Proper alternator output to maintain battery?

[Ed_Flecko]

I'm doing a little preventive maintenance on my Toyota truck, and I'm curious about alternator output. Specifically, I'm wondering what is a "proper" alternator output to maintain the surface charge on my battery?

With the motor running and all electrical accessories turned on, "Eric the Car Guy" says that a battery voltage measurement of anything that's at least .5V higher than resting battery voltage is fine and means that the alternator is working fine. In his video (Time 5:20 - https://www.youtube.com/watch?v=FTGz0PKIl84), the alternator puts out 13.16V and he thinks that's great! However, Tony Candela of CE Auto Electric Supply (https://ceautoelectricsupply.com/) says it takes a MINIMUM of 13.4 Volts to keep a surface charge on a battery. Less than that will start to discharge your battery. Time 5:19 - https://www.youtube.com/watch?v=7yTyUw-Z5o4

Who's right?

Thank you,
Ed

 

[HerrStig]

13.5 is a standard figure but to get to that most alternators run 14.7 or so when the battery is down in charge and cold and taper down from there. If your truck is new enough the regulator function may be controlled by the ECU.

 

[SHOZ]

At 13.5 I'm thinking of getting the alternator fixed. My Hyundais which have ECU controlled alternators run at 14.3v until the battery is recharged from the start up then drop to 14.0v to 13.8v.

 

[BigD1]

If you you are into old Volvo 240's like I am, it's common to only be at round about 13 volts measured across the battery. Those are made in Germany Bosch alternators that run forever with brush changes. I changed a worn out set of brushes about 10 months ago, and I was getting 13.2 volts across the battery with the new brushes. Checked it a week later, and it was 13.1 volts which is normal.

 

[PeterPolyol]

14.7 for flooded lead acid batteries, no less than 14.4 for proper charging. Some cars have "smart" voltage schemes for fuel economy purposes that simply shorten battery life by bugging around with voltages; sometimes as low as 13 and as high as 15. These charging schemes may be fine for AGM batteries, but not flooded lead-acids. At least the mid-2000s GM alternator logic was woefully ill conceived and ruins batteries and leaves people stranded.

 

[Ed_Flecko]

So it sounds like you all think that "Eric" is wrong when he makes a blanket statement in that anything .5V or higher (when measured at the battery with the motor running) is adequate is actually too low?

Ed

 

[PeterPolyol]

Absolutely. 12.9-13.1 resting voltage puts that at 13.4-13.6 charging which may only achieve 80-85% SOC. Chronically holding a flooded lead-acid battery at that SOC is asking for sulphation and eventual failure to start in sub-zero conditions.

It's also noteworthy that "charging" voltage across terminals at idle may well be lower than the set regulator voltage as the hungry battery pulls amps trying to achieve full SOC. Regulator voltage can be accurately measured idling and battery disconnected.

 

[Ed_Flecko]

Originally Posted By: PeterPolyol
Regulator voltage can be accurately measured idling and battery disconnected.


I have heard that running a modern car with the battery leads disconnected is a RECIPE for disaster because your electrical system will start sending WAY too much power through the system...which will very likely blow the ECU.

???

Ed

 

[Leo99]

Preventive maintenance is good but don't be eager to fix things that are not broken. You suspect you might have a problem. I'd just keep an eye on it. Your alternator might have been at 13.16V for years before you ever measured it and everything was happy then or it might be starting to go. I don't think it will go suddenly but if that bothers you...You can put in a new one.

 

[PeterPolyol]

That's not impossible for extended periods of time with a lot of heavy load switching (and ripple), but not for briefly testing with no load switching. There is an adequate sum of capacitance on the system to reasonably protect from ripple. ECUs and other control devices are purpose built for durability with swinging voltage and ripple (and noise too). Modern control devices must endure 2-3 volt swings AT LEAST in normal operation. So unless it's a poor design or implementation, these devices are quite durable.

About charging, we should be careful about subscribing to generalized advice (ie Wiki) because conditions and battery usage determine what a proper absorption charge should be. In cars, these systems can be considered infrequent cycling and rarely (if ever) floating.

