Geoff Weeks

I'll agree with that statement. But the one single thing that draws the most and determines the limits is cranking and to a lesser extent firing of the injectors while cranking. Look at it this way, if cranking a large bore diesel in cold draws the system voltage down to ~6 volts, that has cut the system in 1/2. a 24 volt system that looses 6 volts while cranking is still at 18 volts. It is all about getting the truck running, once that is done, the alternator carries the load. You can afford to loose 6 volts with a 24 volt system, you can not with a 12. Injector firing is done at a much higher voltage on the new trucks, then system voltage. If the system is pulled too low it can't even fire the injector even if the engine is cranking fast enough to start. It is becoming more and more common on newer vehicles to have charging voltage controlled by the ECM in order to quickly replace what was drawn off when the vehicle was shut down. Storage batteries (common lead acid types) can provide small amounts of current for a long time but are extremely limited in how large a current draw they can provide for even a short time. It isn't a liner graph. A Maxwell supercapacitor can provide enough current to start a big bore diesel in -25F in the form factor of one Gp 31 battery, but can be totally depleted in 25-35 min by connecting a single headlight across it. It is the opposite of a battery, the Maxwell can supply huge amounts of current for a short period. It does not store more energy than even a single group 31, but can release it all at once. This is proven by the fact a single gp 31 can recharge the Maxwell multiple times (charging current for the Maxwell is less than 18 amps) Key off loads could be handled by 4 lead acid batteries in parallel and carry that load for a week or more, but not be able to crank the engine in the cold because the current draw exceeds the ability of the battery to provide, either provide more, or reduce the current needed. doubling the voltage cuts the current in 1/2. doubling the voltage does not increase the total capacity in watt/hrs of the system. You are still storing the same amount of energy, but can better access the stored energy when a brief large draw is on the system. I don't claim to be schooled on the latest, but the laws of chemistry and physics don't change. I do have an fair but by no means complete understanding of the modern systems on vehicles. I am by no means an expert. By raising the voltage, you are reducing the current required, and current is the limiting factor. Once the truck is running the charging system supplies not only the current to keep it running but also the current to replace what was used to start.

I think you are confusing analog DC , where the only choice is "what is the voltage" and digital where a unique identifying pulsed square wave is placed on the buss. The individual modules respond to only their "query" on the buss. Like an old fashion party line telephone. These systems run on much lower voltage then the rest of the "normal" vehicle electrical system. It is the same way someone can be streaming a movie on their computer while someone else in the same house can be listening to music stream, while a third is downloading a program, all on a single modem. the signals get sorted not by voltage but by digital identifier.

If I had to guess, I think it is far more to do with key off draw, which is becoming critical in all vehicle as the electronics become more and more complex. In most cars, for example 50ma was the max figure, I have heard that has be increased on the newest stuff. How that translates to trucks, if key off loads go up, the truck is trying to start with less than full battery. We have reached the limit of what 4 gp 31's can crank in parallel. It becomes cheaper and more reliable (in theory) if you raise the voltage, decreasing the current needed to crank. The choice would be more gp 31's in parallel, adding to weight and storage room or take those 4 gp 31's and divide into two groups of 2 in series. The same amount of power is used, but the highest load (cranking) is a bit more tolerant if the voltage is higher and the current less. It is just like 6 volt can crank a 450 CID engine if all the connections are perfect, but 12 volt will still crank if the connections are a little less than perfect. It get worse in the cold. 12 volt batteries in parallel can do fine in normal temps but can struggle to produce the same current when cold. While job is the same, the ability to make the required current at the lower voltage exceeds what the battery can do when cold.

This made me think that

I think it has come down to how well things have been thought out. One big disaster is: backward compatibility. It is like "feedback carburetion" was. Bandaid on top of badaid until the system collapsed. Once Mfg finely came to the conclusion they couldn't meet requirements with what they always had turned to, then and only then did things get better. Once carburetors were abandoned, and FI took over we went from engines lasting 100k to 2x-3x. Engine life wasn't the thing that pushed the change, it was emissions. 24 volt has always been better in higher power use applications. It was why it was used elsewhere for more that 1/2 a century. 32 volt has been used in marine for a long time, 36 less so. 48 has an operating voltage of over 50VDC and is getting well into the area that you solve one issue and create 2 more. 24 volt is far better than 12 for cranking big bore diesels. What kept it out of this part of the world was backward compatibility. A 12 volt trailer would need retrofitting to be towed by a vehicle supplying 24 volt to the trailer. Back in simpler times a nose box and resistors allowed a 12 volt tractor to tow a 6 volt trailer. When designing electronics, it cost a little more (not much) to make the compatible with multiple voltages around the same range, so stuff like ABS, radios Stab control, engine controls etc, could be made future/backward compatible but have not. The last time we went though a voltage switch vehicles were far simpler. Still VW kept 6 volt until the mid 60's, and 6 volt bulbs (including sealed beam headlights) are still readily available more that 50 years after the last car using them were produced.

You misunderstand me, I wasn't saying it had anything to due with lighting. I only mentioned the lighting in terms of it being the only thing on the buses that WASN'T 24 volt. Voltage has nothing to do with the problems Volvo has created. Some have pushed for higher voltages (Elon!). The higher the voltage the thinner the wire can be for the same "work". It brings other problems like flash over and the need for wider air gap in relays and switches for example. Problems multiply once the actual voltage exceeds 50 VDC, so there is a practical limit on the higher end also. Most problems seam to exist when more than one voltage "system" is used on one vehicle. It come more from implementation (corner cutting) then from the fact there are two (or more)voltages used. Volvo seams to have chosen the route of 24/12 voltage on their trucks to meet an end result, not as the end result. It was their "solution" to implementing some requirement, not the requirement has to be 24 volt.

Back when I was bringing "gray market" European buses to meet DOT spec's the only thing that required 12 volt were Sealed Beam headlights. Sealed beam's were required at that time and no 24 volt sealed beams met the DOT required beam pattern. At that time Motorcoaches (MCI, and others) were also 24 volt, andused either a Vanner battery balancer or some solid state DC-DC were just coming on the market. As others have said in many parts of the world 24 volt in commercial vehicles is the norm. The only today keeping it from being is backward comparability with older trailers and equipment. 12 volt cab accessories could easily be handled by a 24-12 DC to DC converter.

Voltage doesn't effect mutiplexing as far as my understanding. That is done with a digital signal, which is why modules have to be "programed" to the vehicle and can not be interchanged at random between similar vehicles. Either way it is the mfg choice of engineering that had led to the problem, not the voltage nor the EPA (24 volt is not mandated). It is never "we have to make a crappy vehicle" it is "we choose to, because it is cheaper and more profitable".

Most motorcoach's here run 24 volt. It isn't about the voltage or the EPA, it is about the mfg implementation of an ill thought out solution to a power issue. This is all on Volvo.

They used to, IDK anymore.

Pretty much, nothing on the front axle and one S cam on the rear all the way out, and the other???

Ok, I am going to bow out. You seam to be set in your plan, I have expressed my concerns, and what is legal, good luck.

well, I don't see any brake chambers on the front axle. That is not legal either. Time to fully assess what you have and don't. Law is brakes on all axles, functioning and plumbed with DOT approved fittings. Where you are now is no where near legal, and "upgrading" has to take a back seat to getting legal.

Engine is obviously a replacement/reman, but that does help with axle ratio, unless those also have been replaced.

Likely a Big Cam 3, Could possibly be a Small Cam Magnum, I can't see enough of the cam follower covers to know. Would be nice to know axle and ratio. Talk about rode hard and put up wet. A little cleaning would make it sell better.