Cab Upgrade - Standardize around 24v?

[gslader]

I am about to embark on a series of cab upgrades on my M1078a1 (interior lights, exterior lights, cab audio, etc) and my plan is to add a secondary fuse block and run it all off of 24v. I’ve read through the multiple battery and alternator threads (which contain great information) but don’t address this head on.

My rationale for doing this is the that my I^2R losses will be lower, exponentially (for example a 50watt load would have 12% of the I^2R losses at 24v versus at 12v for a given resistance), than using a 12v system. Additionally, this should be a better match for the Niehoff alternator which favors 24v loads.

For reference I will be installing 4x 6TL batteries (I know it’s overkill) and am running the stock Niehoff dual voltage alternator. I keep it on a 24v tender when not in use and have an Eaton equalizer on order along with a smart isolation switch.

I am heading int he right direction or is there a fundamental flaw I’ve missed?

 

[Guruman]

My only thought would be that the selection of devices (lights, audio, etc...) would be far greater and less expensive in 12 volt.

And... Although what you said is true, 12 volt systems have been around long time, I'd think your equalizer would overcome any 12 v weaknesses with the alternator.

Realistically, how many amps will you be running? I guess if you are going to use a LOT of power, then the 24v route might be worth the extra expense. Personally, I'd think if the load was going to be a reasonable part of he equalizer capacity, (say 80%??) I might jsut let it handle the additional 12v loads.

Good luck, let us know how it works out.

 

[Ronmar]

Batteries are ultimately loads. any power you take out must be put back on top of powering operational loads. Are you planning on running for very long periods of time with the engine off? If not, then a large battery bank makes no sense. If you are, then the stock 100A alternator 12/24 configuration to recharge a deeply discharged 240AH battery on a regular basis plus power operational loads makes no sense.

Are you planning on cold soaking in Siberia for a week before startup? Again, it would be rare that you will ever need that much reserve capacity, and if you were operating under those conditions, there are other things that make way more sense than a grossly oversized battery, like an arctic heater warming engine and battery bank to boost reserve capacity and ease startup… And you are still left with the 240AH plus load vs 100A alt issue…

For a given cable cross section, your losses will be lower for a given wattage of load at 24V than at 12V. But with large gauge cables that are not very long, not such a large issue. How much load are you planning on running? And again, if you have pulled a large ammount of energy out of a large battery, once running that large battery needing charged is going to limit your available power untill it is full…

As mentioned, your selection of native 24V accessories is not as great as those designed for 12V…

To address your specific issue, I would probably stay with 12V accessories for simplicity and selection. I would then use a power converter in the cab to draw my accessory power from 24V. Victron makes some nice ones, I was looking at the 70A version that has remote control/cutoff capability So you could control this accessory buss with a dash switch. They can also work in parallel to double the capacity if you need more than 70A… About $140…

The further extension of this is to power ALL the truck 12V this way. Keep the alternator output connected to battery 12 and 24(required to get full alt output) and allow it to simply operate as a battery balancer… Then disconnect the 12V at the cab with a battery disconnect switch(save for emergency power in case of converter failure). Then have the converter power the 12V in the power panel. The stock 24/12 alt configuration is only capable of about 2000W. In 24V only mode it should be capable of greater output (closer to 2800W), so this in effect would lower the load on the alternator making it’s life a little easier. A 1078 with incandescent lights pulls about 26A for lighting load, so a 70A victron would be under 50% load operating the truck… LED lighting would lower this load significantly…

Running like this would almost make the four battery 6TL wet cell 240AH bank a viable option. The 240AH is looking for 60A for bulk charge(25% of AH rating) and the remaining 40A would feed the 70A@12V Victron OK, so you would be around 100% load worst case. 240AH of AGM’s would still be out of the question needing 45% of the AH capacity From the alternator(108A) all by themselves…

And as always, I don’t recommend anything larger than 100-120AH(single pair) in the stock 100A 12/24v alternator configuration…

 

[coachgeo]

delete me..... Ron states it better than I

 

[gslader]

Batteries are ultimately loads. any power you take out must be put back on top of powering operational loads. Are you planning on running for very long periods of time with the engine off? If not, then a large battery bank makes no sense. If you are, then the stock 100A alternator 12/24 configuration to recharge a deeply discharged 240AH battery on a regular basis plus power operational loads makes no sense.

