Can 14.4 V be too much of a good thing for 12 V battery?

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BuckMkII

Well-known member
Joined
May 6, 2017
Messages
258
Location
Seattle
I noticed when frequent rain began in the fall that LeafSpy showed the DC/DC converter maintains 14.4 V for as long as the wipers are on, and that my attempts to recharge the 12 V battery manually with an external charger every-other weekend resulted in the charge rate immediately dropping to near zero, indicating (if I'm not mistaken) that the battery was already fully charged.

So, great! When we had an unusually long period of no rain in December, I made a point of running the wipers on the lowest intermittent setting on about a third of my trips, just to keep the 12 V battery topped up. Now I'm just wondering: if it rains all the time, is there any risk of overcharging the 12 V battery by keeping the voltage high all the time?
 
BuckMkII said:
I noticed when frequent rain began in the fall that LeafSpy showed the DC/DC converter maintains 14.4 V for as long as the wipers are on, and that my attempts to recharge the 12 V battery manually with an external charger every-other weekend resulted in the charge rate immediately dropping to near zero, indicating (if I'm not mistaken) that the battery was already fully charged.

So, great! When we had an unusually long period of no rain in December, I made a point of running the wipers on the lowest intermittent setting on about a third of my trips, just to keep the 12 V battery topped up. Now I'm just wondering: if it rains all the time, is there any risk of overcharging the 12 V battery by keeping the voltage high all the time?

That's within the range that a normal ICE car alternator will put out all the time so I wouldn't think it particularly detrimental to the battery. You may have to add water more frequently if it's a maintenance type battery. "Float" voltage is lower but that's generally for keeping batteries topped up for periods of weeks, months or years.
 
LeftieBiker said:
The wiper motor will be taking enough extra juice from the battery to keep it from overcharging.
This statement is incorrect. The DC/DC converter can output about 1700 watts at all times,
which is well beyond what both battery, and wiper will draw, resulting in no voltage change,
thus no taking away of power.
 
cliff said:
LeftieBiker said:
The wiper motor will be taking enough extra juice from the battery to keep it from overcharging.
This statement is incorrect. The DC/DC converter can output about 1700 watts at all times,
which is well beyond what both battery, and wiper will draw, resulting in no voltage change,
thus no taking away of power.

Point taken. The car's charging system has to be relied upon to not cook the battery. Since it's more inclined to "starve" it, that isn't a problem.
 
I was pondering how hard it would be to add a "wiper defeat" rocker switch: you'd turn-on the wiper at the control stalk, and the car would think it's on (and boost the DC voltage to 14v); but the wiper would not actually be running. Then you'd use the rocker switch to actually turn the wiper on/off.

Even better would be to snoop the CANBUS, and find what system is sending a command to the DC/DC converter ("Yo! The wipers are on, increase output to 14v!"). Then clone that message, and inject it onto the bus at some random interval (e.g. once per hour in the READY mode).
If an average car trip lasts 20 minutes, then it would kick in about once per 3 trips, and you'd get an average of 10 minutes of 14v charging per 1 hour of driving. (call it "Seattle Mode").
 
specialgreen said:
I was pondering how hard it would be to add a "wiper defeat" rocker switch: you'd turn-on the wiper at the control stalk, and the car would think it's on (and boost the DC voltage to 14v); but the wiper would not actually be running. Then you'd use the rocker switch to actually turn the wiper on/off.

Even better would be to snoop the CANBUS, and find what system is sending a command to the DC/DC converter ("Yo! The wipers are on, increase output to 14v!"). Then clone that message, and inject it onto the bus at some random interval (e.g. once per hour in the READY mode).
If an average car trip lasts 20 minutes, then it would kick in about once per 3 trips, and you'd get an average of 10 minutes of 14v charging per 1 hour of driving. (call it "Seattle Mode").

Yes... "Seattle Mode"... I like that! Let me know if you make this happen.
 
I can only speculate that they set the voltage to 14.4 with wipers to achieve either:
- A certain wiper speed
-brighter headlamps during inclement weather. Incandescent bulb output is strongly influenced by voltage, and the LEAFs habitual under-volting is behind many of the "terrible high-beam" complaints with the incan bulbs, I believe.

Which begs the question of why they normally set the voltage lower. If I had to guess I'd say it is to minimize gassing of the 12V battery. This would have 2 advantages

- less maintenance required
- less of the acidic mist that is is often generated in ICE installations. This could be of particular concern with the amount of power electronics under the hood.

Of course that could be easily mitigated by use of no-maintenance battery and/or vent tubes. So it seems like a weak argument but that's all I got.
 
-brighter headlamps during inclement weather. Incandescent bulb output is strongly influenced by voltage, and the LEAFs habitual under-volting is behind many of the "terrible high-beam" complaints with the incan bulbs, I believe.

I had the same thought, but can detect no increase in headlight brightness when the wipers are on.
 
BuckMkII said:
I noticed when frequent rain began in the fall that LeafSpy showed the DC/DC converter maintains 14.4 V for as long as the wipers are on, and that my attempts to recharge the 12 V battery manually with an external charger every-other weekend resulted in the charge rate immediately dropping to near zero, indicating (if I'm not mistaken) that the battery was already fully charged.

So, great! When we had an unusually long period of no rain in December, I made a point of running the wipers on the lowest intermittent setting on about a third of my trips, just to keep the 12 V battery topped up. Now I'm just wondering: if it rains all the time, is there any risk of overcharging the 12 V battery by keeping the voltage high all the time?

You probably have not noticed that working voltage of ANY car is in the 13.5-14.5 volt neighborhood while the car is in use...

Anytime the car is running, the alternator is charging the battery at this voltage to cover for all of the accessories, a/c, heat that use up power. That way the 12v battery does not discharge.

Just because the system voltage is "higher" when the car is running, does not mean that the 12v battery is being over charged. Every 12v battery charger has a voltage in the 14 volt range..

Don't worry about it.... All this is normal. The time to worry is if the "running" system voltage while running starts going down to 12v volts or lower.... That means the car is not charging the battery.
 
smkettner said:
Higher voltage is ok when a bit chilly out so no harm when raining.

I notice this as well (14.4+V when colder)...and no, it doesn't hurt a thing. Even my LiFePO4 battery can accept that at the high-end of the range.
 
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