Electronic – USB plug adaptation for Dremel 7750

adaptercurrentdcplugusb

So, I recently threw out a bag of random chargers I didn't think I was using anymore. Later I found that my Dremel charger was part of these. I did however save all the connectors and just threw out the adapters, incase this would happen.

From what I can identify on images of the 7750, it is using a 5v 1650mA adapter, where the outer shell of the barrel is negative and the core is postive. Well I thought this would actually be quite nice, as I could wire it to a USB-A and just use one of my many AC-DC adapters, powerbanks, USBhubs… to charge it. (I have tried it using an old 5.2v 2.4a ipad charger, and 5v 2a oneplus charger)

So I did this and the light on the Dremel does light up red as an indication of it charging, but it never reaches max capacity (usually indicated by a green light if my memory is correct, and just turns off after a while). Once the light disappears I can turn off the power and turn it on again and the red light appears and seemingly keeps charging. After 10 minutes the Dremel is able to turn on and I can use it for a minute or so before it dying out. Leaving it for a longer period does not change the time.

I have attempted to use a cheap USB current reader, but it does not show any information, as if the current drawn is too low or something. I'm a novice in the field and would appreciate any explanation to why this is happening (:

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Best Answer

Looking at the specifications of that Dremel it seems to have a battery voltage of 4.8V using NiMH technology. Which sounds like 4 cells in series to me at a nominal 1.2V.

Now nominal voltage is not charge voltage to fully charge it the battery voltage should reach closer to 1.6V per cell or 6.4V for the device. The included adapter was probably unregulated so the voltage rose significantly above the marked 5V depending on load which would work as a dumb charger for NiMH probably sacrificing some life due to poor charging characteristics.

Your nice regulated 5V from your USB compatible adapters is not going to charge that Dremel. You need something that behaves more like the original adapter.