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6V battery charged at 12V


Max4Me
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I use a battery tender on my 1925 Maxwell when it's not in use. The tender is set for 6V charge for a 6V battery. Unfortunately, we had a power outage and unknown to me when the tender came back on, it defaulted to 12V charging. Fortunately, I am a neurotic so I always disconnect the battery cables when the car is garaged, so the electrical system is safe. I figured the battery was toast, however, using a voltmeter, the battery shows a charge level of 6.59 volts. Did it survive being charged at 12V or is my meter lying? Is the battery safe to use with the 6V system or should I replace it? Thanks for your input!

 

Dave

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If it is a 6V battery it has three 2.2V cells.  Charging it with 12V will just increase the charging amperage and generate excess heat.  If left alone it would eventually boil away the electrolyte.  Since you caught it early i don't think there was any damage done.  Are the plates still submerged in electrolyte?  If so, I'd keep using it.

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It's unlikely that a battery tender could supply enough current to damage the battery unless left long enough to boil the electrolyte out (as EmTee noted).  Their purpose is to replace self discharge losses to maintain the battery in a fully charged state and they can only supply a few amperes of current.  In addition, it's even more unlikely that a 1925 car had an actual voltage regulator...cars of that vintage depended on the battery itself to limit generator output voltage, and the maintainers I'm familiar with can't begin to supply as much current as the normal generator.\

 

Keith

 

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All good accurate advice so far. Just use the battery but check the water. The nominal charge for a 6 volt battery is 6.3v. It may be somewhat overcharged, or it may just have a bit of "surface charge". A little surface charge is pretty common in batteries in automotive use. Look at the water. If the plates are still covered it is extremely unlikely you did anything bad to it. Even if they are not, just put enough distilled water in to cover them up and try it. It isn't going to hurt your car. The worst thing it could do is work badly.

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Many thanks to all who replied. I appreciate the wisdom. Here’s the update: The electrolyte was indeed down, but just to the very top of the plates so I filled them with distilled water. I charged the battery (NOT with the tender-guess where it is!), and while I was down there cleaned the terminals and cable clamps. Hit the starter and the engine cranked fine! Now I can continue to try to figure out why it won’t start after having run fine a month previously. Again, thanks for the replies!

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You don't own a 12 volt vehicle?🤔 

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I am not familiar with the electrical system of a 1925 Maxwell, but no start conditions on these old cars are normally ignition or fuel related. I suppose your Maxwell has a vacuum tank fuel system, maybe with a electric fuel pump for lift, but essentially a gravity fed system. Saying the car was on a battery tender hints that it was not being driven regularly, and the fuel evaporates quickly in these old gas tanks. Check the carburetor float chamber and make sure there is gas there. If not, check your settling bowl, if one is installed, and if it has fuel, refill your vacuum tank with fresh gas.

Still no start. Well, a problem I have with my old cars, one is a positive ground 12 volt, one is a positive ground 6 volt, and one is a negative ground 6 volt, and the old tractor is a converted 6 volt positive ground, to a negative ground 12 volt, is leaving the ignition switch on and walking away from the car for a length of time. These old coils will overheat and fail if the ignition is left on and the ignition points are closed, and a cooked coil will result in a no start condition. Next, if it is a 6 volt system, and a 12 volt TRICKLE CHARGER, at 2 amps max were left on for a while, I would expect the circuit breaker of the charger to trip and turn it off……..but if it came back on as a charger, rather than a trickle charger, I doubt the battery would be hurt, but I’d closely check the wiring of my vehicle charging system to make sure it was still serviceable.

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Jack, thanks for your response. Rather than take this thread off topic, if you’re interested I would direct you to my original post in the Maxwell forum: 1925 Maxwell/Chrysler won’t start. I think it’s still on the first page. PM me if you want more info.

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22 hours ago, Frank DuVal said:

You don't own a 12 volt vehicle?🤔 

I do, but 1) they have their own tenders, and 2) when an electrical device made in an unnamed overseas country acts up, I tend not to trust it anymore.

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Many years ago I reversed the polarity of a six volt battery. The battery was completely dead in Spring and I thoughtlessly put a 10 Amp charger on wrong. The car started right up and ran fine but the ammeter went the wrong way, 1935 Nash. I asked a friend who is an electrical engineer and he said it was a long short but if anyone could do it I was the one.

 

I decided to make the battery dead, dead, again and charge it correctly. I clamped one of the firewall mount heat fans to the posts and sucked 'er down for a few day. It recovered and was in the car when I sold it.

 

Many people perceive a battery as a capacitor, thinking the charge process "fills" the battery with juice. It is actually the flow "though" the battery that converts electrical energy to chemical potential. Really surprising how common the misconception is. Well, that was the charitable way to comment.

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15 minutes ago, 60FlatTop said:

Well, that was the charitable way to comment.

Thanks for your charity!😁 I know enough about batteries and electricity to be dangerous. I thought it best to get some more knowledgeable input so in my ignorance I didn’t do any permanent damage. 

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