12v- 24v question

[Hammer]

Ah, and tell me again why we can't also run the batteries in parallel for a high amp 12v load?
I know a number of OTR trucks have multiple batteries (2 or 4), that they run most stuff on 12v(in parallel), and run the starter and a couple other things on 24v.

Is the only reason NOT to do this is because of load balancing the batteries?

 

[gimpyrobb]

I think if you wanted to run 2 12v batterys off a power converter, a dual battery isolator would be a good idea. From what I understand, even very close tolerance batterys will have different internal resistance and one will deplete the other. Over time, killing one or both batterys. I sure would like Bjorn to check out this thread.

 

[Hammer]

Ok, but my dodge, and a LOT of other trucks I know of, run 12v batteries in parallel.
I know that replacing those batteries should ALWAYS be done in matching pairs (from the same batch is even better).
On the cement trucks I worked on, we had 4 batteries, we had full 12v for everything in the truck except the starter and glow plugs. It would run all four batteries (each pair was parellel for two 12v banks, then the starter and glow plugs would pull off both banks in series).
One note, the alternator was 12v for the system.
Not sure if that would be the only thing I would have to change to properly run the 12v in parallel for extra power items, but in series for the original military items.
I would prefer to leave the system all 24v. But I would like to have 12v that isn't limited to a fairly small load.

 

[Hammer]

Oh yeah, I was planning on putting a solargizer on each battery, which would help keep them topped off fairly well.

 

[gimpyrobb]

I am out of answers. Someone smarter than I will have to take over. I have posted all that I am sure of. Everytihng else I don't have a great grasp on, and I don't want to spread incorrect info.

 

[Hammer]

Yeah, having CORRECT information is the goal here. Thanks for all you have provided so far though. Hopefully we can get this cleared up.

I know it can be done, I only wonder what we would have to change to make it happen?
If I only need to get a 12v alternator, and swap a little wiring around, then I am all over that.

I still want a converter for my wife's truck though. That one will be 'stock'. Any mods will be along military lines of what they have/would change.

 

[powerhouseduece]

So would it be ok if I ran just a pyrometer and maby a small cb off one battery?

 

[Hammer]

Most pyrometers are self powered (the heat in the probe generates the small voltage used by the gauge.) With the light in the gauge being the powered part of it (easy swap to 24v bulb.)

 

[Hammer]

http://bus.getdave.com/Docs/12Von24V/
Has some good info on 24v systems needing to run 12v.
It doesn't show the system like the ones I have seen though (probably because of the 24v charging system).

The stated reason for not running both 12v and 24v at the same time is listed as:
"This is generally a bad idea because it means your draw on your batteries is out of balance (unless you match the two 12V circuits) One battery will continuously lose more charge than the other and then be at a lower voltage. The charger on your bus does not charge the two batteries separately, it simply places 28V or so across the battery terminals. This means that eventually one of your batteries will die, or the other will be overcharged or both. "

But if both batteries match, and I have the means to individually top off each battery with solargizers, wouldn't that be the easy answer?

The other downside of this way is that you have to wire in separate grounds to use it this way. You cannot use the vehicle as a ground because that is the 'other' system.

 

[powerhouseduece]

Hammer, for some reason the pyro I bought is from autometer, K type thermalcouple, and it has a 12v feed and a nother feed for the lights. at this point I might just get a inverter

 

[Hammer]

An inverter would be a much safer and more practical way to go for light loads like this.

 

[powerhouseduece]

Ok thank you sir.

P.S. I did not mean to "jack" the thread

 

[Flea]

You "should" be able to run the batteries in series and parallel. However, for the 12 volt (parallel) side of it, you would need dedicated ground wires - i.e. you couldn't just ground to the frame.

I am experimenting with this in running wires for civvy trailer hookup. I will report upon success or the frying of all my electrical system.

