Automotive electronics - Honda charging system

On Wednesday, July 5, 2017 at 1:49:29 PM UTC-7, Peabody wrote: 

> I've never had a good feel for how long it actually takes to
> recharge fully after one engine start if the alternator is
> at max.  My Civic starts very easily, so I wonder if it
> needs more than maybe 15 minutes to recoup.  Could even be
> less I guess.

I've seen several threads discussing the time to recharge a battery after starting and estimates range from 2-30 minutes.

One method is to first estimate the cranking time and amperage.  Assume that you crank the starter for two seconds at an average current of 250 amps which represents 500 amp-seconds.  The charge current is hard to estimate but might be in the range of 5-30 amps.

If we use an average charge current of 5 amps, we could replace the 500 amp-seconds discharged from the battery in 100 seconds if no energy is lost.  The efficiency of a lead acid battery is considered to be 50-90% with the lowest efficiency seen near full charge. If we assume 50% efficiency, the recharge would take 200 seconds or a little over 3 minutes.

It sounds as though the Honda Dual-Mode Charging System is not keeping the battery fully charged. It's possible that the battery stays in a range where the state of charge is perhaps 60-70%. In that case, the battery is probably never recharged to 100% of capacity.

There are probably many other factors involved. Here is an excellent article that discusses surface charge in a lead acid battery that is worth reading.

http://www.smartgauge.co.uk/surf_chg.html

"The first thing to remember is that the process of storing energy in a battery is a chemical reaction. The idea is to turn as much as possible of the lead sulphate (which form the plates of a flat battery) into lead and lead dioxide (which form the plates of a fully charged battery). But this chemical reaction is actually quite slow."

"Initially the chemical reaction only takes place on the surface of the plates, where they are in contact with the electrolyte. It takes some time for this chemical reaction to start to penetrate deep into the plates. This is effectively the "surface charge"."

"It can mean that a very low charge current is going into the batteries because the surfaces of the plates are fully charged. But wait some time, and the surface of the plates will become slightly discharged. In effect they have discharged into the "deeper innards" of the plates. This is effectively what limits the speed at which lead acid batteries can be charged."

kt77 <kawill70@gmail.com> wrote:

> It sounds as though the Honda Dual-Mode Charging System is not keeping
> the battery fully charged. It's possible that the battery stays in a
> range where the state of charge is perhaps 60-70%. In that case, the
> battery is probably never recharged to 100% of capacity. 
 
> There are probably many other factors involved. Here is an excellent
> article that discusses surface charge in a lead acid battery that is
> worth reading. 
 
> http://www.smartgauge.co.uk/surf_chg.html

Thank you for the excellent and very interesting posts on this topic. I 
also have a chronic problem with keeping the battery charged on short 
trips. I use a Scangauge to monitor the battery voltage and compare it to 
a 5-digit voltmeter plugged into the 12 volt accessory socket. The 
Scangauge reads about 0.1 volt low.

I had a 2001 Ford Taurus that insisted on keeping the alternator output 
at 13.5 to 14.0 volts. This failed to keep the battery charged and it 
would sulphate. After losing three batteries in three years ($450 total), 
I decided to remove the battery after each trip, bring it inside and hook 
it up to a lab supply that current limited at 5 Amp.

Obviously the battery was charged a bit on the trip home, but as I raised 
the voltage, very little current would flow until I reached almost 14.5 
volts. Then the supply would rapidly current limit at 5 Amp. All this 
happened within about 0.1 to 0.2 volts. The current rise was very steep.

It only took a few minutes for the current to taper off down to 0.05 Amp 
where it would stay until the next time I needed the car.

My next car is a 2003 Ford Focus. I had to install a new battery shortly 
after purchasing the car. It has been happier with short trips but it has 
a very strange algorithm to charge the battery. In the winter when the 
temperatures are around -20C, the alternator voltage ranges from 14.5 to 
15.0 volts. In the summer, it ranges from 14.0 to 14.5 volts. I haven't 
taken the battery out and put it in the charger, but so far the car 
starts in 1 or 2 seconds summer or winter. Even on the coldest days there 
is no indication the battery is low. However, when I measure the voltage 
using the accessory output after the car has sit idle, the no load 
voltage measures 12.1 volt in the winter and 12.3 volts in the summer. 

I have turned off all loads such as interior lights, and I have added a 
separate relay that disables the door locks when I insert the ignition 
key. This draws 50 mA and I can see the battery voltage decreasing 
slowly, but it stops when I remove the key. So I know my low voltage 
readings are the open circuit battery voltage and not caused by an 
external load.

If you look at the various battery sites, these voltages indicate the 
battery has very little charge and should be sulphating. But it seems to 
work fine, so I'll leave it alone and keep monitoring the situation.

