battery charger modification

hello, I am working on modifying a battery charging station for an 18v cordless drill (nicd) and I need some help the charging station is designed to be used with a standard 18v wall wort and I have modified it thus far to use a digital battery charger that will drain, charge, and cycle any battery I put against it (it will also read the temp of the battery and has auto cutoff settings) anyways, the charging station originally did not allow for draining a battery but only for charging, I have changed a bit of the internal wiring to allow for draining and cycling the battery. I have supplied pictures of the circuit board I am working with, the red and black wires go directly to the battery terminals, you can see in one of the pictures that I have de-soldered the red wire from its original point and re-soldered it to the positive lead of the power source comming in. this sorted out the initial drain problem, the new issue is something as a direct cause that I overlooked and that is now the led wont light up (due to an open circuit) I am thinking of returning the red lead back to its original solder point (across from the led) and adding in another lead from the power source to the positive battery terminal and placing an 1N4007 diode inline on that one so that the battery can be drained through that lead but charged through the circuit. I would like to know everyones oppinions on this if this is the correct route to take or not, if you would like me to whip up a schematic of the circuit I may be able to do so, just state which software it is needed for and I will see if it is installed or not, I do have several different softwares that I can make the schematic in. thanks

As simple as the circuit appears, a schematic would be very useful. I use TINA, although LSpice is a fav on the forum.

The sim software used is not really relevant.

Just give us a "before" and "after" set of drawings.

Just a pencil drawing of the schematic would be plenty for this.

ok so its been a couple weeks since I have had some time to do anything on the computer, I have been a bit busy with work and family (2hrs a day with family the rest of the day either working or sleeping) but here are the schematics as requested, the schematic on the left shows the original circuit before the modifications and the one on the right is the schematic after modifications. I am sure the final changes to the schematic are simple and probably already in my mind but I am not sure if they are the correct course of modifications so what ever everyone else brings to the board for these modifications will be taken into consideration when I look into buying the final peices for the modifications, I wont be buying them untill I know what I need for sure

Hi,

What are you trying to do here? You want to charge the battery and be able to drain it from the same connection point?
What is the LED for? To indicate charging or indicate discharging (draining)?

the schematic is the original circuit and the led indicated the battery was charging. The objective is to be able to use all of the features of the the digital charger while keeping the functionality of the original circuit which of course includes the led

Hi,

That schematic does not appear to be correct. Can you go over it to verify?

Oh ok, it appears that you are indicating the (perhaps wall wart) charging power source as the 18v 'battery'.

If you are using a new charger that puts out a DC voltage then it may be ok to simply short the diode in your first schematic that connects to the 18v power source drawn as a battery.
The original power source might have been an AC power source so it needed a diode, or it needed a diode to prevent reverse conduction in case the power went out.
If the digital charger doesnt have this problem, then you can short the diode. If the charge current is the same, the LED should still light up ok. However, if the discharge current is higher it might be a good idea to connect a protection diode across the LED in reverse so that during discharge the LED reverse voltage does not rise too high (LED's can only stand about 5v reverse voltage).

V1 and V2 is the barrel connection to the charger circuit, the digital charger puts out a DC volage only and without power will break the connection to the battery as to neither charge nor discharge so returning the connection back to its original solder point and bypassing the diode and then adding a reversed diode to the led should be fine.