Automotive electronics - Honda charging system

So roll your own regulator. I've previously posted the voltage required versus temperature. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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That voltage range should be fine if the battery is in good condition and y ou drive reasonable length trips. Charging systems today are designed to ma intain a battery but not necessarily do a full recharge which takes many ho urs. One exception might be driving several hundred miles. A sulfated batt ery is very difficult to charge because of higher internal resistance and s urface charge will build up quickly and reduce the charge current.

I assume you have a conventional flooded lead acid battery. It might be be st to put it on a good quality charger and see if you can restore the charg e. I would also check the specific gravity of each cell for any variation.

When my battery needed a jump, I found that driving 20 miles still left the specific gravity bordering on empty. I connected a Black & Decker 2 amp c harger/maintainer and the 2 amp charge terminated after about 20 hours but the specific gravity had only moved up a small amount. I left the charger/ maintainer connected for several weeks and to my surprise the specific grav ity slowly increased to 1.295 which is the upper limit. It was a very slow process all occurring as the battery maintainer float voltage rose from 13 .51 volts initially to 13.68 volts at the end of the period.

Make sure you measure battery voltage at the battery posts. In regards to your power supply reading 14.5 volts, there could be significant voltage dr op depending on wire size and length. Reading the voltage at the supply co uld show a higher voltage than what is actually seen at the battery posts. The state of charge would also be a factor and the voltage would be higher if the battery was close to full charge.

Yes, the no load voltage shows the state of charge. The trend is obvious - last fall it was 12.4V, a while ago it was 12.3V, now it is 12.2V. The battery will probably not last through the next winter.

The voltage drop in the car is negligible. The wiring diagram shows a 30A fuse between the 12V cigarette lighter and the battery. The voltmeter has a

100k resistor at the input. The drain is I = E / R, = 12 / 1e5, = 0.00012 A.

The wiring and fuse have very low resistance. Say we allow 0.1 volt drop at

30 A. The resistance is R = E / I, = 0.1 / 30, = 3.33 e-3 Ohms.

With the current drain from my voltmeter, the drop is E = I * R, = 0.00012

• 3.33 e-3, = 4e-7 V, = 400 nanovolts. The least significant digit on my voltmeter is 0.001 Volt. I cannot even see 400 nanovolts.

When chargin the battery, the power supply is connected to the battery with short lengths of 16Ga wire. The supply shows the voltage during current limiting. I never measured the voltage during this interval since it was so short. However, when it came out of current limit and the current decayed, the voltage quickly rose to 14.5V. So I take that as the voltage required to charge the battery.

It is clear the alternators in these discussions do not meet the minimum voltage required to charge the battery. At most, perhaps a few hundred mA flow, which will not restore the charge on a short trip.

I can't change the battery chemistry, or the length of the trips. But I can change the alternator output voltage. I am studying the schematics for the Ford Focus, and it seems the interface is very simple. It uses open- collector drivers for the command to the alternator and the feddback from the alternator. The frequency appears to be 150 Hz. It looks like all I have to do is cut the command line and insert my own signal, with the duty cycle selecting the desired alternator voltage. A very simple microprocessor can measure the battery voltage and change the duty cycle to drive the alternator voltage to 14.5V, and increase or decrease the voltage according to the ambient temperature.

I have high confidence this will work on the Ford Focus. I do not have schematics for the Honda, Camry, or other cars, so I cannot tell how difficult it would be to convert their systems to a controlled charging voltage. However, car manufacturing is driven by cost, and other manufacturers will probably use a very similar system.

It might be worth reconnecting your power supply to verify the charging thr eshold. If the wiring resistance was 0.05 ohms that would drop 0.25 volts at 5 amps. My battery at nearly full charge measured 14.24 volts with a 2 amp charge. The amateur radio site that I referenced earlier mentioned 14.

2-14.5 volts to charge in a reasonable time.

The Battery University website has information on the temperature compensat ion which is apparently 3 mv per cell per degree centigrade. That would be 0.18 volts for a six cell battery for a change of 10 degrees C or 18 degre es F.

I just realized that the alternator will warm up much faster than the heavy battery so the voltage may actually be too low until the battery warms up to compensate. That may never happen on a short trip.

Here is something else that might be of interest. There is a thread online mentioning that the internal resistance of a car battery is in the area of

0.02 ohms. That would drop the voltage 2 volts during a 100 amp load test. It would also mean that the charging voltage would need to rise an extra 0.2 volts under a 10 amp charge.

