Charging problem

[Keoke]

Greg, on the Zenner ratings in watts. Divide the watts by circuit voltage to get amps. Eg., 50 watts/15 volts = 3.3 amps. Assuming your alt puts out 5 to 8 amps then two of the 50 watt guys are fine. Put three if you want insurance.
The ballast resistor is found on all GM cars with point type ignition systems. And you are correct in that they are made of ni-chrome wire set in a ceramic block. These are high wattage units. When at room temp they are about 1.5 ohms but when heated by current flow the resistance rises quickly. This is why they are called "ballast" instead of just regular resistors.
If you want to reduce current flow through zenner put another resistor in series (RT=3 ohms) with first one. If you want to increase current flow put another resistor in parallel (RT=.75 ohms) to the first one.

cheers,

 

[Keoke]

Keith, I agree with what your saying about the value of going around an OEM unit. Also, an automotive replacement VR is not likely replacement for I know of no auto alternators with a PM field. Every auto reg I have seen modulates field winding current.
The Zenner clipping circuit I drew is based only on a low amp (5) PM alternator.
Anymore amperage then that and the Zenner should now be used only to cycle the base on a high amp transistor and the excess wattage dumped through the Q's emitter/collector, high amp resistor and then on to gnd. Even this modified circuit has it's power handling limits.
On the OEM voltage regulator, other then triggering a charge light circuit, why in the world would a voltage reg have two modes for starting? Do you know??
On real heavy amp alternators the voltage regulator will turn off alt field current while cranking engine to take the alternators load off the starter motor. But, Greg's unit has a constant PM field.
Also, I think the open circuit (no battery in tractor) protection is unique feature. Good insurance for a tractor with PM alternator.

cheers,

 

[htiek126]

My comments about the circuit diagram are wrong if the VR includes an additional rectifier circuit. That would explain why Greg's VR does not have an additional wire for the voltage feedback from the battery.

When the battery is removed from the circuit, the VR does not have a good voltage feedback, therefore, the VR will lose regulation and the tractor accessories will receive the unregulated voltage from the alternator/rectifier circuit (which may or may not cause damage and safety issues, we would need to take some measurements).

I do not have my service manual with me, but this what I can remember. The VR has a starting mode for the zero rpm case in which the alternator is not producing (perhaps this is to reduce the load on the starter/battery). And then the VR goes into a slow rpm mode in which the alternator is hardley producing (I think the current is directed through some load in the VR, but not to the battery). Once the alternator is turning, it seems like the VR is always trying to keep the alternator output to pass through some sort of a load.

I have not had the opportunity or need to look at auto VR systems.

Keith

 

[normde2001]

This is getting awfully boring......It's supposed to be a tractor Forum, not rocket science.

 

[Soundguy]

"Putting 78xx and 79xx VRs in parallel is a bad idea. I am fairly certain that they will suffer from secondary breakdown without proper current balancing circuitry, however, it will work because of they are thermally protected. They will probably turn on and off like Xmas tree lights, and they will take turns running very hot. "

I realize they don't parallel well, but they are thermall protected.. and we are talking about a chargine system on a 20 something year old tractor.... And a limited capacity charging system at that.
In the beginning, I recomended a series pass regulator, but was unsure if a non-electrically oriented person would want to build a circuit with more than a couple parts from a schematic.

As for the relay.. I wouldn't even considder it... But if he wanted to spend some money.. a pulse width modulator and some irfz40's or cheaper irf511 mosfets will do a bang up job.. make some nice emi noise probably too.

"The wires in the 1110D schematic are not correctly connected to the full bridge rectifier. The Y wire should connect from the VR to point R on the rectifier. The R wire should connect from the VR to the + side of the battery. For the 186D, there is also a wire for the battery voltage feedback from the keyswitch to the VR and a lamp indicator wire output from the VR."

A couple of us noticed that as well.. the schematic, as posted would not have functioned 'as advertised'.


"Long story short, it would be an interesting project to build a VR, but probably not cost effective if you include the protection circuitry, additional modes of operation, and packaging. I am certain there are lots of alternate VRs available that would work great and cost less (like the Datsun one!), the trick is to find the information to cross reference and/or check the circuitry compatiability."


