# Looking for some circuit addition help

#### george0039

Joined Oct 15, 2008
167
Hello
I found this simple charging circuit for a hobby use. From a battery pack of 4-AA batteries through a voltage regulator TLV2217 and a reed switch N.O.N.C SPDT it charges a capacitor 3F/2.7v which then drives a mini coreless motor.

I would like to know if there was a simple way of indicating with a LED that the circuit has started charging, if not, no energized LED and another LED to show charging is done. That way I know there is No way to damage the capacitor.

Here is the simple circuit without those extra LED functions.

#### Tonyr1084

Joined Sep 24, 2015
4,502
A phone charger puts out 5 volts. You want to use it to charge a capacitor? Your drawing shows the motor in parallel with the capacitor. Not sure how you've hooked up the reed switch, but from what I know of them, one side is a single lead common to the circuit. The other two wire end is (one) N.O. and (one) N.C. You didn't show a magnet doing anything to actuate the switch, nor do you show what connection on the switch you're using to charge the cap through. Gonna be real tough to give you good advice.

If you want to charge the cap, then use the reed switch to run the motor from the cap - if your cap is rated at 2.7 volts and you try to charge it with a 5 volt charger you're going to blow up the cap. I'm not familiar with the regulator you mention so I can't really advise you on how to hook it up or into your circuit. But just from what I DO know, reed switches aren't intended to carry motor current. They're just not strong enough. Not unless you've gotten some sort of industrial reed switch.

#### george0039

Joined Oct 15, 2008
167
Here is the video that this circuit was also supplied from. Have a look and pause the video at the start to see parts list and circuit drawing.

All I wanted to know is if an LED can be added to indicate if the circuit is connected to the torpedo and charging it and also another LED to show charging is done.
Have a look at the link:

Thanks
George

#### Bernard

Joined Aug 7, 2008
5,520
Seem that it can be done. Maybe 2 comparators, one to detect a voltage drop across 5 ohm resistor & second
one to indicate 2.7 V. No time today.
Looks like a magnet holds switch in charge position, remove magnet & motor runs.

#### Bernard

Joined Aug 7, 2008
5,520
This may work, not tested. U1-A' s LED turns on when there is more than 20 mA flowing into Cap. Select
different values for R3 to change cutoff current. Could use to indicate full charge when LED goes out.
U1-B' s LED comes on when V on cap. comes within about 50 mV of charging V.

#### george0039

Joined Oct 15, 2008
167
Hi
Firstly, Thanks for the fast reply with a circuit.
Secondly, Which points of the second circuit connect to the top circuit Charging Points +ve, -ve? What value Resistor is needed?

Im getting ready to put together a shopping parts list.

Any chance someone could check the circuit out to make sure it works as desired?
Would like to keep the extra circuit as simple as possible.
Thanks
George

#### Bernard

Joined Aug 7, 2008
5,520
What was Bernard drinking ? Reverse pins 2 &3, R3 to pin 2 & ground. Might increase R3 to 47K up to 100k.
depending on what cutoff current is desired. A old green LED, Vf. 2 V, was used with 180 ohm for R6, 360 ohm still a good average value depending on LED used. With a 1 F cap. LED came on for about 2 min. with R3 @ 100k.ie- fully charged.
Which R ?
All Charge Ports+ ( CP+ ) connect together, same for CP-.

Last edited:

#### Bernard

Joined Aug 7, 2008
5,520
Just to be clear top ckt. re drawn. Counting cap. leakage, 10 mA might be a reasonable cutoff current which
makes R3 56k. Leakage could be measured to give better choice of R3.

#### george0039

Joined Oct 15, 2008
167
Just to be clear top ckt. re drawn. Counting cap. leakage, 10 mA might be a reasonable cutoff current which
makes R3 56k. Leakage could be measured to give better choice of R3.
View attachment 152675
Hi
Slightly confused. Where is the 1F capacitor coming from? I listed at the start a 3F capacitor.
Also the value of R3 ?
Also with the original circuit at the start, I connect this +ve, -ve leads to those same charging leads.
As for LEDs plain green off the bench LED`s is Good for me.

Thanks for the help and answers.
George

#### Bernard

Joined Aug 7, 2008
5,520
3F yours, 1F mine.

#### Bernard

Joined Aug 7, 2008
5,520
The leakage on my 1 F cap. after 2 hours stabilized at 100 micro A so leakage may not a concern.
Make R3 56k for 10 mA or 100k for 5 mA cutoff current which either should be useful full charge.