Electrical Question

[Brian Brooks]

I recently purchased a battery switch for my midyear. I have seen them installed on the negative terminal side of the battery. Will this location prevent a short of the system? I first thought that installing the switch on the positive side would be more appropriate, as to shut off all power to the electrical system. I need some input here. Which side should I install the switch?

[Chuck G.]

Re: Electrical Question

Hello Brian; All of the "thumb screw" switches that I have seen are made to fit the Negative terminal. There is a difference in size between the + and - battery terminals, and the switch will not fit over the + terminal unless you "ream" it out. I'm certainly no Electrical Engineer, but I recall that it is better to break the ground connection. Supposedly, if you break the positive connection, through some process, your battery can still "drain" as you'll still have some minor electrical "flow" over the surface of the battery. It's the same principal that we've been told for years---never store a battery on a concrete floor. Someone smarter than me might elaborate further. Chuck Gongloff

[Brian brooks]

Re: Electrical Question

Thank you!

[Robert P.]

Re: Electrical Question

Hi Brian,

I agree totally with Chuck. BTW, I have it installed on the negative side of 4 different vehicles. It gives me peace of mind while they are parked, especailly the vehilces stored inside.

For the solid axle cars the disconnect switch is NOT recommended unless the system is polarized after reconnecting. This was discussed in a seminar by John Pirkle, Jr at the Carolinas Chapter meet in Banner Elk, NC..

Hope this helps, Bob

[John Waggoner]

Re: Electrical Question

Bob,

Would you elaborate on the solid axle polarization? I have use one of these switches for the last couple of years on my 62 with no ill affects, that I know of. Am I tempting fate? What do I need to do to check for polarization, or lack there of?

[Robert P.]

Tempting fate (yes)

Am I tempting fate? What do I need to do to check for polarization, or lack there of?

Hi John, sorry for the alarm, but according to JP,Jr you are doing just that (tempting fate) and probably to an '002 regulator (matter-of-fact, thats exactly what he said). The gist of the siminar was, it would eventually cause the regulator (as I recall) to fail. He said it could happen after a few disconnects or after a large number, but eventually it would.

Its been years since I polarized anything so you will need to refer to your shop manual on the procedure...

Perhaps others have opinions...... I'm simply passing along what he said and IMO he should know.

Bob

[J Grantham]

Re: Electrical Question

I have a 62 and installed the knob disconnect two years ago. I have never polarized the generator field after the first time (when the generator and voltage regulator were rebuilt). Why do I have to polarize each time I turn the power back on? Nothing has been reversed. I don't want to abandon the switch but I want to undersatnd whats going on here. Help please......

[Jack H.]

Re: Electrical Question

Electrical engineer responds!

Doesn't matter what side of battery switch is installed taking into consideration the difference between alternator and generator systems that is wisely mentioned in other replies. Open circuit is open circuit. Current's gotta find a path from +battery terminal to -battery terminal to run. Since switch is installed on the battery terminals themselves and earth ground is meaningless (car is insulated by rubber tires), any open circuit opens and shut's down the entire system.

Now, let's talk about important stuff!!! Most of these switches (not all) are the Made in Taiwan jobby with green plastic screw handle for contactor. There are other styles (knife switch) out there that I'd prefer to see based on how the contact is constructed.

In the screw jobbie, there is no tactile feedback as to when you've made a good solid switch open/close. Typically, you're in a hurry and slightly afraid of over tighten the switch. Kiss of DOOM!

100% of your electrical current flows through this switch. We're talking about a 12VDC system where an ohm or two that wasn't planned can raise havoc. If the switch isn't firmly/fully closed, you'll get contact bounce. This will cause internal arcing.

The cheapie Taiwan switches I've seen fail (some on the road at freeway speeds!) have a VERY small contact surface area and VERY low thickness of copper/brass plate. When they arc, the plate goes 'bye bye' and 'funnies' start happening (hard to crank, alt/regulator doing squirrley things, intermittent engine cut out)....

Consider these switches sell for $3-20. Then, compare to the cost of a professional assy as used on the race circuit. You'll see you're getting just what you paid for!!!!

Next, think what happens if the ohmic contact errodes and you develop high resistance inside the switch. If it's on the positive terminal, you'll drop some IR and the voltage regulator will see (sense) an absolute battery voltage that's lower than true. Conversely, if the switch is high resistance and it's installed on the neg terminal, the IR drop across the switch acts to push the battery off true ground and the charging systems sees a battery that's higher potential that it actually is!

Lot's of stuff is based on knowing the ABSOLUTE B+ profile the battery should have. If your el cheapo cutoff switch isn't working like it should you can see some pretty hilarious electrical 'funnies' that's love your time/wallet.

So, if you gotta use one of these guys, screw the contacts closed with 'gorilla' strength. And, when you open the switch, unscrew the plastic wheel ALL THE WAY OUT....

[J Grantham]

Re: Electrical Question

Jack, Thanks for the circut review and the effect the switch can have on the regulator from an over or under voltage standpoint. However, I still don't understand the polarization question. I understand that a new or rebuilt generator needs to be flashed to establish polarity but why would this have to be done every time the power switch was turned back on? Should I be flashing the field every time I take a battery terminal loose? I am not an electrical engineer or an electrician. More explanation please.

[Jack H.]

Re: Electrical Question

Generator is simple DC motor run in reverse (motion produces electricity instead of electricity producing motion). This is NOT true of alternators. Don't remember what year car we're talking here as generator went 'bye bye' on Corvettes in '63....

If you're old enough, you may remember dad's first electric razor with a thumbwheel on the side. You plugged it in and gave the thumbwheel a spin to make the motor run in the desired direction. If perfectly balanced, it could spin either way....

Same effect with generator. Without 'polarization', motion turning the generator armature 'could' produce output voltage either upright or inverted with respect to ground. So, the process of polarizing a freshly rebuilt generator was done to leave a residual magnetic field to 'bias' generator startup/output in the correct polarity sense.

Yes, you can lose polarization if battery B+ is left off generator for PROLONGED periods of time and/or the gen experiences an electrical 'distrubance' absent its stator field (BAT terminal connection). Bottom line, if you're only disconnecting for short periods of time (link on the show field), simply tain't a cognent concern. If you're disconnecting the battery for extended periods of time (months/years), pros take no changes and follow the polarization proceedures defined in the shop manual.

[John]

Re: Electrical Question - Polarizing

When I bought my project '57, it had sat in an old wooden garage for 14 years without ever being run; when I hauled it home and oiled-up the engine to start it for the first time in 14 years and drive it around the subdivision to see if there were any obvious mechanical problems, the ammeter showed a full 30-amp charge, even with a new fully-charged battery, and when I got home, the generator was VERY hot. It had been so many years since I had a car with a generator (instead of an alternator), I had forgotten about polarizing. When it finally dawned on me, I pulled out the old shop manual, polarized it, and it worked like a charm.