 

[littlebob]

I know they make dual voltage alternators for boats that would give you two completely seperate systems amd a third dedicated battery for 12V. Somewhere I think I have seen an ad for a dual output for MV's, just can't remeber where. It would probabably be expensive put the best way.
Here is a link to a boat alternator :

http://www.pyacht.com/balmar-alternator-guide.pdf

 

[CCATLETT1984]

For high-draw systems like a stereo your best bet would be to mount a 12v alternator under the hood and charge a seperate battery for the 12v stuff, keep the two systems isolated from each other.

 

[FMJ]

I've still got a pile of 24v to 12v voltage converters. Mil Spec, very heavy duty 35amp capacity. NOT made overseas crap.

I'm interested in a couple as well......

 

[Ronbo]

Ok talking about having a seperate battery..Look at this siet then click on the race batteries www.voltphreaks.com . I am really into the crotch rockets too and these guys have some serious nice equipment. ( If anything just lots of good info) .

 

[TommyG45]

Two 12V batteries connected in series yeilds 24V. As we all know and have experienced in our Deuces. Now lets say you tap off one of these batteries to run a 12V load. In simple terms lets say the load on the one battery used to power the 12V load is now really reading 10.5 volts because you ran it too long. Now instead of having a 24 volt system to the deuce when you go to start it, you only have a 22.5 volt system. While this may not seem like a big deal, you need to look at it in terms of ohms law I=E/R where current (I), is determined by the supply voltage (22.5V)/(resistance of the starter motor) Just for grins, lets say the resistance of the motor .5 ohms. The most juice the battery could supply is 45 amps at the given resistance.

Lets take the case of two equalized batteries healthy and at 12 volts each. This in series is 24V. Again using Ohms law of I=E/R Current(I) = 24v(e)/.5 ohms(R). With a healthy battery set up with each battery measuring 12Volts gives 48 amps.

It may not seem like much, and there are many other aspects to consider like heat, cold, internal resistance and so forth, but I wanted to show you mathmatically why this makes a difference. In reality, the internal resistance of the winding motor on the starter may be a lot lower (short circuit) with would make for a larger delta in the numbers.

I used .5 as the example because it makes the math easy.

Tommy

 

[CCATLETT1984]

Two 12V batteries connected in series yeilds 24V. As we all know and have experienced in our Deuces. Now lets say you tap off one of these batteries to run a 12V load. In simple terms lets say the load on the one battery used to power the 12V load is now really reading 10.5 volts because you ran it too long. Now instead of having a 24 volt system to the deuce when you go to start it, you only have a 22.5 volt system. While this may not seem like a big deal, you need to look at it in terms of ohms law I=E/R where current (I), is determined by the supply voltage (22.5V)/(resistance of the starter motor) Just for grins, lets say the resistance of the motor .5 ohms. The most juice the battery could supply is 45 amps at the given resistance.

Lets take the case of two equalized batteries healthy and at 12 volts each. This in series is 24V. Again using Ohms law of I=E/R Current(I) = 24v(e)/.5 ohms(R). With a healthy battery set up with each battery measuring 12Volts gives 48 amps.

It may not seem like much, and there are many other aspects to consider like heat, cold, internal resistance and so forth, but I wanted to show you mathmatically why this makes a difference. In reality, the internal resistance of the winding motor on the starter may be a lot lower (short circuit) with would make for a larger delta in the numbers.

I used .5 as the example because it makes the math easy.

Tommy

the main issue with pulling from the center is the charging,
since you can only charge across both batteries in the deuce (cant charge individually) the battery that was reading 10.5v will get charged up to 12.6 (full charge) and the other battery will get charged the same ammount so it may be charged up to 14.5volt (overcharged). this constant over/under charging will destroy the batteries very quickly.

 

[TommyG45]

The charging system is in parallel with the series wired batteries. Voltage is constant in a parallel circuit. How can one leg of a parallel circuit ever exceed the supply voltage. Lets assume for sake of math the charging system charges @ 24 volts, it would be impossible for the two series wired batteries to ever exceed that. In your case, are you saying in theory that you really have a 27.1 volt battery when charging a battery system that has had it's center tap used? I am just trying to understand, not challenge. Can you go a little deeper to help me understand?