Floating charge voltage is a compromise between undesirable gassing and maintaining maximum SOC. Floating voltage does not often apply to the common automotive regime (unless the car runs 16+hours a day). Absorption charge is always higher than a maintained float charge and most solid-state (old style, 'unintelligent') regulators keep the voltage at just around an absorption charge voltage, which is ideal for FLA batteries in sporadic charging, infrequent cycling operation.

Here's a nice chart for your consideration

from this site

 

[SHOZ]

Originally Posted By: Ed_Flecko
Originally Posted By: PeterPolyol
Regulator voltage can be accurately measured idling and battery disconnected.


I have heard that running a modern car with the battery leads disconnected is a RECIPE for disaster because your electrical system will start sending WAY too much power through the system...which will very likely blow the ECU.

???

Ed
One of the way Hyundai says to test the alternator output is to disconnect it from the battery. If the voltage rises to the normal +14v things are good, if connected it drags the voltage down it's usually a bad battery.

 

[Johnny2Bad]

The alternator voltage must be higher than the battery stored voltage to charge the battery. Certainly there are ideal values here but the point is if the battery is at 13.2V and the alternator is putting out 13.3V, that is sufficient. It is worth mentioning that it is very possible to have too high a voltage and such high voltages can damage the battery, so "more" is not necessarily better. If you are reading perhaps 15.5V or higher, something may be amiss.

I believe the Toyota alternators utilize a voltage regulator that requires "flashing" to reach proper charge voltage. This means you must blip the throttle above a specific RPM to initiate charge output (usually around 1800 RPM). Once that is done, the alternator should charge when the RPM drops to at or near idle. Other alternator types will charge at idle but won't reach full charge output until some RPM off idle. I might be wrong about Toyota types but regardless, the take away is there are two types and you should determine which you have, or as a standard practice blip the throttle once to perhaps 2000 RPM upon startup and not worry which type you have.

The best test (and a simple test) for alternator function (and probably more important, Voltage Regulator function) is to park the vehicle near a wall or garage door, then turn on the lights at night, and increase the RPM from idle. If the lights are bright and solid in illumination then you are running off the alternator and the battery can be assumed to be charged or charging.

If the lights increase in brightness as RPM increases and dim as RPM falls, then the alternator is not putting out enough voltage to run the vehicle and you are using the battery for at least some of the electrical energy. In that case, further investigation may be warranted.

(Be sure to try the "blip the throttle" step outlined above, to insure the voltage regulator is active, if necessary).

I would caution against running a vehicle with the battery disconnected as this can damage some systems. Now, I myself have done so on occasion with my own vehicles but to be honest I don't recommend it to others.

I have great respect for Tony Candella but I also do not agree with every thing he says.

If you want to measure the alternator output you must put the Digital Voltage Meter (DVM) *between* the battery and the car's charging circuit. For example, disconnect the battery's ground lead, connect the DVM's + lead to the battery's - terminal, and connect the DVMs - lead to the vehicle ground. Now the DVM will read the voltage going through the system. Use alligator clips, do not hold test leads with your fingers. Things can get very hot and batteries store hundreds of amps of current.

Never do anything underhood or around the battery without wearing eye protection. I have seen a lead-acid battery explode in a vehicle. It WILL get in your eyes. Don't risk it.

 

[wrcsixeight]

The alternators output is decided by the vehicles voltage regulator which is either in the alternator or external to it and could be in the engine computer.

With a fully charged healthy enough battery, with a hot running engine, and Lights on high beam and blower motor and AC on highest speed, the voltage measured at the battery terminals would ideally be 13.7v or higher.

If it is below this, turn off the AC, and see if it climbs.

Many vehicles cannot produce enough amperage at hot Idle to produce enough amperage to cover all the DC loads turned on at once. but revving the engine to above 1200 rpm should allow the alternator to overcome all DC loads and increase battery voltage to at least 13.7 and preferable 14.4v.

My 50/120 amp alternator can do 54 amps when hot and 120 when cold and spinning at at least 2200 engine rpm. My loads can easily exceed 54 amps though, especially when battery is depleted.

Don;t assume the one time you cecked battery voltage is the voltage the vehicle will always show. Voltage will swing wildly when there are large loads involved and differing engine rpms.

Saying my alternator outputs 14.2v is like saying my morning coffee is always 98f from first sip to last.