Thanks for the interesting information. I'll continue watching for your 
posts so see if I can find any information that could explain these 
strange readings.

kt77 says...

 > It sounds as though the Honda Dual-Mode Charging System
 > is not keeping the battery fully charged. It's possible
 > that the battery stays in a range where the state of
 > charge is perhaps 60-70%. In that case, the battery is
 > probably never recharged to 100% of capacity.

That appears to be the case.  And I think that's a charge
level that would never give problems in terms of being
able to start the engine.  In my case, it maintained the
battery at about 12.2V (measured in the morning after
resting overnight), which I think is about a 50% charge, and
I never had a problem starting - until the battery actually
died, which happened at under three years.  So while the
Honda system may give them great mileage numbers, and work
ok for starting, the lower average charge level results in
increased sulfation that significantly reduces battery life.

Last week I took my Civic into the dealer and had a
heart-to-heart talk with the service manager about a
technical sevice bulletin that I was never advised about.
It provides for flashing new charging parameters into the
computer.  They agreed to apply the TSB at no charge to me,
and since then, the alternator has spent most of the time at
14.4V.  But more important, when I measure battery voltage
in the morning, it's around 12.52V, which I think is
probably ok.  Not 100% charged, but I think close enough.

I think a better approach, which may be in effect on newer
models, is to allow the computer to completely disconnect
the battery from the charging system after the car has been
started and the battery brought back up to a full charge.
Then you could run the alternator at 12.0V, or even less,
but the battery wouldn't see that.  That would be very
efficient, but leave the battery fully charged, which is
what you want.

Or even better, there's the new alternative car battery
that's made up of lithium batteries, supercapacitors to
provide the cranking amps, and electronics to charge the
capacitors.  I don't know if it's ready for prime time, but
looks interesting, and, you know, the kind of thing we
should be able to do now, with all the environmental and
weight benefits.

https://www.youtube.com/watch?v=BsP0QGX1Qiw

http://www.getohm.com/

On Wednesday, July 12, 2017 at 2:32:57 PM UTC-7, Peabody wrote:

> They agreed to apply the TSB at no charge to me,
> and since then, the alternator has spent most of the time at
> 14.4V.  But more important, when I measure battery voltage
> in the morning, it's around 12.52V, which I think is
> probably ok.  Not 100% charged, but I think close enough.

The alternator voltage at 14.4 volts should make a big difference. I just found some information stating that you need 14.2-14.5 volts for a car battery to accept a reasonable charge current in amperes. That fits in with the information just provided by Steve.

I drove fifteen miles today watching my new INNOVA 3721 Voltage Monitor.  The voltage started out just below 14.2 volts and stayed above 14.0 volts for the next ten minutes.  As the engine warmed up, the alternator voltage dropped but stayed in the range of 13.5 volts to 13.95 volts.

I'll check the battery voltage in the morning to see how things look.  As a reference point, my battery charger/maintainer brought the battery up to the point where it read 12.82 volts after the surface charge had dissipated.

If you would like to confirm your state of charge, you could check the specific gravity assuming your battery has removable caps.  I'm using a hydrometer that is at least 50 years old.  My battery was slowly restored by the charger/maintainer and the specific gravity leveled off at 1.295 which is quite high.  Remember that sulfuric acid is dangerous and eye protection should be used.

Over the last week I captured some data that should be useful when my car is not driven for a week or more.  The battery voltage drifted down from 12.82 volts at a rate of about 0.015 volts per day.  If that rate is maintained, the battery voltage would only drop to 12.5 volts after 20 days.

It does appear that my car is quite light in terms of charging. A battery will charge at 13.8 volts but a full charge would take a long time.  I think the recharge time estimate for my car should assume a charge current that is only a fraction of an ampere.

> 
> I think a better approach, which may be in effect on newer
> models, is to allow the computer to completely disconnect
> the battery from the charging system 


No, technically the better approach is to charge the battery in the optimal way for battery life and not worry about saving a few drops of fuel.

But the car is now designed by politicians rather than engineers.
m

Here is a new data point that might be of interest. Yesterday I reconnected my Black & Decker 2 amp battery charger/maintainer to top off the battery. I happened to notice that the voltage under charge read 14.24 volts which is actually a very significant number.

Charging at a current above a few amperes can only take place at 14.2 volts and higher which is consistent with my reading. It also suggests that my charge current while driving will be very limited with the alternator output in the range of 13.5 volts to 14.18 volts. The only exception might be after starting the engine when there is no surface charge on the battery plates. The voltage differential between alternator and battery would be higher for a period of time and I would expect the charge current to be higher and then decline as surface charge builds up.

