vintage car battery charge controller

[Thunderchild]

A friend has challenged me to build a charge regulator for his vintage car as apparantly the old dynamos are rather eratic and totally out of control and do tend to ruin the battery as they will just charge it till it cooks over 16 V even

My 2 main concerns for this project are:

1. what sort of current do i need to consider handling on this I would assume no more than 50-60 A so what sort of safety margin am I going for ?

2. what sort of thikness wire will I be using ? 10 sqr mm ? this will also determin to some extent the actual control tansistor used as I guess huge ring tags will be the order of the day on this.

My general plan is to PWM charge the battery to obtain some control over the eratic voltage, he suggested using a transistor to short out part of the coil (apparantly this is normally done manually for crude regulation) but then he is a mechanic not an electronics designer and i think PWM will be smoother and better. the only other issue there of course is radio interfearance.

 

[Mr RB]

Cool project. What voltage is it? 6v battery or is it a 12v conversion?

I don't think it will be as many amps as you think, the old cars didn't have the high power headlights and stuff that we use these days.

I would find out the voltage and the expected load, ie how many lights does he have and what wattage are they? You can probably buy a aftermarket Harley regulator for a generator which will do the job, since the regulator simply controls the field winding the same 15-20 amp Harley regulator should control a slightly larger (30 amp?) car generator with no problem.

Have a look here;
J&P Cycles® - Vintage Catalog

 

[Thunderchild]

I beleive 12 volts

I'm not really that concerned about the headlights etc because the generator (dynamo) will make what it makes and thats that, I'm interested in regulationg the output to preserve the battery, he may want to fix this device to all of his cars and possibly some of the ones he works on

 

[Externet]

Hi.
The key is to sense the battery voltage to not exceed 14.0V to feedback your pwm or other method you choose. An antique voltage regulator for field should be capable of working right if properly wired.
Or, build a LM319 voltage regulator set to 14.0 V driving a few bypass power transistors on heat sinks capable to achieve about 150% of all accessories current draw.
There is other preferable variable voltage regulators ICs with shutdown pin.

 

[MikeMl]

You need to understand how the generator is controlled. Read these attachments from my 1955 edition Motors Manual. If you need more info, I can scan the relevant section for you. You need to find out what type of generator your friends car has?

I deal with this because there a lot of 1950s/1960s aircraft still flying with generators. You can buy a ready-made solid-state generator controller which replaces the erratic and unreliable vibrating-point OEM regulator for about $100.

 

[tcmtech]

I made a number of homemade refits of those old buzzer regulators using a simple op amp voltage comparator circuit and a large transistor for the field control many years ago. They fit inside the original regulator housing and always worked well. I still have my original one from about 20 years ago and its still in service!
It just basically a slightly modified version of a stock external regulator the older Ford alternator systems use.

I used them on our old farm tractors until I got around to electrical system upgrades and installed high output alternators in order to keep up with modern lighting loads that were added then.

 

[user_88]

I beleive 12 volts

You need to check the system voltage. Some of the DC generators were made for 6 volts.

 

[tcmtech]

And if its a positive ground or a negative ground system!

 

[Thunderchild]

I made a number of homemade refits of those old buzzer regulators using a simple op amp voltage comparator circuit and a large transistor for the field control many years ago.

I assume you mean a comparatr circuit driving a power transistor which switched on and off basically creating a PWM output ? I did think of this too but I think as this is a purpose design I'll need to be prepared for all the bells and wistles I may get asked to put on so a pic (probably 12F615 I'm currently working with) will do the job, set it up to rum PWM and increase or decrease the buty cycle according to the battery voltage

 

[MikeMl]

...set it up to rum PWM and increase or decrease the buty cycle according to the battery voltage

You are forgetting an essential function of the OEM regulator, which is the over-current cut-out relay. The original regulators had at least two regulating relays, one which controlled output voltage (to regulate the voltage appropriate for keeping the battery maintained), and the other (to prevent burning up the commutator in the generator if the maximum rated current is exceeded).

 

[Thunderchild]

yes I guess an amperage cutout would be good too, I suppose the best way being a small series resistor I can sense the voltage on, where can I get such a small resistor ? so as to not create a large voltage drop and power dissipation.

 

[Thunderchild]

Mike, thank you very much for those copies they are quite informative, sounds like some sort of PWM was used by the oem regs too but using relays.

I'd be very interested to know more about the generator itself, at the end of the day I have to deal with the generator and the battery, I'm aware of how the battery works, I don't know a lot about pre war generators

 

[MikeMl]

...
I'd be very interested to know more about the generator itself, at the end of the day I have to deal with the generator ...

Yes, you need to determine what type of generator the antique car actually has in it. I have info about gennys that would have been in old US cars, but if the car is British, I probably cant help...