I actually calculated the same value earlier. My high beam headlights draw

10 amps. I turned on the headlights until the voltage stabilized and then t urned on the high beams. The additional voltage drop was about 0.2 volts. Using ohms law the series resistance would be 0.2/10 = 0.02 ohms.

My previous car was a 2000 Camry. A Sears Diehard battery installed in 2005 lasted 8 years which was quite a surprise. The battery still started the engine but the specific gravity of one cell indicated half charge. I now w ish I had measured the alternator voltage under different conditions. It's not hard to guess that the voltage regulator specifications differed from those of current models.

I think my battery was slowly discharged over time as a result of infrequen t use, short trips, and parasitic current drain. The surprise is that the b attery maintainer appears to have restored the battery to almost new condit ion.

The charging current drops rapidly as the battery is charged. At 50mA, the voltage drop is negligible. Say the resistance is 0.02 ohms. The voltage drop is then E = I * R = 50e-3 * 0.02 = 0.001 Volt, or 1 millivolt. That is the least significant digit on my voltmeter.

I think the problem is not so much measuring the battery voltage as much as convincing the alternator to ignore the commands from the PCM and set the charging voltage to 14.5V. Then the battery will be fully charged, even on short trips.

This voltage is mentioned in numerous places. But none of the cars deliver it.

It looks like fuel economy standards have really impacted voltage regulator specifications to reduce alternator load. I also would benefit if the cha rging system in my car was smart enough to properly charge the battery unde r all conditions.

I think 14.2 volts would still be adequate if it stayed at that level somew hat longer. The charge current should be a few amperes under those conditi ons and probably higher for a partially discharged battery. The voltage wo uld need to be under 14.2 volts at higher temperatures.

My thought on your power supply would be to adjust the voltage to 15 volts and let the current limit take over. In that case you should have a consta nt current 5 amp charge. The voltage at the battery posts would rise as th e battery charged but you could still measure the approximate threshold whe re the battery allowed a charge current of several amperes. The increase i n voltage should be very gradual as it can take a long time to fully charge a battery. If you did this starting from 12.2 volts, I believe the voltag e would rise fairly quickly as surface charge builds up on the plates. You could then see where the voltage leveled off before rising on a more gradua l basis.

I doubt fuel economy has much to do with it. Modern cars start so quickly that little energy is drawn from the battery. At 14.5V, the energy is replaced in a few minutes, then the battery drain drops to negligible level. Where you get the huge drain is heated seats, rear window defrost, high power audio systems, and all the various electronic gadgets that add to the alternator drain. Charging the battery is completely negligible, if the car manufacturers would settle on the correct voltage.

The battery accepts very little current at 14.2V. Many sites recommend

14.5V.

I did walk the current up at the beginning, but after a half-dozen or so times, I found it did exactly the same thing every time so I went to straight 14.5V and let it go into current limiting. The whole charge cycle only lasted a few minutes, then the battery drain rapidly dropped to 50mA or so and stayed there. The same thing would happen in a car.

Again, many sites recommend 14.5V to charge the battery.

Just for infomation, here is the lab power supply I used:

I bought three on the recommendation of another poster on this newsgroup. It turns out to be very poor for electronics work. There is a huge capacitor on the output. This will blow LEDs and ICs if you rely on current limiting to save the device. In addition, there is a large overshoot on power on, which could blow sensitive devices like laser diodes. I definitely do not recommend this unit for lab work, but it is OK for charging batteries. But I bought too many and paid too much.

I bought an Instek (Goodwill Industries) GPS1850D version for $17, but I prefer the 50 year old HP power supplies that I buy 'not working/for parts only' and rebuild. Some are so large that they need a decent relay rack to handle their weight. :)

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They don't get even. 

They go for over unity! ;-)

Not just gadgets, many cars have electric power steering, electric water pumps etc.

--sp

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Best regards,  
Spehro Pefhany

Thanks. I didn't know that. It sounds silly. To go from a pully on a power steering pump, to a pully on the alternator, then to an electric motor to drive the power steering pump or water pump, seems like a huge waste of energy. It has to affect gas mileage.

Thanks for the info. I did some research and found some good reasons for the switch to electric motors.

1. Power Steering

Electric power steering has some significant advantages over any form of conventional hydraulic steering, both for the owner of the car and its manufacturer. The reduction in engine load of an electric power steering system (it can be as low as 4 watts when the car is being driven in a straight line) means that the fuel economy of a car equipped with electric power steering is very similar to that of a car with no form of power steering. Analyses provided by manufacturers of electric power steering systems indicate potential fuel savings of 4-8 per cent over cars equipped with conventional hydraulic steering, with the lighter mass of an electric power steering also having an impact here. The independence of the system from engine operation also means that should the engine stall, steering assistance does not change.