It looks as though my drive on Wednesday did an acceptable job charging the battery with the voltage at 12.85 volts the following morning.  The Black & Decker charger/maintainer charges to a somewhat higher level. I measured 12.88 volts this afternoon which was 22 hours after disconnecting the charger.

I'll also pass along a link to an amateur radio website with a lot of useful information. See the quoted text below which should be taken in the context of the 1970s.

https://www.w8ji.com/battery_and_charging_system.htm

"Since a 12 volt battery has six cells, any 12 volt lead-acid battery needs at least 13.8 volts to start to charge. This voltage will be enough to fully charge or maintain the battery on a trickle charge, but charging time will be very long at 13.8 volts."

"To fully charge in reasonable times, alternator output must be 14.2 V to 14.5 V as measured right across the battery posts."

"Less than 14.3 would be a "weak" alternator or regulator."

"When running at a normal slow cruising engine RPM, the voltage across the battery terminals should stay over 14.3 volts even with full load."

kt77 <kawill70@gmail.com> wrote:

> Charging at a current above a few amperes can only take place at 14.2
> volts and higher which is consistent with my reading. It also suggests
> that my charge current while driving will be very limited with the
> alternator output in the range of 13.5 volts to 14.18 volts. The only
> exception might be after starting the engine when there is no surface
> charge on the battery plates. The voltage differential between
> alternator and battery would be higher for a period of time and I
> would expect the charge current to be higher and then decline as
> surface charge builds up. 
> 
> It looks as though my drive on Wednesday did an acceptable job
> charging the battery with the voltage at 12.85 volts the following
> morning. 

Thanks for the new information and the link. It seems your infomation is 
very consistent about charging voltages. However, from your previous 
post:

"I drove fifteen miles today watching my new INNOVA 3721 Voltage Monitor.  
The voltage started out just below 14.2 volts and stayed above 14.0 volts 
for the next ten minutes.  As the engine warmed up, the alternator 
voltage dropped but stayed in the range of 13.5 volts to 13.95 volts."

This is similar to the readings I got on my Taurus alternator. However, 
this killed the battery in less than a year. I went through three 
batteries before I finally decided that Ford had no clue about charging 
lead-acid batteries.

In your case, you measured 12.85 volts after your drive. I don't see how 
that can happen with only 13.5 volts to 13.95 volts from the alternator. 
That is what killed my batteries.

More mysteries to unravel...

 

On Friday, July 14, 2017 at 3:48:46 PM UTC-7, Steve Wilson wrote:
>
> In your case, you measured 12.85 volts after your drive. I don't see how 
> that can happen with only 13.5 volts to 13.95 volts from the alternator. 
>
I also was surprised at the charge level the day after driving the car. The battery which is quite new had been fully charged with the battery maintainer. The engine starts in less than a second and the voltage rises to 14.18 volts after a cold start. The charge current could average 1 ampere over the next 5-7 minutes which could restore the charge. However, I also had two warm starts on that trip and the voltage stays under 14 volts.  A battery will still charge above 13.6 volts but at very low current.  It may be that the trip was long enough to restore the charge lost in starting.  There may be one other factor and that is the loss of surface charge when starting.  The lower battery voltage at that time might initially allow a reasonable charge current to flow while at 13.8-13.9 volts.  The key may be the differential between alternator voltage and open circuit battery voltage.

You mentioned something interesting when describing your power supply charger with current limiting. If I understood correctly, the current declined after a certain point and then leveled off at 50 ma.  I think that suggests that if you wanted to maintain a given charge current, you would have to slowly increase the charge voltage as the battery charges.

It's possible you could benefit from the use of a Solar Battery Charger. Several are available on Amazon and they can operate on the dashboard or in a window.  If you park outside in the sun it might be worth reading the reviews to see what you can learn.

kt77 <kawill70@gmail.com> wrote:

> On Friday, July 14, 2017 at 3:48:46 PM UTC-7, Steve Wilson wrote:
>>
>> In your case, you measured 12.85 volts after your drive. I don't see
>> how 
>  
>> that can happen with only 13.5 volts to 13.95 volts from the
>> alternator. 
>  
>>
> I also was surprised at the charge level the day after driving the
> car. The battery which is quite new had been fully charged with the
> battery maintainer. The engine starts in less than a second and the
> voltage rises to 14.18 volts after a cold start. The charge current
> could average 1 ampere over the next 5-7 minutes which could restore
> the charge. However, I also had two warm starts on that trip and the
> voltage stays under 14 volts.  A battery will still charge above 13.6
> volts but at very low current.  It may be that the trip was long
> enough to restore the charge lost in starting.  There may be one other
> factor and that is the loss of surface charge when starting.  The
> lower battery voltage at that time might initially allow a reasonable
> charge current to flow while at 13.8-13.9 volts.  The key may be the
> differential between alternator voltage and open circuit battery
> voltage. 
 
