6v + grnd versus 6v - grnd in regards to onboard 6v-12v step up converter

[3046moparcoupe]

A couple questions please - in regards to battery and ground architecture for my P15 project.

 

1): I've replaced the vacuum wiper setup with the Newport electric 12v kit, ( Newport unit is installed under the dash waiting for wiring).

 

2): I'm 90 % finished building a complete new wiring harness, ( using my old original harness, and the P15 shop manual electrical wiring diagram as a guide. )

 

3): I have 2ea generators, both have been restored (new bearings,brushes, cleaned up and painted), and checked out by Fort Worth starter and Generator. (so I've got a good working and a spare generator should I need it).

 

4): I'm planning on leaving the car as 6v battery, so the wire gauges in the harness have been sized properly for the higher amperage, and I'll be purchasing a 6v cranking battery.

 

5): I was planning on connecting the cranking battery up as 6v positive ground, ( like it left the factory), just seems to make sense to me - then there's no conversion in your head when your working through your electrical issues in your shop manual, etc...however, either way ( 6v + grnd or 6v - grnd) is certainly acceptable, ( if it makes sense to go the other route and connect the cranking battery up as 6v negative ground )...this basically is where my question lies:

 

My understanding, (from what I know about dc power and mostly from what I've learned here on the forum), is that beside from the orientation of the cables coming off your battery, you've got the following minor issues to also get in order:

 

a): the + and - connections on the coil have to be in agreement.

b): the input side of your ammeter gauge has to be wired in agreement.

c): the old original 6v radios WILL NOT work either way, they have to be 6V positive..(not an issue for me)

d): your voltage regulator has to be polarized in agreement to work with either the pos or neg setup.

 

I am not aware of any other issues that would apply to any of the cars working parts, (starter for example),..you've basically just got current flowing from one wire/batt, through your device, and on and through your second wire/grnd...same amount of current, amps, etc...either way, device doesn't care....

 

Finally - here's the meat of my question,..(unless anything I've prefaced above is not correct, then please step in regarding the above as well)…

 

I need to get a 6v - 12v step up converter to run the 12v Newport Electric windshield wipers. Began reading up on them and pricing them today. Newport says the wipers should draw around 4 amps max. Some of the step up converters say they will operate with a 6v negative or a 6v positive system, and some converters don't say if they will or if they won't....they all seem to show the same basic configuration, 2ea wires in 6v + & -, and 2ea wires out 12v + & -.... I know that not all the old cars were 6v positive, some were 6v negative,..and with these power converters being listed as converting 6v to 12v it makes me think that it might not matter, just connect up your step up converter to your 6v system and the input current will either flow through from positive to negative or vice versa with the converters functioning correctly either way. ???  I am assuming here on this, so I may be 180 degrees wrong,...definitely looking for help with this...also my Newport wiper kit instructions do not say anything more than 12v operation only,...(which in my head means 12v negative ground since there really is no such thing as 12v positive ground),...however again, it is just an electric motor, like the starter motor,...and in my head, seems like it shouldn't care...the current just needs to pass through the device. The Newport wiper system does get it's ground through the case of the wiper motor housing...which bolts to the underside of the dash. This concerns me as well. Initially in my head I thought it would be a MUST - to keep my 6v + common ground of the car SEPERATE from the 12v - ground of the Newport wiper motor, so I would need to make sure the wiper motor bracketry was completely isolated from the chassis of the car, and run 2ea dedicated wires (+&-) over to the unit, then I decided it might just be easier to set up a 6v negative ground system,and have a common negative ground, (then unless I misunderstood what I was reading, I seemed to find previous posts here on the forum stating that it was OK to share a 6v + grnd with a 12v - grnd, (just don't let the hot sides ever come together) ???

 

lastly, when I got this old car, someone had added an aftermarket gas gauge (which did not work),..after some study, I discovered that the sending unit in the tank was in-correct (single wire type), I purchased a 2 wire type, cleaned up the points on the gauge, connected the 1 & 2 terminals between the gauge and the sending unit, added -6v battery at the ignition terminal ,..and the gauge works perfectly,....I can't see how changing the hot wire into the gauge at the input (IGN) terminal could affect t he operation of the fuel gauge, but I seemed to read on here where someone thought it might, if anyone out there knows the answer to this, now would be the time for me to know, as I'm fixing to install the new sending unit I the tank, etc...and I definitely want the original fuel gage to work, as I have it doing now.

 

Thanks in advance AGAIN, I hope you electrical wizards out there are listening...can't tell ya how much I appreciate the help and the education received here on the forum.

