running dual charging systems 12V/24V

[Blitz]

Ok , I see...

Yes, You would get 12 volts. Either Positive or Negative , depending on how Its measured.

Depending on how you look at it / measure it, it would be 12 "negative" volts, using the POS lead to be the 12 volt battery, and the NEG lead to be the POS of the 24 volt bank.
( Neg - 12 volts )



Switch around, with the Negative being the 12 volt battery, and the Positive to be the 24 volt bank... and then you get a Positive 12 volts.


I know that "most "12 volt appliances do not "care" which way the voltage runs....

but this result is opposite of what I would have expected...,

and any appliance that "needs" the positive lead to be on one leg specifically, and the negative on the other leg....

could easily be reversed.

Will not reversing the voltage cause induction of corrosion ?

It seems, the positive charge would be flowing through the frame now, using the 12 volt pos post for the "positive" of the 12 volt circuit...

Which really is running the power backwards... being Negative 12 volts.

Would this positive charge in the frame not attract / cause corrosion ?
Ions attracting other ions with a reversed polarity?
opposite of how it normally lives?

This is where I get confused...

its not just the flow of the electricity from Pos to Neg,
but

when things get crossed like this... (flow and Pos or negative charges in surfaces )

are there not other issues that come about that are not "electrical" per say, but "side effects"...

Like corrosion ?
Sacrificial erosion of components not "designed " to become sacrificial?

See, I jumped to ionic attraction and probably induction as well...
as a side effect to not isolating things.

[jeeper]

Will not reversing the voltage cause induction of corrosion ?

See, I jumped to ionic attraction and probably induction as well...
as a side effect to not isolating things.

It is the plates in the battery that store the electrons. I don't see why grounding the positive would be any more prone to corrosion than the negative ground system.

You aren't really reversing the voltage. Electrons still flow from positive to negative.

[Blitz]

Yep,

Just use the 12 volt battery POS post, as the 'negative' in the 12 volt circuit. And the 24 volt bank POS post, as the positive, to get + 12 volts !

Its just counter-intuitive to me, but I guess that's just how Black Magic works : )

I would think, that if I want to connect a 12 volt appliance, I would use the 12 volt battery Positive Post, as the POSITIVE 12 volt input ...

Not so it seems.

For an easy example, a 12 volt fan ( radiator or interior cab ) or 12 volt pump... ( fuel or water ) or 12 volt Solar tracking motor...

If I connect the HOT ( power input ) leg of the 12 volt fan to the 12 volt POS battery post, and then the ground to the 24 volt POS post, my fan or pump will be running backwards.


Its just counter intuitive to me, and now I know I can ( and need to ) double check polarity. ( when I dont isolate !)

Connected correctly, it will work...
Agreed !

All this theory and Thanksgiving dinner... It pretty darn heavy.

Sometime in the next 48 hrs, I will go out to the truck, and double check my theory about motors running backwards...

Either way...
As long as I know...
wired properly, It will work.

[jeeper]

Sometime in the next 48 hrs, I will go out to the truck, and double check my theory about motors running backwards...

An induction motor may or may not run backwards when the polarity is reversed but a permanent magnet motor will.

[Desrtvet]

where might I find a 12/24 converter box Blitz?

[jeeper]

http://www.amazon.com/s/ref=nb_sb_no...%2Celectronics

[Blitz]

DesertVet,

Sorry to have made such a huge post on Your question.

This subject keeps coming up, and I just wanted to "try" to get to the bottom of it.


I know its all confusing as heck.


I like running 12 volt appliances off my stock 24 volt truck.

Obviously, I did it by isolating everything, and balancing my loads and then some other goodies that most wont care to do.

I DO have a 24 volt to 12 volt converter box on my truck.
It came with my truck, when i got it.
The only thing connected to it then and now is the 12 volt coil, for a SBC 292 engine.
Thats It.

everything else is hard wired, directly.

On the converter box in my truck,
I dont trust electronics, in an all "non electronic" Military vehicle.( one of the main reasons I got an M715 )

So I made a jumper wire, that will go from battery #1 , directly to the coil, should that converter box fail on me, unexpectedly, one day.

I wont be stranded, and the jumper wire lives above my wiper motor, ready to go.

long story short...

I dont know the configuration of Your truck, but electronic converter boxes are ....

