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Automotive 6 Volt Generator Transistor Voltage Regulator

rjenkinsgb

Well-Known Member
Most Helpful Member
You could use a hall-effect current sensor, which does not need a shunt - but then it's another device that needs power..
It does avoid voltage drops and heat though.

eg. One of these needs around 20 - 25mA at 5 - 6V and gives 0-5V out for 0 to whatever rating current:

There again, 5 milliohms at 25A is (I^2 * R) 3.125W - it should not be producing a lot of heat?
It should drop 125mV, I think you need a better resistor type.

Two of those open metal 10mR ones I mentioned early on, in parallel, would give you 5mR 10W, enough for over 40A?


edit - ps. While using a shunt resistor, the voltage sense should be from the battery end of the shunt, not the dynamo end.. Just spotted that on the drawings.
 

Danwvw

Member
Yes I was just working on Ideas for the shunt. I like the resistors the best but probably try to get it working with copper wire and deal with that later. But yes the shunt plays a very important role doesn't it. It's the source of the problem when it comes to keeping the same voltage output under various charging conditions.
If I set the voltage at 7 volts without headlights when the battery is topped off it doesn't go over the 7 volts,
If set to 7 volts with battery low it will gain 1/4 volt as the battery charges.
If set to 7 volts with the headlights on then with them off it will gain 1/2 a volt as it charges.
I am not sure I had the current limit set perfectly though.

NewProtoTypeProgress.jpg
NewProtoTypeProgress2.jpg


Ordered one of these, devices, If it's anything like the voltmeter it will work, It will be nice to mount with the voltage regulator, It's shunt will double as our shunt. It's only 50 mv though!
50AmpShuntAmpVoltMeter.jpg
 
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Danwvw

Member
Had some troubles with getting it working just wiring missing still then a shortNewPrototypeDesign10001.JPG then taking out a resistor. The way it test is to hook up all the (+ stuff) and the load (in my case a 6 volt LED Brake Light) to the + of two lithium ion's in series. The other end of the load goes to the DF wire everything else negative grounds.
Were now making all the Current Sense input voltage dividers 500 ohms instead of 1000. The 500 Ohm voltage adjustment pot is now a 250 ohm pot. And there is the 2 volt zener also the Motorola HDL Mosfet ! The E ic is switching with a pot setting of 100 ohms and the I ic is switching at 400 ohms on it's 10 turn 1K pot. It's ready to test on the Dynamo,
Has a 2 volt very high frequency oscillation on the gate at threshold.
Testing 21.jpg
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
Looks promising!
I'd not worry about the oscillation, the voltages are probably varying a tiny amount when the load switches.

The only possible mod I can see before it's tested is move the voltage sense (2V zener) to the battery end of the shunt?
 

Danwvw

Member
Well that would correct for any voltage drop at the shunt wouldn't it. But ideally there wouldn't be more than 50 mv if that is enough to detect? I should be able to measure that now with the test setup by looking at the voltage differential between pins 2 and 3 during switching by adjusting the current pot.
Looks like it can detect a change of 3 to 5 mv at the current inputs but through the voltage dividers it may a little less sensitive as they each cut the voltage in half.
 
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Danwvw

Member
Anyone know anything about cheap digital amp meters. This one has the Black Current lead Grounded. I was planning to use the shunt in the Positive D+ 7.55 Volt Circuit as my shunt. Is there a trick for floating the current inputs?
DigitalAmpMeter.jpg
 

rjenkinsgb

Well-Known Member
Most Helpful Member
That's annoying, though I don't think I have seen a combined unit with a "floating" current input, other than via a separate current transformer or transducer.

You could use two separate meters, or a programmable dual input meter, with one of the little current transducers I linked to earlier on.
eg. We use some little Lascar SGD-24M configurable TFT meters for various things, they are very convenient.

You can configure them for digital, bargraph, "analog" needle etc. and whatever colours and scale labels you like.

16ft_Pendant_sm.jpg
 

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