What's a good frequency range for PWM of a truck alternator? Cummins 5.9 liter diesel engine on a Dodge Ram.
In the circuit I've designed, the frequency varies with duty cycle -- it hits its highest frequency at 50% duty cycle. Just looking for a ballpark range -- 100 to 1 kHz, 1kHz to 10 kHz, or what? I know 100 Hz is fast enough not to see headlight flicker, but might there be some other reason
100 Hz would be too low...?
A little background. I'm using PWM for a couple of reasons -- won't need a heat sink, and it's an interesting challenge. The stock configuration in this truck has the vehicle's computer doing linear control of the field, holding the system voltage at a measly 14.2 volts. This truck eats up a lot of electrical power in the winter what with the intake air heater and other stuff I have installed. Would have to drive for many hours between each start to get the battery back up to anything near a full charge, especially in cold weather. Batts (truck has two) are chronically a littlle low even in the summer. So I intend to up the voltage to about 15 this winter for the batteries' sake.
I'm not going to bother trying to find out if it's even possible to reset the voltage at the computer. Both ends of the field connect to terminals outside the alterntor, making it dead easy to install my own DIY external voltage regulator.
The usual problem is in driving the inductance, and that gets harder (obviously) as you aim for a higher frequency. There is a sound reason for quasi-DC drive. Far easier would be to fool the pootah's comparator. (add a diode mebbe?)
--
| James E.Thompson, CTO | mens |
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| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
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The Democrat theory is that spend.. spend.. spend.. and government
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You will find the regulated voltage will go up in colder weather, most automotive charging systems are temperature compensated. Interesting they control the alternator externally. My son once had a alternator cutout to increase acceleration by unloading the alternator!! I imagine Dodge is doing something similar, or had other reasons to use a little more smarts than common voltage regulator.
Cars typically run around with the batteries less than "full". It takes a long time to top up a battery, charging too hard can damage it. It would be best to use a trickle charger or maintainer. Be resourceful and make an inductive trickle charger you park over. No hassles about connecting it. It could have vehicle sensing, so it only ran then a vehicle was present.
At Idle, in drive, lights on, AC on, wipers on, brake lights on, On a warm summer night, you'll probably need full field voltage. So, forget about duty cycle.
14.2 volts is (good) normal, 15 volts will equalize the batteries and eventually destroy them. Does the voltage drop at idle from 14.2v with accessories on?
Your probably better off getting a heavy duty alternator. Most consumer alternators are output limited at idle. .
Most likely the computer is already using a pwm scheme to control the alternator.
Since you indicate that the cpu is controlling the field, we can only assume it also must regulate the voltage for the alternator ? I find that a little disturbing my self actually, unless this is a safety control system to shut down the alternator in the event of run away, which is more plausible ?
In any case, if the computer really is monitoring this voltage and regulating it, I don't think you'll do much with this since it's likely the monitor point is internal and changing the voltage will most likely alert the system of a alternator regulation failure and shut it down!.
You could try if you wish, to insert a diode in series to the CPU with a cap on the other side. If the voltage is truly being monitored internally to be regulated, this should force the ECM to pump it up another .6 volts of so. Or, there maybe a another input like being used for this which you can do the same thing.
In chrysler products, it is... (in virtually all alternators they use PWM...
The regulator is part of the ECM's job.
Reduced costs was teh reason, there were spare CPU cycles, the additional circutry was minimal.
I assumed that OP was going to remove the entire ECM circuit and drive the alternator directly (perhaps on a different platform?) He will have to consider the fact that the ECM will go nuts when it tries to regulate voltage and can't...
Well the ECM will set a code or two... Might go into a limp-home mode. Not sure it would shut the engine down, and since the OP is removing the ECM to alternator connection (again, an assumption) it can't shut the alternator down...
The real question is WHY does the OP want to do this? Is he using a Chrysler alternator on a different platform?
Before ECU's this was rarely the case. Thumb thru my patents.
[snip] ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
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| 1962 | I love to cook with wine. Sometimes I even put it in the food.
Generalizations! See my patents... voltage set-point is significantly a function of temperature.
Alternators often run at 6-7X engine RPM's. ...Jim Thompson
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| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I assume that the battery is providing a really large output filter.
The inductance of the field is quite high but isn't very good at high frequencies. This argues for using as low of a frequency as you can get away with. Making the alternator output current flow to the battery with about a 50% duty cycle would be ok.
The fact that the inductance has a poor Q, suggests to me that you may be better off if you had some inductance in the PWM circuit to prevent current surges at the switch on point.
ark
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I think I would go with not much more than 200Hz. Ideally, you would like the circuit to switch the field drive off quickly if the voltage goes too high and on quickly for too low. In the middle band, a 200Hz
50% duty sounds OK to me.
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Pushing the voltage up is not such a great idea. You need more charging current. Chances are the alternator is running near full blast already. You may need to put in a bigger one or a second one. One thing that is working for you is that a cold alternator will put out a lot more voltage that a hot one.
What would be very nice but not practical would be to spin the alternator faster at idle by having a gear shift in its drive. This way you would get full power from it at idle. They are designed so that they will charge the battery at idle but not at the full current.
ls
Beware that your computer may decide that the regulator / alternator function is not working right and turn on the check engine light.
"MooseFET" wrote in message news: snipped-for-privacy@y10g2000prg.googlegroups.com... On Oct 2, 2:15 pm, "Michael Robinson" wrote:
You have several options here.
I assume that the battery is providing a really large output filter.