"not hardened"

And could fail at the worst possible time.

just a heads up.

Anything You connect to the converter box, will be lost, should the box fail ( for whatever reason )

Just a heads Up.

Blitz


PS If You are gonna get a converter box, go ahead and get a big one, like 500 + watts, and maybe even a spare.

Or at least a way to jumper around it , if you use it for Your ignition, or fuel pump.

[Desrtvet]

No apologies needed whatsoever. I appreciate everyones input because as the common saying is "there's more than one way to skin a cat". I am enjoying all the knowledge that is being shared on this thread!

[Blitz]

I'm glad to hear that.

I will be the first to admit, I have a problem with what some would call "hijacking" a post.

At the same time, i figure we are all here to learn something, and open discussion is how that gets accomplished.

All of this having been discussed,
i have to say i have learned a hell of a lot from this post as well.

Its made me look stuff up and open books that have been collecting dust for too long.

And its not all related to M 715's, but its all good things to have an understanding of.

My Truck "to do" list is long.
And expensive.
And I usually work alone, and have a lot of other responsibilities, other than working on a couple of M 715's.

All that said,

My long term goal is to have a secondary alternator, and bracket for the SBC 292.

Connected to the bank of batteries that live in the bed, which are currently Solar charged or shore Power Charged.
( For a 4000 watt Inverter , self jump starting, and for running a few larger 24 volt appliances when necessary)

When I do that, I will just Isolate everything... as I have been doing, and Isolate the alternator as well.

Not that I didnt learn anything from this post, But I just have more confidence in keeping everything Isolated, at the expense of a "potential voltage drop"
with longer wire runs for the grounds and the hots. And I guess the expense of a little more wire.

I still have some questions about how things interact, when grounds are combined, and one thing we did not even touch on is
the charging voltage regulator in the alternator...

i dont know how it will react with a common ground.

it may be fine. I just really dont know "yet"...

But I do know, that If I keep everything isolated, nothing can get pregnant.

Not much else can be done, until the Mr Fusion become available in my area.

[TexasAggie]

Welcome to The Zone Texas Aggie,

A 1 volt drop in DC is a pretty big drop.

What is your opinion of "Noise" being generated in radios and navigation equipment by combining grounds?
Or electrical interference being generated by a sudden LOAD, such as a starting circuit, pulling lots of amps... and lowering the voltage on the "other" ( non starting voltage )
DC circuit?

Here is an interesting PDF I ran across ... it pertains to ... common grounds and galvanic isolation in low voltage chips and dual voltages.

http://www.ti.com/lit/an/slyt211/slyt211.pdf

First, thanks for the warm welcome. I've just been lurking around here for a bit gaining all kinds of useful knowledge. The Zone is a great resource and community.

Back to your cat skinning...
Yes, 1 volt drop is a lot in a 12 (or even 24) volt system. It won't likely burn your truck to the ground (dirt, not electrical reference), but ya might want a bigger power wire for the long term

In a truck, I wouldn't worry about any noise from combining grounds. There aren't that many sources of noise generation in a vehicle. Ignition noise and alternator whine are the classics I think of when listening to AM radio, but these are not really issues if your alternator is in good shape and your ignition system is solid. Now, if you are really into very sensitive deep-space radio gear listening for ET to phone home, I would consider that another thing entirely. I'd never worry about combining grounds for normal AM/FM/XM or any other typical automotive electrical gear.

I can understand why many boats would suggest isolated systems, many would not have such a metal frame or body like we have so much of on our trucks. I could see trying to share a common ground wire on a boat with a trolling motor and your ham radio could cause some "motor noise" in the receiver. The devices are usually some distance from the batteries and the wires will have resistance that will cause a voltage drop. The voltage at the trolling motor terminals will be less than that measured at the batteries (when the motor is running).

Having your 12 and 24 volt systems negative terminals tied together at chassis ground would not cause a 24 volt starter to affect your 12 volt stereo during engine startup.

Thanks for sharing the PDF. Yes, those are little converters used with the electronics these days (often now these are even done inside larger, purpose-built chips). You shouldn't have to worry about any of that in your truck. All of your electronic devices (of any quality) will have some basic power feed filtering to reduce the effects of noisy / imperfect input power.

All that said, feel at ease running isolated or non-isolated. Just never touch ground to hot, hot to ground or 12 to 24 and you universe should be perfectly fine