 

[Ed_Flecko]

Great information...thank you all!



Ed

 

[SHOZ]

I have AGM batteries too in both cars. They tend to run a bit higher voltage than the normal FLA battery due to the specific gravity of the electrolyte being a bit higher. Normal FLA should be around 1.280 sp at 77F and the AGMs will be around 1.310 sp or so.

 

[Vikas]

If you are trying to get more life out of battery by putting the new alternator in, I am banging my head against the wall. Replacing battery is cheap and easy. Replacing the alternator is expensive and usually lot more work.

As long as alternator voltage is higher than the battery voltage, the power requirement of the car is being satisfied by the alternator. While the car is running, the power should be coming from the alternator.

 

[SHOZ]

If you want a longer life from a FLA battery you should get the biggest you can fit and reduce the acid's specific gravity to down around 1.230-1.240 or so.

 

[440Magnum]

Originally Posted By: Ed_Flecko
Originally Posted By: PeterPolyol
Regulator voltage can be accurately measured idling and battery disconnected.


I have heard that running a modern car with the battery leads disconnected is a RECIPE for disaster because your electrical system will start sending WAY too much power through the system...which will very likely blow the ECU.

???

Ed


Its not that it will "send too much power" through the system, but that the voltage becomes unstable. The voltage regualtor is a control system that assumes a certain amount of damping is provided by the battery. Without the battery the voltage spikes high, then shuts down, then spikes high... all very quickly. Not at all good for electronics.

 

[440Magnum]

Originally Posted By: Vikas
If you are trying to get more life out of battery by putting the new alternator in, I am banging my head against the wall. Replacing battery is cheap and easy. Replacing the alternator is expensive and usually lot more work.

As long as alternator voltage is higher than the battery voltage, the power requirement of the car is being satisfied by the alternator. While the car is running, the power should be coming from the alternator.


True, but the alternator has the secondary job of maintaining the charge of the battery. Car electrical systems are actually fairly terrible at that. To properly charge a battery, it should be done slowly and in stages. Beginning with a discharged battery, there should be a constant-current bulk charging phase, where the voltage slowly ramps up over time. Once that is complete, there should be an absorption phase where the current ramps down and the voltage is held constant over time (this is typically 13.5-13.8 volts for a flooded lead-acid battery). Finally, there should be a very low-current and higher voltage finishing charge at about 14.5 volts.

Car charging systems only approximate this, because there can be no assumption that the engine will be left running long enough to do the job. So they bang the voltage to the absorption phase voltage (often compensated for ambient temperature), and call it good. That results in a much faster than ideal bulk charging rate. And it also forgoes the finishing charge, which gradually sulphates the battery. Also, flooded batteries periodically need a time-limited, high-current, high-voltage "equalizing" charge where the voltage is pushed well above normal and the electrolyte boils. The individual cells tend to recharge at slightly different rates over time, and pushing a high current through all of them tends to equalize the state of charge as well as de-sulphate them. There's no way for a car to automatically do that, since it would push the system voltage high enough to pop headlamps and damage other components.

That's (plus the vibration and heat) is why car batteries don't last 10 or 20 years like the same type of battery in a more conrolled re-charge environment can. AGM batteries are much more tolerant of non-ideal recharging, never need the equalizing step, and hold up a lot better in automotive use IMO.

 

[brave sir robin]

Ranking of charging system sophistication with my vehicles and results.

1. Pathfinders Voltage is heavily influenced by battery charge level and under hood temps (volts drop as temp and or charge level increases). It ranges between 13.3 and 14.55 with battery resting at 12.6ish volts on a 1 year old battery.

2. Electra is externally regulated with a solid state upgrade. It does not compensate for temps or state of charge. Voltage at battery with engine running is 14.38 no matter what. Resting battery voltage is currently 12.57 on a 4 year old battery. I wish it had some type of compensation because I believe constant charging voltage is causing a bit of outgassing.

3. Aprilia is externally regulated but does not actually "regulate". instead it dumps excess current into heat and there is no type of load compensation. Voltages are 14.4 - 14.5. resting battery charge is around 12.78 on a two year old high end AGM battery.

All three of my vehicles have very robust charging systems with fresh up-sized cables and extra grounds etc.