Is the Voltage Level Too High

I have a 1991 Miata and a one year old Westco Battery.

The Alternator has been replaced and everything appears to works fine, however, I checked for the Battery Voltage and it seems high.

(1) Voltage at Battery Treminals with MOTOR NOT Running is: 13.18 Volts.

(2) Voltage at Battery Treminals with MOTOR Running is: 14.58 Volts.

I called Westco Tech and they claim that 14.6 Volts, while engine is running, represents the High and is Acceptable.

I thought I'd ask Miata Group to see if there is any other opinion/ experience.

Also, if its too high, is there a way to adjuct the Voltage, from Alternator, DOWN?

Reply to
Pat
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The theoretical magic value is 13.8, but things like cold temperature will push that upward. 14.5 is on the high side, but not to worry about in my opinion. I had a van years ago that always ran over 15 volts. I replaced light bulbs unusually often, and I had to keep an eye on the battery water, but aside from that it wasn't a problem.

To my knowledge, the voltage is not adjustable, but I could be wrong.

Reply to
Dale Beckett

Both of those readings sound real good. Theoretical max for a fully charged "12 volt" battery is 2.25 volts per cell, or 13.5 volts total, and a "12 volt" alternator in good working order is almost always set to push its matching battery's theoretical max "plus half a cell" - Which would make your 14.58 volt reading just the slightest bit on the low side of "perfect".

Adjusting the output voltage on an alternator is at least theoretically possible. In the old days of mechanical voltage regulation, it was a simple matter of turning a screw or bending a tab on an external regulator module. These days, voltage regulation is almost always done inside the alternator by varying the current on the stator coils via a built-in semiconductor, so while it's not impossible, it usually isn't particularly practical.

Reply to
Don Bruder

It depends on the vehicle. Years back GM used to set output voltage to around 13.? (memory fails, sorry.), Ford to around 14.8V and Mopar in between the two. Since regulators are no longer adjustable it's difficult to find specs now but I doubt there's been any changes.

I wouldn't worry, it's reasonable.

Reply to
XS11E

There are all sorts of "funnies" when you get into what the charge voltage limit should be for an automotive lead acid battery. First, all automotive batteries are not created equal. As a result, the ideal charge voltage limit is a few tenths of a volt different between different batteries.

Next, more specific to the Miata-- When the battery is a fair distance from the regulator and alternator, there is some drop due to resistance in the battery cables that allows the charge voltage limit to be increased slightly.

Finally, smaller batteries need to charged to a higher level than a larger battery, so that more of the batteries capacity is available.

The there are "AGM" batteries that can be charged to a slightly higher voltage than the old lead acid battery, if the charge current is lowed to about 2 Amps.

There is more than you 'd ever want to know about batteries on the internet.

14-14.6 seems to be the most comm>
Reply to
Chuck

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