgrade the alternator. I was batting this around at 60ish amps, at 100 amps it’s a little less enticing.

 

[coachgeo]

Someone please put an amp meter on the 28v and 14v output and see what you get. It has been reported.. but not clarified... that these alternators are "adverse condition" 100 amp rated.... and may well put little to significantly more amps out when NOT in adverse conditions. Am curious to what might be found. My trucks not close by.

 

[Awesomeness]

Isn't it also common to split to using two separate alternators (one for 12V, one for 24V)?

 

[coachgeo]

Isn't it also common to split to using two separate alternators (one for 12V, one for 24V)?

can do two seperate with new brackets.... or as mentioned earlier with "double-Alt" which is a 12v and 24v alt. stacked back to back and sharing a single shaft.