magnetic amplifier battery charger circuit or...
magnetic amplifier battery charger circuit or...
I'm thinking of making a magnetic amplifier based battery charger. I have various 60Hz transformers that might be incorporated into it. I had ordered some pre-made chargers from China, but they never came, which I blame on the trade war.
Re: mag amp battery charger circuit
The way the design is so far, it has two transformers using half wave rectification, out of phase, to supply full wave charging voltage. It's more like a quasi magnetic amplifier.
However, I'm also now leaning toward not really having it be a magnetic amplifier circuit but using a transformer with a full wave rectifier and using regulated output possibly adjustable from 12.4 to 12.8 volts.
Originally, I was thinking of having it be a toroidal transformer that I adjust the turns in the secondary winding to put out about 9.8VAC, and then full wave rectify to output 12.6V peak DC (12.6VpDC), with 117VAC on the primary winding. But I want to be sure I can leave the charger continually float at 12.6VpDC for maximum battery longevity.
I realized that if the mains (power line) voltage goes up to say 120VAC, the output of such an unregulated charger would rise about an extra 0.3VDC.
However, I'm also now leaning toward not really having it be a magnetic amplifier circuit but using a transformer with a full wave rectifier and using regulated output possibly adjustable from 12.4 to 12.8 volts.
Originally, I was thinking of having it be a toroidal transformer that I adjust the turns in the secondary winding to put out about 9.8VAC, and then full wave rectify to output 12.6V peak DC (12.6VpDC), with 117VAC on the primary winding. But I want to be sure I can leave the charger continually float at 12.6VpDC for maximum battery longevity.
I realized that if the mains (power line) voltage goes up to say 120VAC, the output of such an unregulated charger would rise about an extra 0.3VDC.
Re: magnetic amplifier battery charger circuit
So, where does the 'magnetic amplifier' come in to all of this?
Certainly a simple regulator would be adequate
Certainly a simple regulator would be adequate
Len
“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)
“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)
Re: magnetic amplifier battery charger circuit
Regulators use amplifier circuits. I moved away from using the magnetic amplifier approach after checking into it and finding out that dynamic range is limited, especially tending to lack ability to have an idle output.
The type of regulator makes a difference for providing qualities like stable output rather than cycling up and down, and peak current output, higher being helpful for bringing up a very low battery quickly out of a low voltage state that can damage it.
The type of regulator makes a difference for providing qualities like stable output rather than cycling up and down, and peak current output, higher being helpful for bringing up a very low battery quickly out of a low voltage state that can damage it.
Re: magnetic amplifier battery charger circuit or...
I'm leaning back toward an idea I had earlier, maybe as more an experiment than anything. I got a variac that I couldn't use inside my place here because it had a strange defect of outgassing something very toxic feeling. But I could set it under the car hood for charging.
Well, I'm thinking of opening it up and disconnecting the input connection and transferring the output(wiper) to that spot in the circuit, adding on a 12V winding whose output could be adjusted a bit with the wiper location on the toroid, and also limiting the knob rotation for only a small amount of turn to prevent too low an input impedance.
I wonder if anyone thought of something like that in the past.
¹ I have now disassembled the variac to try to figure out how to fit in the isolated secondary winding. The toroidal core is capable of handling a 1000VA secondary. A secondary added to a variac would be able to output about a half the maximum VA rating of a variac. This variac is rated 2kVA max.
² Preliminary assessment is that if I put in 117V on the wiper at the point where 110V was designed to be applied, and the top output is given as 130V, that translates to about 17% adjustability, but I could definitely make it less adjustable and could probably get away with going the other way up to about 25% without the risking too much core saturation.
If I make it 10% adjustable, that gives about a 1.2V range. if I set the minimum at 12.4V at 117V mains voltage, maximum voltage with the wiper turned "down" would be about 13.6V, current capability of about 75A if I can squeeze enough secondary copper wire in there.