Are you planning on cold soaking in Siberia for a week before startup? Again, it would be rare that you will ever need that much reserve capacity, and if you were operating under those conditions, there are other things that make way more sense than a grossly oversized battery, like an arctic heater warming engine and battery bank to boost reserve capacity and ease startup… And you are still left with the 240AH plus load vs 100A alt issue…

For a given cable cross section, your losses will be lower for a given wattage of load at 24V than at 12V. But with large gauge cables that are not very long, not such a large issue. How much load are you planning on running? And again, if you have pulled a large ammount of energy out of a large battery, once running that large battery needing charged is going to limit your available power untill it is full…

As mentioned, your selection of native 24V accessories is not as great as those designed for 12V…

To address your specific issue, I would probably stay with 12V accessories for simplicity and selection. I would then use a power converter in the cab to draw my accessory power from 24V. Victron makes some nice ones, I was looking at the 70A version that has remote control/cutoff capability So you could control this accessory buss with a dash switch. They can also work in parallel to double the capacity if you need more than 70A… About $140…

The further extension of this is to power ALL the truck 12V this way. Keep the alternator output connected to battery 12 and 24(required to get full alt output) and allow it to simply operate as a battery balancer… Then disconnect the 12V at the cab with a battery disconnect switch(save for emergency power in case of converter failure). Then have the converter power the 12V in the power panel. The stock 24/12 alt configuration is only capable of about 2000W. In 24V only mode it should be capable of greater output (closer to 2800W), so this in effect would lower the load on the alternator making it’s life a little easier. A 1078 with incandescent lights pulls about 26A for lighting load, so a 70A victron would be under 50% load operating the truck… LED lighting would lower this load significantly…

Running like this would almost make the four battery 6TL wet cell 240AH bank a viable option. The 240AH is looking for 60A for bulk charge(25% of AH rating) and the remaining 40A would feed the 70A@12V Victron OK, so you would be around 100% load worst case. 240AH of AGM’s would still be out of the question needing 45% of the AH capacity From the alternator(108A) all by themselves…

And as always, I don’t recommend anything larger than 100-120AH(single pair) in the stock 100A 12/24v alternator configuration…

Dang. Ronmar for the win again! There is a lot there for my small mind to digest. I am most intrigued by your paragraph about powering all of the truck’s 12v with a converter.

The fundamental issue that I have with OEM set-up (besides mismatched alt to battery sizing) is that by tapping 12v out of the middle of two batteries wired in series for 24V there will always be a charge/discharge imbalance. Is there a way, with the stock alternator, to just drive two sets of batteries in series (essentially 2 banks of 24v) then use say a 100a 12v buck converter to drive any 12v loads?

My understanding is that this doesn’t work because the alt needs to “see” a 12v load. Could you create a “parasitic” (when the engine is on) 12v load (maybe just a resistor) so the alternator sees a 12v load but the alternator is just charging the two banks of 24v - keeping the series wired batteries balanced (versus having one of the two batteries tapped to drive 12v loads). If easer to discuss live happy to chat on the phone.

Thanks again for the very thoughtful response.

Gavin

 

[gslader]

delete me..... Ron states it better than I

Every piece of incremental information is helpful!

 

[Ronmar]

The only problem with the 12/24 alt setup is when you draw 12V out of the middle of it. The alt regulator acts as a balancer working to deliver 1/2 of the 24V output to the 12V output. IE: 14.2/28.4 I tried running my alt without the 12V years ago and it did not appear to work(alt would not come online). which told me the regulator is looking for that 12/24 relationship. I revisited this a few weeks ago playing with a load tester and actually got the alt to come online with the 12V disconnected, so maybe I had some other issue back then. At any rate it was still not right as the 24V would not come up to it’s normal 28.4ish, halting at around 27. I tried applying a small load to the 12V output with no change, so it is wanting some sort of feedback from the battery relationship. Maybe it was going into a trickle mode to try and charge a bad battery bank until it starts seeing what it is wanting to see…

At any rate, it is not really important to disconnect the alt 12 output to the batteries, if you disconnect the 12V truck load, The dual volt alt output will continue to maintain battery balance as it was designed to do. It should work just fine that way…