 

[Thunderchild]

well I'm interested in the principles more than the technical specs, why is there 2 outputs ? from my friends quike explanation i gather that say we have the negative brush, and the positive is 180 degrees in relation to it, is the 3rd terminal a third brush which is movable to vary the voltage ? see if I'm using electronic control i no longer need the 3rd terminal as I'll regulate the full voltage.

but taking into account the absurd, if the generator sudenly decides to output 18 v am i still safe putting thi into the battery albeit PWM ? I's say that would be about a 70 % output ?

 

[MikeMl]

The third brush is an INPUT (field terminal) to the generator. The generator's output is proportional to the average field current. You can control the generator's output current (~30A) by PWMing a much smaller (~5A) field current. You do NOT just put a PWM switch between the generator output and the battery positive terminal.

 

[tcmtech]

On the old farm tractors and American made vehicles there were two lugs on the generator body. One is the main power output from the armature and the second one is the field coil.
They are either set up in a field to case or a field to armature configuration. That is in the field to case set up if you connect the field and armature lugs together to get its full output (power to field lug). In the other design you tie the field lug to the case to get the full output (ground field lug).

One other problem is that back then they did not have diodes so they used a voltage sensing relay that would connect the armature to the battery if the armature voltage was high enough and then disconnect it when it dropped below a specific voltage That way the battery would not feed back to the generator if its output voltage was to low.
On the few solid state ones I built I just used a 20 amp dual diode type rectifier in a TO-247 case to replace the relay. Given that the old tractors I was working with only had about 15 -20 amps peak output just using the metal case of the old regulator for a heat sink was good enough.

I am not sure if current regulation is absolutely necessary. Many of the American made mechanical regulators didn't have it built into them. If the regulator is a square one it typically only has the isolation relay and the voltage regulator relay. Some had a current bias winding over the voltage control relay and used a sort of weak current bias to drop the output voltage if a high enough current was being drawn. The longer rectangular ones are typically the type with the adjustable current limiting built in.
Although many old charging systems didn't even have actual voltage regulators. Rather they just had the isolation relay and a specific value resistor inside the regulator box that just kept the generator at a proportional current output . The faster the generator turned the more amps it delivered. It was crude but still millions of them were used.

You are in fact right that they used a rather crude mechanical PWM of sorts. Thats probably why a basic comparator design works rather well. It uses the same basic effect as the mechanical system but is much faster and more accurate plus uses actual diodes and provids far better spike suppression than the buzzing contact regulation systems ever had.

Just some things to think about.

 

[Thunderchild]

ok I think I start to get it, so is this a generator with a stator coil and a rotor coil, the third terminal is to magnetise one (in place of permanent magnets)

 

[Thunderchild]

On the old farm tractors and American made vehicles there were two lugs on the generator body. One is the main power output from the armature and the second one is the field coil.
They are either set up in a field to case or a field to armature configuration. That is in the field to case set up if you connect the field and armature lugs together to get its full output (power to field lug). In the other design you tie the field lug to the case to get the full output (ground field lug).

One other problem is that back then they did not have diodes so they used a voltage sensing relay that would connect the armature to the battery if the armature voltage was high enough and then disconnect it when it dropped below a specific voltage That way the battery would not feed back to the generator if its output voltage was to low.
On the few solid state ones I built I just used a 20 amp dual diode type rectifier in a TO-247 case to replace the relay. Given that the old tractors I was working with only had about 15 -20 amps peak output just using the metal case of the old regulator for a heat sink was good enough.

I am not sure if current regulation is absolutely necessary. Many of the American made mechanical regulators didn't have it built into them. If the regulator is a square one it typically only has the isolation relay and the voltage regulator relay. Some had a current bias winding over the voltage control relay and used a sort of weak current bias to drop the output voltage if a high enough current was being drawn. The longer rectangular ones are typically the type with the adjustable current limiting built in.
Although many old charging systems didn't even have actual voltage regulators. Rather they just had the isolation relay and a specific value resistor inside the regulator box that just kept the generator at a proportional current output . The faster the generator turned the more amps it delivered. It was crude but still millions of them were used.

You are in fact right that they used a rather crude mechanical PWM of sorts. Thats probably why a basic comparator design works rather well. It uses the same basic effect as the mechanical system but is much faster and more accurate plus uses actual diodes and provids far better spike suppression than the buzzing contact regulation systems ever had.

Just some things to think about.

thanks great help, hopefully I can get my hands on his car soon and see what working conditions I'm under

 

[bountyhunter]

I beleive 12 volts

I'm not really that concerned about the headlights etc because the generator (dynamo) will make what it makes and thats that, I'm interested in regulationg the output to preserve the battery, he may want to fix this device to all of his cars and possibly some of the ones he works on

You need to define the dynamo's control method. Modern alternators vary the current in the field winding to control charging current. Very old systems used permanent magnet generators and you have to use either an SCR controller or a shunt system. You better get the specs on the alternator first off.

 

[Thunderchild]

yes that's what I have said to him, I need to know about the generator he has