circuit opinion

[Bruce S]

Circuit Opinion

Okay folks I have an interesting circuit to build and though it's somewhat of an easy one to build that I would get some opinions as to which one others may think would be best.

Here the story. As some have read here, I built a battery pack of our companies' e-trike. Well the individual that has the trike didn't keep the batteries topped off during the winter, so when he brought them in for a checkup with the new meter he couldn't understand way the voltage was only 2.5Vdc!.

Here are the specs.

Battery pack: 40Vdc 16Ah

Motor or load: 36Vdc max draw 600W

Now what I would like to do is to build an I.D. ten "T" proof circuit that he can put on the new battery pack to keep them topped off.

For me to redo the battery pack, he had to go get a small solar panel. I told him get the VW one, he come back with a ICP one.

Nice unit, using the new "Watts Up" meter, so far the max reading I can get are 18Vdc with a current of 300ma in full sun outside connected to a motorcycle battery that read 12.43Vdc.

Here my dilemma, I can take this panel and build simple little voltage multipliers and take the voltage up to 45Vdc and let the battery pack charge off that since the charge will be low enough not to have to worry about over charging.

The opinions I would like to know, and hopefully without to many flamesfº), is this do I just go with the simple circuit or do I make use of the transformer method?

I'd like to be a little creative with this.

I'm not as good as some on here, but I can wrap coils and wire is not hard to come by.

If I go the coil route do I go with a ferrite core, iron core, open/air core.

Size is going to be a small factor as this circuit will need to be able to fit in a small space.

Or do I just chuck the transformer idea, get a couple diodes, electrolytics and go with the multiplier idea. We're not talking high current either so for me the 1Amp stuff works out since I can get them free off old PCBs.

Thoughts? circuit designs?

Bruce S

[kitno455]

i am no electronics guy- and i dont know anything about this particular panel, but could it be dis-assembled, and have the cells re-wired in series? then you could get up to your 48+v with no converter losses.

allan

[ghurd]

How about 3 of the $10, 1.5W HF PVs in series?

Not as fun, but it would work.

G-

[kell]

Check out this link for a basic tutorial on all the basic

voltage converter topologies.  The boost converter is

the simplest.

http://schmidt-walter.fbe.fh-darmstadt.de/smps_e/smps_e.html

And then check this out for a self-oscillating flyback design.

It is an excerpt from somebody's answer to a query that I posted

on sci.electronics.basics

Click to expand:

     Bottom of:

     http://webpages.charter.net/dawill/Images/Induction_Heater_Draft1.gif

     Part of "Floating Supply Inverter".

     Q14, C27 (L2 optional), C28, R77, C28, erm, huh, I put two C28's on that

     schematic, and T4.

     Q14 was a ZTX651 but for your current requirement, a 2N3904, 2222, 4401 or

     anything else rated for the voltage will work.

     On the transformer, instead of a secondary winding, you can use a highspeed

     diode from the transistor collector to get the doubled voltage.  In this

     schematic, I needed an isolated supply, so I needed a secondary.

     The primary winding (labelled 20uH) should come to around 20-40 turns of

     fine wire on a ferrite transformer core.  The capacitor across it should be

     smaller, more like 0.01uF.  The feedback winding (going to the transistor

     base) should be 1-5 turns, depending on supply voltage and primary turns.

I went ahead and built this circuit.  I used the suggestion of tapping the inductor

pulses with a diode at the collector, which allows you to eliminate the transformer

secondary.  You still need the feedback winding.  You can use some junkbox inductor if you don't want to wind your own, and wrap a few turns of wire around it

for the feedback winding.  If you don't know the direction the inductor is wound,

you will have to try it in one direction and reverse the sense of the feedback

winding if it doesn't work the first time.  When you do this, have a little lightbulb in series with the inductor to limit current, because it will short the

power supply to ground if the feedback winding is the wrong way around.  So you use the light bulb as a safety and a visual indicator of feedback winding sense (direction).

To get the boost you want may require trying different inductors.  I'm a little fuzzy on the dynamics of this circuit but if inductor saturation has anything to do with it, using a physically larger inductor will get you more voltage boost.  The actual inductance is not all that critical; I used a 46 uH toroid because that's what I had, and it worked fine.  It probably works with a wide range of inductances.

[Bruce S]

Allan;

  Not sure, it's a new unit and haven't had the time to disassemble the unit.

It does have a LED being used as a charging indicator and blocking diode tho.

Bruce S

[Bruce S]

Kell;

   Thanks for the links and ideas:-)

Bruce S

[Bruce S]

G-

  I'll go have a look at the HF stuff. I haven't looked at them since I saw the invertors they had costing more than the ones at a Pilot fuel stop.

But the weekends coming up.

Thanks

Bruce S

[Nando]

Bruce;

Your idea is simple and the easiest way it to get a boost circuit to build the voltage high enough to be above battery bank voltage.

A variable higher voltage current source equivalent circuit.

There are many Integrated Circuits that can boost the voltage,

Notice, you have a solar panel that needs to be detected power wise to convert the power to 36 volts to charge the battery bank.

The circuit could be simpler if you do not care for MPPT ( Maximum Power Point Tracking) but average power, ( about 10 to 20 % less power).

A simple voltage divider applying AC ( 3 to 6 Hz) to the current reference to vary this current to make sure to maintain the highest battery voltage under load.

Nando

[drdongle]

Keep it simple use 3 of the ICP panels in series