As for using a converter to provide the 12V truck loads, not a new thing, It is what I plan on doing if my dual volt fails, as I can replace it with a 24v truck alt and equalizer/converter for a fraction of the cost of a replacement dual volt… There are Bussman converters, Vanner makes some also that I believe were used in HEMT’s. They can either be installed as an equalizer, or to just connect to the 24 and output 12 to the vehicle loads Without connecting to the batteries. The equalizers have a non adjustable output, they divide by half whatever is sensed across the 24V input. The Victron converters look like they will also work, as they have a very low input voltage cutoff like the equalizers, which is important to maintain the 12V output while the 24V sags during start. This is easy to get around though as you can back up the 12V control voltage from the battery while you are cranking the starter to insure uninterrupted starts. Victron also has an adjustable output, so you can set it at whatever voltage you want to run the 12V truck/accessories at…

 

[coachgeo]

..... The Victron converters look like they will also work, as they have a very low input voltage cutoff like the equalizers, which is important to maintain the 12V output while the 24V sags during start. This is easy to get around though as you can back up the 12V control voltage from the battery while you are cranking the starter to insure uninterrupted starts. Victron also has an adjustable output, so you can set it at whatever voltage you want to run the 12V truck/accessories at…

no matter the alternator ..... if wired like the FMTV to where the alternator is not even "excited"/activated until after the engine is running..... why is this a projected issue?

 

[Ronmar]

The control power/24v ign relay, is powered by 12V from CB 70 via the ign sw. If the converter is providing all the truck 12v, and drops out while cranking, so will that relay, removing trans power and start circuit power, which will interrupt the crank…

 

[olly hondro]

A small 12v battery from a motorcycle or lawn mower application connected to the 12v side of the DC-DC converter would buffer a converter outtage for a little while. I only mention that as I have done it with a Todd Engineering 160 VDC to 14 VDC converter successfully. The application was an electric truck conversion with a 144 VDC battery pack to run the stock 12 V chassis electrical stuff (lights, turn signals, etc). That system worked flawlessly until I ran it thru a carwash with the underhood mounted converter powered on....so, yes, in the cab is better.

 

[Ronmar]

A small 12v battery from a motorcycle or lawn mower application connected to the 12v side of the DC-DC converter would buffer a converter outtage for a little while. I only mention that as I have done it with a Todd Engineering 160 VDC to 14 VDC converter successfully. The application was an electric truck conversion with a 144 VDC battery pack to run the stock 12 V chassis electrical stuff (lights, turn signals, etc). That system worked flawlessly until I ran it thru a carwash with the underhood mounted converter powered on....so, yes, in the cab is better.

Yep, that would do it, as would a temporary tap to the middle of your 24V bank. Even if you had a straight 24V alternator, you could still draw 12v from the middle of your 24V bank for a short while, to get you where you need to be in the event of a 24-12 converter failure.

They actually make a commercial device called start guard to cover critical electronics during a start cycle. I pulled one out of a dumpster along with a 20A 24-12 converter but havn’t played with it. I suspect it is a capacitor bank with a resistive buffer circuit(not particularly heavy) The one I have says it can supply 8A@13.8V for 20 seconds…

 

[olly hondro]

Yep, that would do it, as would a temporary tap to the middle of your 24V bank. Even if you had a straight 24V alternator, you could still draw 12v from the middle of your 24V bank for a short while, to get you where you need to be in the event of a 24-12 converter failure.

They actually make a commercial device called start guard to cover critical electronics during a start cycle. I pulled one out of a dumpster along with a 20A 24-12 converter but havn’t played with it. I suspect it is a capacitor bank with a resistive buffer circuit(not particularly heavy) The one I have says it can supply 8A@13.8V for 20 seconds…

Yes, such a system would be paired with a straight 24V alternator. We have discussed that somewhere before; I like the idea of using a common alternator from CAT construction equipment. I am anxious to road test with that configuration to flush out any unintended consequences.

 

[Ronmar]

Yep. I have a Vanner 100A balancer/converter that I am going to install and disconnect the 12V truck load out of the middle of the bank. I will leave the alt 12/24 connected to the batteries, but only draw power from the 24V batt/alt output… The next step would of course be to shift to a straight 24V alt, but this first step will do all the wiring modifications necessary for the full conversion…