Negative Voltage

spark-station; i can not think of an American manufactured automobile that uses pos + as a chassis ground, all the one I've ever seen since the early fifties have gone to 12 volt neg- ground or frame. i believe the next step is to go to 36 /42 volt batteries to allow electrical operated valves perry

Hi Sparky,

Actually the standard for US, European and Asian automobiles has been negative ground for about 5 decades. The UK was slow to change, and made some positive ground cars into the 60's.

Sparky,

You are in New Zealand and speak yet another version of English as opposed to the Brits and us Yanks so perhaps what is confusing me is a language difference in connotation.

Here in the states we used to connect the positive battery terminal to the chassis, i.e., positive ground.

Now we connect the negative terminal to the chassis, i.e., negative ground.

What you appear to be saying is the opposite???

Surely its only a matter of syntax?

As for the telco batteries. You are right about that but you don't ever, if they still exist, want to come across the output from a ring generator. But I'll bet you knew that.

They used to sell as military surplus, on Canal Street in Manhattan, the hand crank ones from field phones. As kids we used to buy those and ask our friends to hold the wires while we cranked the handle.

As for the new cars with 2 12 volt batteries. Are you saying they are connected in series for 24 volts or in parallel for higher capacity?

j.

Hello Jack Jersawitz

2x 12 Volt batteries connected in series for the 24 Volt supply to all the vehicle electrics.

If you need a 12 Volt supply in the vehicle, you can either tap off from the battery midpoint (bad idea because of unequal usage of batteries in series), or fit a DC/DC Converter, 24V DC to 12V DC.

These DC/DC Converters are now quite cheap, and I use an 8 Amp @ 13.6 Volts DC output for one in my truck (Running a transceiver and car stereo), and a 30 Amp @ 13.6 Volts DC for use in the home, charging a couple of 12 V car batteries outside the window, which running 12 Volt transceiver, emergency equipment, etc in my office.

The NATO specification calls for vehicle electrics as 24 Volt systems, and the 24 V system is used extensively in Canada, Northern Europe, and Northern Japan, because of cold conditions during Winter.

Kind Regards....

Hi Spark... I couldn't agree more with you... (And, Jack, I perfectly understood what Spark said... maybe because I'm not American too... ...)

Some more infos: in older times of telephony the voltage of "60V" was used (5 batteries of 12V) just because "60R 1A" relays were used (in the older exchanges) for dialing and connection purposes... Later (in modern telephony) the exchanges became "electronic" so there was no more need for such a high current... So, the voltage was reduced to "48V" (4 batteries of 12V) which is a harmless voltage level but, also, appropriate for the telephony operation...

Concerning the connection of the "+" terminal of this voltage to chassis: Of course it is so, because the corrosion of the metal is lower... But my question is "why???"... I've heard that if you connect the chassis to the "-" terminal then its metal structure loses electrons and that's why its mass is reduced... But why the metal loses electrons???... Is it because of its "negative potential"???... But in reference to what??? (obviously not in respect to the "earth" because the chassis is, also, always connected to the "earth"... maybe in respect to the sorrounding atmosphere???... ...) Is this the correct explanation for the observable corrosion???... Any ideas???...

Thanks alot for your answer. You have given some insight on the origin of -ve voltage which I admire. I have picked the phrase below as a lesson learnt

"To sum up, using the -ve as the ungrounded/not connected to chassis supply wire, gives minimised chassis and frame corrosion."

Thanks

indeed, communication system use -48v is for the aim of reduce corrosion.

Concerning the connection of the "+" terminal of this voltage to chassis: Of course it is so, because the corrosion of the metal is lower...

It is not so, and has not been so for many decades. The last widely available cars in which there was a "connection of the "+" terminal of this voltage to chassis" were from the UK in 1967. You can verify this by a simple look at your battery. The terminals are clearly marked, and you will see that the negative terminal (marked with - ) is connected through a heavy wire to the cars chassis. Unless your car has been modified, this wire is black in color. The other wire, usually colored red at (at least) its termination at the battery, generally heads to the starter motor's solenoid, and frequently has a fusible link or fuse and perhaps a branching connector for certain loads that must have power available at all times.

In the 1950's and before, positive ground (+ terminal connected to the chassis) was common.

Hi Ken... You are absolutely right about the cars... But in my previous post I refered to telecommunication equipment, not cars... I.e. in all our telecom devices (that we design and produce as a company) we always connect the "+" terminal of the input voltage (48V) to the chassis of the device... And we do so because of the lower corrosion... And my question is "why???" (go back to my previous post to see what I mean)...

So... Any ideas???... ...

I'm sorry, I'd thought the part of Sparky's post you could not agree more with was the part about automotive grounding. Had I read your post more carefully, I would have seen that you were writing specifically about telco equipment.

re the corrosion: hmmmm. The same reason is postulated for cars going to negative ground and telco equip being positive ground. I'm not sure that I can say anything that makes sense. The fact that the car chassis is pretty well insulated from "earth" potential could make the two situations different.

I suppose that in the typical car situation, the wiring is copper and the chassis is steel, so the steel galvanic potential is more negative by about .4 volts. So maybe that means that the combination of galvanic potential and battery potential is lowered with negative ground. Maybe in telco equipment, the lead vs copper potential (about .2 v the other way) at the battery terminal is the more critical? Or maybe I have it reversed. Or maybe my theory is completely wrong.

I surfed around a little and found this. It seems to make sense.

Yes, Ken... Interesting article and it makes sense...

So, we have the two following situations (assuming that the chassis is always connected to earth):

1) If we have the (-) terminal grounded then positive ions are removed from the exposed wires with positive voltage potential (or even from corresponding insulated wires due to imperfect insulation) and are putted down on the sorrounding wet earth (as the earth has negative potential). So, these wires lose ions, hence they lose mass (corrosion). [In this case, by the way, we don't have any similar problem with the chassis metal, because chassis and earth have the same (negative) potential.]

2) If we have the (+) terminal grounded then there isn't such a problem, because the wires with positive voltage potential (or the chassis metal) have the same potential as the sorrounding wet earth (no ions leave the metal, no corrosion happens). [Moreover, we don't have any corrosion of any other wire with negative voltage, as its potential is more negative than the potential of the earth.]

Do you agree with the above conclusions???

Yes, sounds good to me.