110661

1. Not all agree it's better

Electrically assisted power steering (EPS) is the latest technological cross we bear. Replacing hydraulic assist with a computer-controlled electric motor seemed like a reasonable idea when it first surfaced.

in that direction. But in the past decade of driving EPS-equipped cars,

in comparison with the hydraulic-assist setups that have benefited from more than half a century of development.

1. Water Pump

According to Davies Craig, an electric water pump has a number of advantages over the engine-driven variety. They point out an EWP will increase power sent to the drive wheels because the power the mechanical

pump speed doubles from idle, say 600 rpm to 1,200 rpm, the power it takes increases by eight times, then eight times going to 2,400 rpm and so on. This extra power and torque released by disabling the mechanical pump now goes to the drive wheels. Additional benefits of an electric pump are improved cooling capacity and fuel economy along with the elimination of engine heat soak after a hot shut down. Engine cooling is improved with an EWP thanks to a higher flow rate at idle and low engine speeds when there is little or no ram air, and when the engine is switched off.

mp/

These arguments make good sense. Thanks.

On Saturday, July 15, 2017 at 5:09:06 PM UTC-7, snipped-for-privacy@gmail.com wrote: ...

less the point. The open-circuit alternator voltage will be nearly proporti onal to rotor speed till iron and copper loss take over. That's why I sugge sted a smaller alternator pulley (upthread someplace.)

The pulley size on car alternators is usually selected to give a maximum al ternator speed of abut 12,500 RPM at the maximum engine speed - beyond that speed the slip-ring contact, bearings and structural strength of the rotor etc start to have problems.

At that speed the open circuit voltage will probably be in the 100-150v ran ge - it is even possible to get 120V AC from a car alternator by modifying the regulator. At idle speed there should still be enough to provide power to the 12v system.

The output impedance of the alternator is highly inductive and since the im pedance rises proportional to frequency the current is somewhat independent of engine speed. Most alternators do not have any specific current limitin g - they just rely on this inductance.

kevin

Take a look at the first paragraph in this detailed description of the Hond a Dual-Mode Charging System. The CAFE standards have resulted in charging s ystems doing what they can to minimize alternator load.

to_pres

Yesterday I recharged my battery and wrote down some very interesting data. I feel much better about my voltage regulator settings at least for the in itial part of the charge. My battery was discharged enough for my 2 amp cha rger to run for 55 minutes. The battery started at a voltage of 12.75 volts and charged at 2 amps for the full 55 minutes. I checked the voltage at th e battery posts and watched the voltage rise all the way from 12.93 volts t o 14.26 volts. The rise was fairly steep initially taking 1 minute to reach 13.27 volts and 8 minutes to reach 14 volts. The rise then became more gra dual with the voltage rising to 14.26 volts after 55 minutes.

If an alternator had been doing the charging at a relatively constant volta ge, the charge current would have been quite high initially followed by a g radual decline. Consider the factors that determine charge current.

A simple model for a lead-acid battery would be a variable ideal voltage so urce in series with a variable series resistance. It's easy to see that ch arging current could be calculated using Ohm's Law. The three variables wo uld be alternator voltage, battery voltage, and the series resistance. Cur rent will flow whenever the alternator voltage is just slightly higher than the battery voltage which may include surface charge.

The remaining issue is what happens after surface charge builds up. It is p robably not a problem if the battery is near full charge. However, if a bat tery is at 50% charge, it takes time and amperage to restore the charge. Th e voltage regulator settings might be more important for this case to achie ve the required charging current. Short trips would be an additional conce rn.

You still never made it to 14.5V

It looks like you need to put your battery on charge after every trip.

You never made it to 14.5V

LTspice uses a large capacitor as a model for a battery.

You may need to put your battery on charge after every trip.

Nice answers. I think another factor is that the accessories can run for brief periods from the battery so more of the HP from the engine is available to drive the wheels when passing or going up a steep hill, thus allowing a smaller displacement IC engine to give the same performance as a larger one (which also reduces fuel consumption).

The servo steering can easily be made speed sensitive, which improves the driving experience.

--sp

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Best regards,  
Spehro Pefhany

Den onsdag den 19. juli 2017 kl. 00.48.22 UTC+2 skrev Spehro Pefhany:

and you get much more freedom on where you can place the various accessories

I really like the idea of not losing power steering if the engine quits. If you have ever lost the engine in a high speed curve on the side of a mountain, you may agree there is probably little that is so frightening.

My Honda keeps the alternator at 14.4V so long as the headlights are on. That shouldn't be necessary, but seems to work.