8-VOLT battery use

What that Gentleman told ya is basically correct, but as Paul Harvey might say, heres the "Rest of the Story"

Its true a genny cant pump current into a battery to charge it UNLESS its of higher voltage then the battery, and an 8 volt battery would be 8.4 volts fully charged (4 cells at 2.1 each), Its also true its possible to tweak up a Voltage Regulator for use on an 8 volt system so it will perform better.

HOWEVER Im not sure that an unmodified Voltage Regulator coupled up to a 6 volt Generator might still not be able to charge the battery, although maybe not as high of a charge rate. My opinion is based on the reason that once the genny starts to rotate, it will self excite to some extent due to the residual magnetism in the iron field poles REGARDLESS ITS CONNECTED TO THE BATTERY VIA A CLOSED CUTOUT RELAY YET. And thennnnn nn if its output voltage rises to a sufficient high enough level to close the Voltage Regulators Cutout Relay ???? THE BIG QUESTION???? its exposed to battery voltage which (being higher then 6) will put even more current through the gennys field windings (then it would at 6 volts) which means its output is now increased above what it would have been if there was only 6 volts forcing current through its field windings.

Basically, a genny dont necessarily know what voltage its supposed to produce, its increased if it turns faster and/or theres more field current. The Voltage Regulators job (its internal field control relays) is to control and limit that field current so the battery charges BUT DOES NOT OVERCHARGE. In addition, its cutout relay must close when the gennys voltage rises on its Arm terminal so the gennys output can get to and charge the battery (the BAT terminal on VR) but open otherwise so the batterY dont reverse discharge when the tractors off.

Again, Im NOT saying it not possible and indeed agree its best if the VR were adjusted up for 8 volt charging. Im just questioning that even if NOT adjusted it still couldnt charge an 8 volt battery, although maybe not as many amps worth.

I would think the different types of Voltage Regulators and whether they are 2 coil or 3 coil (if they have both voltage and current regulation) would make a difference, but I suspect some types of VR will still work to charge an 8 volt battery while other types may indeed NOT.

Talk to that Gentleman n see what he thinks??? Make sense ????? ?? lol

Take care yall n God Bless

John T Nordhoff in Indiana

A voltage regulator limits the maximum voltage that the generator can put out by limiting the field current when the voltage rises high enough to open the over voltage relay contacts. The maximum output voltage is set by the spring tension on this relay.

There are three versions of "regulator" on older equipment and cars. The first is the cutout relay. This is simply a relay that disconnects the battery when the generator is not producing any output in order to prevent the battery from discharging through the generator windings. Generator output voltage is a function of generator speed and field current. Generator output current is limited by the internal resistance of the wiring (and the position of the third brush for a 3-brush generator).

The second version is the two relay type, which adds a voltage limiting relay to the cutout relay. Instead of having an external switch to control field resistance like some tractors, this approach uses a relay to short the field resistor. This relay opens at a pre-determined voltage to add field resistance, limiting the maximum output voltage. Maximum current is still limited by the generator itself.

The most "modern" 3 relay type adds a current limiting relay, which also puts extra resistance in the field circuit when the maximum current out of the generator exceeds a preset level. This allows lower resistance windings to be used in the generator, reducing heat and improving efficiency.

A generator with only the cutout relay will charge to a higher voltage like your example above (assuming its spinning fast enough), but at a reduced current due to the resistance of the generator windings (lower current = less loss in the windings = higher output voltage). Either of the other two regulated types will only charge to the maximum voltage the overvoltage relay is set at.

Since lead acid batteries charge to a constant voltage, a regulator set to the proper value for a six volt battery will never fully charge a eight volt one.

I have a ca 1960 Motors manual that has a very good discussion of generator and regulator operation and repair/adjustment procedures. Unfortunately, its in the shop and its way too cold to walk out there to get it tonight. If you have additional questions, post a new thread & I'll see if I can dig out the answer. May take a few days to respond, as I'm working 7 days a week for the next couple weeks.

Keith

I was thinking the original poster at least had a VR instead of a Cutout Relay but unsure if a 2 coil or the later 3 coil with BOTH Voltage and Current Regulation??? If he can get more current to flow through the field windings that increases the electromagnetic field strength and the gennys output is increased.

The other critical question to me (per my post) is still if the cutout relay portion of the VR will ever get closed (closes once the gennys output is some higher then battery and is adjustable) cuz once its closed the gennys field sees 8 volts which pumps more current through the field then if it saw only 6 volts and theres more output.

DO YOU THINK IF A VR WERE UNMODIFIED AND HOOKED TO AN 8 VOLT BATTERY, THE CUTOUT RELAY PORTION OF A VR WOULD EVER CLOSE????? ????? ????? I posted it depends on the type of VR and I still think thats relevant to answering this question cuz I feel it has to close so the field sees 8 instead of 6 volts which increases the field strength (more field current) to cause increased output...

I dont have any specs or data or books on those systems, if you come up with some good basic info I would appreciate a copy, please let me know

Fun discussion, tale care Keith

John T Nordhoff in Indiana jmn50@msn.com

I reckon I understand and always agreed how the simple 2 wire cutout relay might suffice to charge an 8 volt battery and still see how the Voltage Control Relay in a 3 coil VR (has BOTH voltage and current control relays) might prevent charging an 8 volt battery if unmodified,,,,, ,,, BUT STILL NOT SURE how a 2 coil (current regulation only) is going to behave. I know they (2 coil VR with current control but NOT voltage control) are not used as much and may be the older style, but Im thinking they would me more apt to work UNMODIFIED to charge an 8 volt battery then a 3 coil (voltage PLUS current control) relay may do.

Whats your thinking on the 2 coil versus 3 coil Voltage Regulators as to the ability to charge an 8 volt battery with NO modifications. Its basically ONLY the 2 coil VR's that Im questioning ????? ???

Fun discussion, thanks

John T (Long retired and rusty Electrical Enginer)

I have a 1956 Willys pickup that had an 8 volt battery in it when I got it. I reset the regulator for a six volt battery, & have never had any problems getting it started.

An 8 volt battery was a quick & dirty upgrade. Agree that you'd be better off to either stick with the 6 volt system & make sure everything works like its supposed to, or upgrade to 12 volt.

Keith

John T