> You mentioned something interesting when describing your power supply
> charger with current limiting. If I understood correctly, the current
> declined after a certain point and then leveled off at 50 ma.  I think
> that suggests that if you wanted to maintain a given charge current,
> you would have to slowly increase the charge voltage as the battery
> charges. 
 
> It's possible you could benefit from the use of a Solar Battery
> Charger. Several are available on Amazon and they can operate on the
> dashboard or in a window.  If you park outside in the sun it might be
> worth reading the reviews to see what you can learn. 

As I brought up the voltage, the current rose from a very low level, 
perhaps 100mA, then suddenly went into current limiting around 14.5 
Volts. It stayed in current limit for only a few minutes, then gradually 
tapered off in a linear fashion down to 50 mA. Ther threshold is very 
sharp, perhaps 100 to 200mV.

This tells me the alternator voltage must be high enough to rise above 
the battery threshold in order to charge the battery. A lower voltage, 
even a couple of tenths of a volt, will do little to charge the battery.

Of course, the voltage changes with temperature. This is documented on a 
number of sites, but I believe the change is around -2mV per degree F. So 
on a hot day, + 30C, the threshold voltage will decrease, and on a cold 
day, -20C, the required voltage will increase.

The car makers have wildly differing opinions on what the optimum voltage 
should be. My neighour had a Pontiac Trans AM (I forget what year, 
perhaps around 2006), and her alternator put out 15.5V after starting. 

Definitely on the high side, but it didn't seem to harm the battery. The 
battery was a GM side mount and the connection got corroded, so I was out 
in -30C weather more than once to try and start her car. Fortunately, she 
traded it in on a new Nissan and I have not been asked to start her car 
since. Horay!

I got the bug to install a solar charger. There are a number of problems. 
For example, the sun angle in winter is very low, so the solar array has 
to be tilted to get much energy. However, the snow fall overnight can be 
half a foot or more, which would cover the array. Trying to brush it off 
might mean damaging the array, since it is hard to find under the snow. I 
did order three arrays to try to capture as much energy as possible, but 
only one arrived. The others were lost in shipment.

The other problem is trying to capture as much energy as possible, then 
to transfer it to the battery. One approach is to charge a battery bank, 
then start a SEPIC converter to charge the battery until the capacitor 
bank decayed to some suitable voltage. I found that the local electronics 
recycle bin often contains discarded high power stereo amplifiers, which 
contain large value electrolytic capacitors. I had collected quite a few
of these before I traded the old Taurus for a new Ford Focus. The Focus 
seems to be doing a bit better to charge the battery - a least it hasn't 
failed to start even in winter. So I am monitoring the situation and as 
long as the car continues to start, I see little reason to get excited.

However, now that the temperatures are starting to climb, I am getting a 
little nervous. The alternator is starting to put out 14.2 to 14.3V, 
which I believe is too low to charge the battery. Accordingly, the 
unloaded battery voltage is starting to decrease. It was 12.2v this 
morning. So I believe the battery is heading to an early death, which 
could be prevented if the alternator put out a higher voltage.

Now I am looking at making a simple circuit to intercept the PWM commands 
from the engine control, and inserting my own PWM command to the 
alternator to tell it to keep the voltage at 14.5, regardless of 
different loads such as air conditioning, headlights, and so on. Once the 
battery has charged, the drain on the alternator drops to insignificant 
levels, so the higher voltage should have little effect on the 
alternator.

I remember the old days when cars used a generator with brushes, and the 
regulator was some relays that you could adjust the voltage to whatever 
you wished. The battery would last for 5 or 6 years with no problem, even 
with the harsh winter. Now, the electronics have taken over, the the 
algorithms don't seem to have been written by someone who understands 
what they are doing. So I am interested in overriding their poor 
performance. But it is very hard to find any information on the PWM 
signals and how to insert a different command without upsetting the 
engine control software.

Sorry for the long post. There was a lot of detail to cover.

>As I brought up the voltage, the current rose from a very low level, 
>perhaps 100mA, then suddenly went into current limiting around 14.5 
>Volts. It stayed in current limit for only a few minutes, then gradually 
>tapered off in a linear fashion down to 50 mA. Their threshold is very 
>sharp, perhaps 100 to 200mV. 

>This tells me the alternator voltage must be high enough to rise above 
>the battery threshold in order to charge the battery. A lower voltage, 
>even a couple of tenths of a volt, will do little to charge the battery

IOW large lead-acid batteries have very low impedances, which is more or less the point. The open-circuit alternator voltage will be nearly proportional to rotor speed till iron and copper loss take over. That's why I suggested a smaller alternator pulley (upthread someplace.)

Cheers

Phil Hobbs