³ I think the secondary is going to be 11 turns of 12AWG Romex®. I might try going to ten gauge though. The three conductors would then be placed in parallel and then full wave rectified. I calculate that will give an output adjustable range of 12Vdc to about 14.5Vdc. The latter might be used for start assist or quick charge (used with discretion).
⁴ I forgot to account for the voltage drop of the bridge rectifier. So the output could only reach 11.6V max (using 0.6V drop silicon diodes) since I measured the output as 9.25VAC with the knob set at max output voltage. But by using synchronous rectification, it could still work, and the max voltage could reach 13V.
Further evaluation (this is an update to note ⁴), though, moves me away from the synchronous rectifier idea. It seems kind of hard to control them well. I recall experimenting with them, and how they weren't very easy to time turning them on and off.
I've been able get more sweep range of the wiper brush on the primary winding now. The secondary output now ranges from about 8.5 to 10.7VAC. 10.7VAC × 1.4 - 1.4V = 13.5VDC. The first 1.4 is the peak voltage from a (60Hz) sine wave. The second 1.4 is included because of the two 0.7VDC diode voltage drops in the bridge rectifier. That output voltage is obtained with the knob set to tap the primary winding at fewest turns in its range of motion. At that point, the transformer begins to hum slightly, indicating a bit of core saturation. Microwave oven transformers saturate more than that, I think. They draw more idle current and tend to hum louder.
Well, I'm thinking of opening it up and disconnecting the input connection and transferring the output(wiper) to that spot in the circuit, adding on a 12V winding whose output could be adjusted a bit with the wiper location on the toroid, and also limiting the knob rotation for only a small amount of turn to prevent too low an input impedance.
I wonder if anyone thought of something like that in the past.
¹ I have now disassembled the variac to try to figure out how to fit in the isolated secondary winding. The toroidal core is capable of handling a 1000VA secondary. A secondary added to a variac would be able to output about a half the maximum VA rating of a variac. This variac is rated 2kVA max.
² Preliminary assessment is that if I put in 117V on the wiper at the point where 110V was designed to be applied, and the top output is given as 130V, that translates to about 17% adjustability, but I could definitely make it less adjustable and could probably get away with going the other way up to about 25% without the risking too much core saturation.
If I make it 10% adjustable, that gives about a 1.2V range. if I set the minimum at 12.4V at 117V mains voltage, maximum voltage with the wiper turned "down" would be about 13.6V, current capability of about 75A if I can squeeze enough secondary copper wire in there.
³ I think the secondary is going to be 11 turns of 12AWG Romex®. I might try going to ten gauge though. The three conductors would then be placed in parallel and then full wave rectified. I calculate that will give an output adjustable range of 12Vdc to about 14.5Vdc. The latter might be used for start assist or quick charge (used with discretion).
⁴ I forgot to account for the voltage drop of the bridge rectifier. So the output could only reach 11.6V max (using 0.6V drop silicon diodes) since I measured the output as 9.25VAC with the knob set at max output voltage. But by using synchronous rectification, it could still work, and the max voltage could reach 13V.
Further evaluation (this is an update to note ⁴), though, moves me away from the synchronous rectifier idea. It seems kind of hard to control them well. I recall experimenting with them, and how they weren't very easy to time turning them on and off.
I've been able get more sweep range of the wiper brush on the primary winding now. The secondary output now ranges from about 8.5 to 10.7VAC. 10.7VAC × 1.4 - 1.4V = 13.5VDC. The first 1.4 is the peak voltage from a (60Hz) sine wave. The second 1.4 is included because of the two 0.7VDC diode voltage drops in the bridge rectifier. That output voltage is obtained with the knob set to tap the primary winding at fewest turns in its range of motion. At that point, the transformer begins to hum slightly, indicating a bit of core saturation. Microwave oven transformers saturate more than that, I think. They draw more idle current and tend to hum louder.
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