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Ed (Ont) 
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Joined: 08 Nov 2009
Location: New Lowell, Ont
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 Topic: Charging 8V battery
Posted: 26 Jan 2026 at 4:05pm |
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My friend dropped off an 8V battery out of a 1946 Ford that someone had installed. What is best way to try to charge this? I have several chargers but nothing 8V. I think the battery is no good. I will check voltage of it first and go from there. Thx.
Edited by Ed (Ont) - 26 Jan 2026 at 9:37pm
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WF owner
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Joined: 12 May 2013
Location: Bombay NY
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Posted: 26 Jan 2026 at 4:13pm |
You should be able to charge it with a 12-volt charger on the lowest setting, without hurting anything.
Several battery chargers had a single setting for "12-volt low - 6-volt fast charge".
Edited by WF owner - 26 Jan 2026 at 4:15pm
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steve(ill)
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Posted: 26 Jan 2026 at 4:19pm |
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and if you have a volt meter, connect it across the terminals and monitor as the battery is being charged with the 12v charger..
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Like them all, but love the "B"s.
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Ed (Ont)
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Posted: 26 Jan 2026 at 5:01pm |
Thanks guys! 
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DSeries4
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Posted: Yesterday at 4:21pm |
I was just talking to my starter and alternator repair shop a few days ago and got on the subject of 8 volt batteries in 6 volt systems. In short, they DON'T work! The maximum output of a 6 volt generator is only 7.2 volts, so the 8 volt battery will never get fully charged, instead it keeps draining.
A 6 volt battery with a 6 volt electrical system that actually WORKS is a far better choice - a good working generator and very thick battery cables.
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'49 G, '54 WD45, '55 CA, '56 WD45D, '57 WD45, '58 D14, '59 D14, '60 D14, '63 D15D, '66 D15II, '66 D21II, '67 D17IV, '67 D17IVD, '67 190XTD, '73 620, '76 185, '77 175, '84 8030, '85 6080
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Les Kerf
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Posted: 21 hours 39 minutes ago at 6:26pm |
 DSeries4 wrote:
I was just talking to my starter and alternator repair shop a few days ago and got on the subject of 8 volt batteries in 6 volt systems. In short, they DON'T work! The maximum output of a 6 volt generator is only 7.2 volts, so the 8 volt battery will never get fully charged, instead it keeps draining.
A 6 volt battery with a 6 volt electrical system that actually WORKS is a far better choice - a good working generator and very thick battery cables. |
Actually, they work well enough that Allis-Chalmers offered it as standard equipment on the W226 Power Units.
It is a simple matter to adjust the Third-Brush type generators to properly charge an 8 Volt battery, my late Father-in-law ran his WD this way for decades with no ill effects.
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steve(ill)
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Posted: 21 hours 32 minutes ago at 6:33pm |
a 6 volt generator NOT CONNECTED TO A BATTERY, will put out about 14 volts... A 12 v generator NOT CONNECTED TO A BATTERY will put out 28 volts... I have measured that several times....... The BATTERY is the SINK or REGULATOR for the gennerator.... So when you connect a 6v generator to a 6v battery you will get 7.2 volts or so..... Connect that same generator to a 12 volt battery and it will be around 13 volts...
The BATTERY is more or less a REGULATOR of the voltage.... remember the old days when they said "dont pull the battery terminal off when truck is running" ??... you can blow out the head lights or other equip when the generator voltage SPIKES..
You may not get a lot of CURRENT or AMP output... but you will get a lot of VOLTAGE.
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Like them all, but love the "B"s.
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55allis
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Posted: 17 hours 28 minutes ago at 10:37pm |
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If I’m understanding this correctly someone could run the old 6v cutout on a 12v battery without any issues?
I’ve got a 45 gas that had the 6v cutout until I put a 12v regulator on it that was apparently a dud, it don’t charge worth a crap anymore.
It did charge for a bit so I’m guessing something burned out inside.
I never knew a 8 volt battery existed for a car…
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1955 AC WD45 diesel with D262 repower, 1949 AC WD, 1963 A-C D17 series 3, several Allis garden tractors 
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Steve in NJ
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Posted: 15 hours 27 minutes ago at 12:38am |
In most cases, an 8V Battery is a bandaid. You're much better off purchasing a 6V Battery for your 6V system. Just make sure the Gennie is setup on the money and you won't have any problems. In the time the Tractor isn't used, keep a Battery tender on it to keep the Battery "active". You'll get a lot more longevity out of the Battery, and when you need the Tractor, the Battery is fully charged, ready to rock n' roll, and the Tractor fires right up. If you use the Tractor in the Winter months, make sure you install a lighter oil for the cold Winter months.. HTH Steve@B&B
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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steve(ill)
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Posted: 8 hours 2 minutes ago at 8:03am |
Gavin, its not a good idea to try to make a cutout work on a 12v system. Its not the cutout that is the problem, its that your trying to use the light switch resistor as a current regulator.. This is all OLD SCHOOL, very simple system for a very old 6v tractor.. If you go to 12v it is much better to get a real Voltage Regulator and eliminate the cut out and the light switch resistor.... that being said, i have never TRIED to use the cutout and resistor on a 12v system.
The problem some people have is if you use the ORIGINAL 6v generator to put out 12v, you have very little current. You need to get a regulator rated for 6 or 8 amps ( or similar).. If you use a 30 amp regulator that was made for a 12v car its bound to have some problems... Regulator needs to somewhat match the generator.
Edited by steve(ill) - 7 hours 59 minutes ago at 8:06am
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Like them all, but love the "B"s.
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Les Kerf
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Posted: 5 hours 50 minutes ago at 10:15am |
55allis wrote:
If I’m understanding this correctly someone could run the old 6v cutout on a 12v battery without any issues? … |
That may be pushing your luck a bit.
The 6V cutout has small diameter shunt windings that are used to energize the cutout relay which connects the generator output to the battery and thus the rest of the electrical system. These windings are designed to withstand a certain amount of current and also be able to dissipate the heat generated by this current.
Ohm's Law tells us that if you double the voltage across a fixed resistance you will get double the amount of current. Ohm's Law also tells us that Power (Watts) = Volts x Amps.
When both Amps and Resistance are known, the formula for Watts is P = I^2 x R.
If we double the amount of current through the shunt windings, we increase the Wattage by 4 times; this quadrupling of the heat generated in the windings MUST be dissipated somewhere, and if not, it may well burn out the windings.
I was unable to find a decent diagram of a 6 Volt cutout, but they look exactly like the cutout relay shown in the Shunt Winding shown in the dotted red lines below.
Edited by Les Kerf - 5 hours 47 minutes ago at 10:18am
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