Charging Theory Question?

I’ve just built a WarSabers Starkiller hilt and the very impressive kit includes an onboard USB charging system.

If you look at the first diagram below, it shows how it works, using a TP4056 charge PCB.

It works great, except for two details:

The first is the red LEDs mentioned in the bottom paragraph on the diagram. They stayed lit the whole time the hilt was powered which was a pain, so I removed them. This leaves no charging indicator as such. Not a huge problem, but a niggle.

But the second problem is potentially more serious. I’ve read that TP4056 boards should not be wired such that the component load is being drawn at the same time as the battery is charging. However in this case, it is possible to do just that. If you leave the kill switch to ON and plug the charger cable in, the Proffie will be powered while the battery is charging, potentially, I’m guessing, confusing the TP4056 into thinking the battery is not yet full when in fact it is.

My theory knowledge isn’t good enough to know whether this is likely or if it’s an issue or not. For a project we might build for ourselves, it’s not a problem - we just have to remember to have the kill switch OFF for charging. But building a hilt for someone else, it really needs be bullet proof and idiot proof.

So it occurs to me that if I rewire the kill switch as per the second diagram, it can only ever be an either/or situation: either the battery is set up to charge and the Proffieboard is powered down, or the Proffieboard is powered up and the charging system is disconnected.

So my question is, would this work and is it necessary?

What have I missed?

Thoughts welcome.


Your second pic is what I’d do for sure.

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Been doing some more research and my wiring modification does indeed seem like the way forward. However I just noticed another anomoly: I took a partially discharged battery (which was reading 3.5 volts) and put it in the hilt, then connected the charge cable. Voltage at the battery terminals with the charge cable connected then showed 3.7 volts. But surely it should have shown 4.2 volts?

Shouldn’t it?

At the TP4056’s input from the charger, you should see charger voltage.
I don’t know those boards particularly, but I’d assume it’s “smart” and slowly charging the battery, so you’d only see a little difference at a time.

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