 

Steve

 

 

 

 

 

[maok]

If the Newport wiper system is -ve ground then it would be best to set your car up as -ve ground 6volts, (or just go -ve ground 12 volts and step down to 6volts where you need it). It would be very tricky to isolate the wiper system from the ground connections.

 

The amount of current draw will depend on how smooth the wiper system operates. Once you have resistance to the movement of the wipers your current draw increases.

[DonaldSmith]

My understanding is that the 6 to 12 volt converter doesn't care whether the 12-volt circuit is positive or negative ground, or grounded at all.   

 

The only oddity is that, if you happen to connect the 6-volt and 12-volt "Hot"wires, you will get either 6 or 18 volts, depending which way the grounding happens to be.  But you will be keeping the "hot" wires apart anyway.

 

 

[3046moparcoupe]

THANK YOU Maok and Donald both for your reply's on this.

 

Donald I was reading through the forum last night until my eyes finally crossed :), Don Coatney had some good past posts on here, I especially liked the one where (if I observed it correctly, again I had been searching for hours and was a bit fatigued to say the least), anyhoo - he showed an engine with both a 6v generator system and a 12v alternator system,...and if I understood correctly, his point was that ground is ground,...made me try to think past the norm of what I've always dealt with in a typical 12v DC system, where you sure don't wanna get + & - crossed up...and I visualized taking my voltmeter and going from any ground on a 12v system to any other ground with your red and black leads from the voltmeter, you are going to read "zero"...so why wouldn't the common ground work ? even if it's + or -, or across 6v or 12v,...it's still just ground,...seemed to start trying to make sense in my peanut head.

 

So my thinking was moving towards being in line with your reply above Donald Smith, but I gotta say you have sorta lost me with the last four words of your reply there "or grounded at all ?"

 

If you can further paint me a picture I'd appreciate it..:) 

 

I may try sending this reply in a message over to Don C..to try and get his guidance as well on this,...so I'm thinking - to recap,....that the overall chassis ground of my pos 6 v system would be fine to share (and also provide the ground), for an accessory (12v wiper motor) being powered from a 6v-12v step up converter, since I'll be running a dedicated 12v output power wire from the step up converter to the 12v wiper motor..?? My ground for the 12v wiper motor can be - or +, and can be shared with the overall common chassis 6v+ ground of the car, with no ill effect ? (burnt wires, paint, parts, smoke test ).

 

Steve 

[DonaldSmith]

I've got a 6-12-volt converter in my car, to power outlets for cell phones, GPS, etc.  The converter magically produces 12-volt direct currrent, with (+) and (-) posts.  I figured I had better have the (+) go to the center of each outlet, and the (-) to the shell, in case anything I plug in is polarity sensitive.  But the power outlets are not grounded to the car.  Everything is happy. 

 

Is a 12-volt wiper motor polarity-sensitive?  I don't know. But to be safe, ground the shell to the (-12 V) post and run the "hot" wire(s), through switches, fuses, etc., to the (+12 V) post. 

 

("Hot" wires are any that, if touched to ground when powered, will spark.)  

[maok]

No you cannot have a positive ground and negative ground together.

 

You can have 6v positive ground and 12v positive ground together.

 

Or 

 

You can have 6v negative ground and 12v negative ground together.

Edited June 28, 2018 by maok
error

[rhelm1953]

I used the Newport engineering wiper motor in my 1950 Plymouth with 6V +ground and used the Newport 6 to 12V power inverter.  I followed the wiring instructions and it works like magic.  I did not have to isolate the wiper motor from chassis ground and I have +12V available to power a usb charger and a little Bluetooth amp so I can play tunes from my phone.

 

 

[3046moparcoupe]

thanks rhelm1953, I appreciate the input big time....I looked at the very same unit you show in your reply, and I also found the same unit over at vintage auto garage for about $5 cheaper..

looks like it's made in New Zealand, has a 1 year warranty and has to be shipped over there for repair if necessary....installation notes talk about how warm the unit gets (I noticed it has the onboard fan and others on the market do not),..also states that it's not water proof, and others out there seem to be encapsulated so they are waterproof (not that I'm planning on getting it wet by any means),..anyway - other step up converters out there are way cheaper, and I'm suspect that they will do the very same thing as this unit will,....trying to learn here, knowledge is our friend

 

I'll keep diggin on this, read an article last night on the HAMB, where folks were saying as far as the grounds go, it doesn't matter, they can be mixed,....they made reference to the very computer I'm typing on right now,..they said there are all kinds of voltages present and working inside our computers and also a mix of + and - grounding,...also visited an electronics web site where a previous person has asked the very same question, can +6v grnd and -12v grnd be connected,..and the reply back was absolutely YES...