Pretty much same conclusion as well. FWIW I put a mitsubishi alternator (50 bucks), and an old style chrysler reg ( 10 bucks )on my ym1700 . Could have just as easilly put a gm job, and been done with it.... all self contained.

I knew I shouldn't have changed my major from electrical to civil... most of my 'fun' work is based around electronics anyway....

Soundguy

 

[Soundguy]

"A 12 volt regulator would not work at all since battery voltage, with engine running, is almost always above the standard 12.6 volts. "

I think you are missing the technical aspect of the idea. A 12 v battery can be charged to 6v with a 6v charging circuit..... A car battery that is normally sitting around 12.6 - 13.?? can be charged to 12v from a regulated 12v circuit like is being discussed here. In short.. the ambient battery voltage, after loading, will drop to what the maximum charge level will allow... it doesn't matter whether the battery is designed for 12.6 or 24..... if the charging source is 12... that's all ther is... and if there is a conductive path, and the batteries potential is less than the charging circuit ( i.e. after a load.. starting, etc )... curent will flow. ( we already determined that 12v is nearly on the unsuitable side of the scale... but as normde pointed out.. were not shooting for rocket science.. just something that keeps the tractor battery at a point where it starts when the key is turned... after all.. if the charging system is only rated at like 5 amps anyway.. they were'nt putting much time/effort in the charging system anyway... they just made a system that slowly replenished the storage cell in preperation for the next starting occourence... they obviously weren't planning to subsidize any extensive electrical circuits of any appreciable load..... anything over 5amps is a discharge situation...

Soundguy

 

[Soundguy]

""This is getting awfully boring......It's supposed to be a tractor Forum, not rocket science. ""

Normde.. it's a good thing that we aren't aaerospace. eng's.. as we might have taken offense at that /w3tcompact/icons/smile.gif

( are there any AS eng's out there... we seem to have a collection goint here.. electrical, civil, structural, etc... )

Soundguy

 

[Keoke]

Soundguy, I get Normde's point so this will be my last post on this subject.

In regard to your last post shown quoted below:

(I think you are missing the technical aspect of the idea. A 12 v battery can be charged to 6v with a 6v charging circuit..... A car battery that is normally sitting around 12.6 - 13.?? can be charged to 12v from a regulated 12v circuit like is being discussed here).

My reply is as follows:

A single wet cell fully charged (1.260/ 1.280 specific gravity) has static 2.13 volts per cell. This 2.13v times 6 cells = 12.78 volts for a fully charged battery. A 12 volt battery at 12.0 volts is less then 50% charged. Batteries continually kept at this low charge rate will die very quickly from sulphation of their plates.
In addition, there will be a voltage drop from where the VR ties into the alt to battery circuit so that when alt current finally get's to the battery it will no longer be at the VR's 12 volts but at a lesser value.
Bottom line, why would one want to design a voltage regulator that would keep a battery at less then 50% charged?
Also, if one was to put a fully charged battery in this tractor then, with tractor running, all loads would run off the battery (higher EMF) instead of the alternator until the battery is down to less then 50% of it's potential.
It doesn't cost much more, if any, to go a VR in the std 13.8 to 14.8v range so a VR in this range seems like a better bet to me for this application.

P.S., A quick rule of the thumb when converting battery voltage to battery strength is to add .25 to the true voltage (not surface chg) and take total of the last two digits in % of charge. EG. battery voltage is 12.4 volts so 12.40 plus .25 = 12.65 or a battery of approx. 65% strength. This formula is by no means super accurate but it is very close. You must use a digital voltmeter for this measurement.

 

[bruce1966us]

I have to agree with soundguy that the system is designed only to maintain the battery. We all know that a diesel requires no energy to run. This is why we are working with very small volts/amps.

Thanks,
Bruce

 

[htiek126]

The HEXFETS (IRFs) are a great idea, and you could just make it a steady state voltage reference/current limiting circuit. They have reversed temperture coefficients, therefore, you can put them in parallel without suffering from secondary breakdown (thermal runaway). I just built a special application battery charger with two IRF5305's (internal resistance = .06 Ohms and $1.60 each) in parallel, and they work great at dissipating about 75 watts of heat.

Keith