The inductance of the field is quite high but isn't very good at high frequencies. This argues for using as low of a frequency as you can get away with. Making the alternator output current flow to the battery with about a 50% duty cycle would be ok.
The fact that the inductance has a poor Q, suggests to me that you may be better off if you had some inductance in the PWM circuit to prevent current surges at the switch on point.
I think I would go with not much more than 200Hz. Ideally, you would like the circuit to switch the field drive off quickly if the voltage goes too high and on quickly for too low. In the middle band, a 200Hz
50% duty sounds OK to me.
Pushing the voltage up is not such a great idea. You need more charging current. Chances are the alternator is running near full blast already. You may need to put in a bigger one or a second one. One thing that is working for you is that a cold alternator will put out a lot more voltage that a hot one.
What would be very nice but not practical would be to spin the alternator faster at idle by having a gear shift in its drive. This way you would get full power from it at idle. They are designed so that they will charge the battery at idle but not at the full current.
Beware that your computer may decide that the regulator / alternator function is not working right and turn on the check engine light.
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Yeah, I already hooked up my voltage regulator to the field, didn't disconnect or alter the stock wiring harness in any way. My reg is just running in parallel with the truck's regulation scheme. Nothing untoward happens but that the check engine light comes on, as you say, if I adjust my reg's voltage higher than the truck is set to. A couple of notes in answer to things others have mentioned. Adding a diode to fool the computer is kind of impractical. Where would I put it? You should get under the hood of my truck and start nosing around in the wiring harness, trying to figure out where to put a diode, before you issue armchair advice. Now hush up. Yes, I DO need to raise the voltage, and it's not a bad idea, especially since I have a pot on the board and can adjust it for condititions. I might even add temp sensing at some point. But here's why I need higher voltage: Before even starting the truck in winter, I have to run the air intake heater, which sucks up mega juice. Like starting current almost, but it lasts much, much longer. So I have drained a significant amount of power from the battery before even starting. Try driving a diesel like mine on short trips every day, without time to charge the battery back up. It will get weaker and weaker unless you do highway driving every day. I can already tell the difference from installing my v reg, the battery gets much better charging and turns over a lot better every time I start it. I keep it at 15 volts or a bit less, but if I'm going to be on the highway for hours at some time I can just dial it down a little bit so it doesn't overcharge. A lot of people mentioned temp sensing, but nobody mentioned that the charging voltage should vary with S.O.C. I can adjust for both now.
I usually go above the audio threshold but mind animals (thery hear very much higher than we do). I don't know alternators enough to say whether they'd like such direct PWM or whether current-sink switcher plus filter would be better. PWM in the audio range could cause a nasty buzz on the stereo.
15V might damage your battery.
If that's so easy to get to, where does the vehicle computer sense how high the battery voltage is? Not sure if this would be feasible here, but what if you'd place a (big enough, if it uses its own supply to gauge Vbat) P-Channel FET in series there? This you could be controlled via a circuit that makes your desired 800mV drop at this FET and the computer would now "think" that 15V is really 14.2V. Can be adjusted for outside conditions if desired. I still believe 15V can eat your battery.
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Regards, Joerg
http://www.analogconsultants.com/
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Use another domain or send PM.
An quick read of my ancient patents will show you how to easily temperature compensate a regulator.
Maybe it's time to again demonstrate my excellence in circuit design ?:-)
Do modern alternators use a low-side or a high-side switch on the field? ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
If I\'m talking, you should be taking notes.
Maybe on your failing American vehicles but not the German vehicles. = Even on your American cars I still doubt that there will be any changes = in voltage. Nowadays people use 2-pass voltage regulators, testing = under extreme and normal heat. There shouldn't be any change, = alternator chassis is connected directly to the engine chassis, same = temperature.
Don't assume! and don't spread false analysis like John Fools and his = gang.
Before my designs of the early '60's, the regulators were electromechanical, and high-side. Then we went low-side to accommodate readily available power NPN transistors.
Car companies will do weird things just to save the cost of a wire, so I'm not sure what's in use now. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
So would I. The epitome of frugality was my Citroen 2CV. Alternator on the crankshaft, no belt costs, meaning no belt to break. In fact the car did not have any belts. Not even safety belts but I put good ones in there. Distributor? Nope, too expensive, coil was across two spark plug tips so it always fired on both cylinders. That made for some "interesting" effects when starting via a hand crank, including the embarrassing moment when the 2nd muffler pot blew off the pipe with a loud bang and rolled down the street.
The gen was a DC brush type and AFAIR only one fat yellow wire went there. The regulator was a large metal pot with rheostats and huge relay contacts so they probably did it bang-bang. The whole gen was smaller than a coke can.
Oil pressure switch? Nope. Overtemp lamp? Nope. Other than a charge failure light there was nothing on the dashboard. Well, there wasn't really any dashboard.
[...]
--
Regards, Joerg
http://www.analogconsultants.com/
"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
An accident waiting for a location ?:-) ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Actually this car was known for totally resisting rollovers unless you hit some obstacle really hard. Once I heard a very loud bang but the car kept riding normally. Stopped at the RF institute, got out, car slowly leaned to the left. Took a look, the rear left was completely blown to shreds. The gas tank was in a bullet-protected setting between its double-I beams. Of course, if someone would be crashing a Dodge Ram into you, well ...
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Regards, Joerg
http://www.analogconsultants.com/
"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Back in 'the old days', electromechanical regulators were basically PWM implemented with a relay. These operated at the lower end of the audio range, with no adverse effects to the radios of the day. The battery makes an excellent low pass filter.
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Paul Hovnanian mailto:Paul@Hovnanian.com
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