Electronics > Repair

Battery Tender touch switch problems...?

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Willys:
Hello folks, my first post, thanks for any and all help.

I bought a Battery tender that maintains 3 types of batteries with 2amp and 8amp capabilities. I purchased it for my lithium battery in my van. The problem I am having is with one of the touch switches. It doesn't work all the time. I have opened up the glued together housing carefully and have exposed the board and two touch switches. I do not understand how these switches operate or know when you touch the what seems to me a thick hard plastic case? The case doesn't flex to allow pressure to operate the switch. Then I thought maybe the switch uses your skin to make a connection but how through such a thick case?  The switches are round with what looks like a 555 timer chip on them . It also has 4 contact spots, one is 5V, second is Grd, third is SW1 and finally the last is SW.  There are only 3 wires running to the switch Black , white and orange.

The unit works when the switch works but if the switch is acting up then the unit will not switch to the lithium battery option.

Can someone suggest how this operates so I have some sort of idea on how i can solve this issue? Or ask me to supply more information, basically so i know what to give you in regards to what labels etc you may need to know what switch these are.

I know this is not the best way to describe things, but i have no other knowledge on how to explain to you what I am dealing with?

Again thanks for any help you can offer.

floobydust:
Welcome to the forums :)
Can you give a model number and pictures, any markings in the chip? It sounds like a touch (capacitive or maybe magnetic) switch system they are using.
It is sensing either of those properties I think, through the plastic housing.

Willys:
Thank you for your response....the unit part number is  p/n 022-0337-dl-wh

Willys:
Hopefully these help also..??
It is very hard to get a good clear pic as the camera always wants to focus just beyond or too close, augh...!!!...lol

Sorry.

floobydust:
That little circuit board PSL1 40x02 is very likely a capacitive touch sensor and a custom part to the Battery Tender.
The chip used on the other side could be replaced, it might be a TTP223.

The way these work, is on power up they calibrate themselves thinking no finger is nearby.
So if you power up the charger with your finger or hand close to the buttons, it will learn wrong and then never recognize a finger near it.
Check the board for dirt and flux or anything conductive, crappy glue included. That white glue is notorious for turning conductive with age, I would pick it off the switch board. I think the touch pad is the copper on the back side.

Something else that can affect the touch switches is electrical noise.
These chargers do wear out their electrolytic capacitors, which makes more noise and causes erratic operation.
If you can get your camera to focus on the object and not the background, pictures of the main board can show fractured soldering joints (also a common problem) or bulged top prego capacitors.
There is a chance the switches work fine but there is too much noise for them.

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