 

I've been pretty nuch a one way valve on this forum the past few years (always needing help and asking questions), I'll definitely post my finding when I get to an absolute 100% sure answer on this , in effort of sharing and helping others on this forum.

 

Steve

[3046moparcoupe]

maok, thanks for the reply,...in reference to your last sentence  "You can have 6v negative ground and 12v positive ground together. "

 

I believe maybe you meant to say:

 

You can have 6v negative ground and 12v negative ground together.

 

Correct ?

[Don Coatney]

As I have said many times before.

 

 

 

On any DC circuit the loop must be complete to both battery poles for anything to function irrelevant of ground polarity. It is possible to have a dual voltage automobile as pictured below with both a 6 volt positive ground generator and a 12 volt negative ground alternator both systems sharing a common ground.    

 

 

[maok]

2 hours ago, 3046moparcoupe said:

maok, thanks for the reply,...in reference to your last sentence  "You can have 6v negative ground and 12v positive ground together. "

 

I believe maybe you meant to say:

 

You can have 6v negative ground and 12v negative ground together.

 

Correct ?

 

Yeah, sorry that was a typo. I have edited my post.

 

 

[3046moparcoupe]

Here's a link to an electronics web site I found that is in agreement with Don's post above...

 

I'm here to learn, and man oh man are you guys here on the forum helping it happen... thank you...knowledge is an awesome thing.

 

http://electronics.stackexchange.com/questions/315208/can-a-6-volt-positive-ground-system-share-a-common-chassis-ground-with-a-12-volt

 

The fella who was asking this question on this electronics forum web site, was wanting to put a modern 12v gas gauge in an old 6v pos grnd car. So a little bit different than my application, but still dealing with the same basic subject. When I first stumbled across this web site, and read the question and answer to this, what I got from it was YES, I felt like I was absorbing everything the instructor was saying, but sometimes it just takes missing a single word, to get in trouble with stuff like this....for example, I finally discovered this evening - why some folks will say that reversing the polarity to a starter will cause the starter to change directions and other folks will say that it won't,...the answer is that "they are both correct", some starters it will and some starters it won't, from what I've read - it turns out that older starters that used field coils are not affected by a polarity change, however newer starters that use magnets rather than field coils will be affected.

 

So there can so easily be a catch to all this..

 

e

the following is a cut-n-paste from the link above, and shows the diagram and some short verbage that the tech used to illustrate and answer the question...

Then the last paragraph, was an additional comment from another individual who was stating that this also worked for him,....course, anyone can type anything on a computer screen that they care too,...still doesn't mean it's correct.; But with Don C's replay above, in conjunction with this link/below that I stumbled across and found, I'm thinking we have good solid accurate information here, on this...

PLEASE, IF I'M MISSING THE FOREST FOR THE TREES HERE, WITH ANY OF THIS, PLEASE - YOUR INPUT IS APPRECIATED AND DESIRED. JUST LIKE YOU - I WANNA LEARN AND IMPROVE.

======================================================

As you found out yourself, you need a inverting voltage converter for that.

-6V → +12V. They share the same ground level.

^{simulate this circuit – Schematic created using CircuitLab}

And the answer to your questions is: yes, sure.

EDIT, as asked for in the comments:

There is nothing special about ground other than we define it to have a potential of 0V. It's just a reference potential. And voltage isn't more than the difference between the potential of two points in the circuit.

So, this -6V is a property of the in wire and this +12V is a property of the out wire. Ground does not see anything what's going on on other wires.

I purchased an inverted voltage converter (-6v input - 12v+ ouput) and connected all of the grounds to the chassis and it worked perfectly. THank you Janka and Hlovdal. I really appreciate all of the input. – Jim Stevens Jul 13 '17 at 21:54

 

 

Edited June 29, 2018 by 3046moparcoupe

[DonaldSmith]

One last lash to a dying horse.  The major purpose of a ground in automotive wiring is to save wire.  A wooden boat has a separate "neutral" wire running daisy-chain from item to item, in lieu of "grounding" each item to a metal body.  The invertor shown in the previous diagram grounds both circuits to the case, saving wire.  My inverter is not grounded, but has two separatde wires for each circuit.   

[3046moparcoupe]

Many thanks Donald, I really appreciate your patience and efforts to help me here on the forum...you have stepped up on just about every post for help I've made … and this time was certainly no different. I hope it all goes your way today

 

Steve'o

Edited June 29, 2018 by 3046moparcoupe