Ryobi charger

[Nigel Goodwin]

OK, we've got a small Ryobi cordless screwdriver/drill at work, and the charger has just died - the primary read O/C across the mains input, so I took it to pieces to have a look. As expected, the wires go directly in the transformer, so I carefully peeled the insulation off to reveal a small heat fuse - thinking, it looks fairly easy (for a change) to replace. Anyway, testing it showed it was OK, and it's the actual transformer itself that is O/C

So I looked on Amazon for a replacement charger, to find a few 'alternatives' - all of which were actually 5V 2A Chinese power supplies, and not actually 'chargers' - the circuit of the original Ryobi one I've drawn out below.

The original obviously includes current limiting (the 4.4 ohm) and charging status (the LED), so I'm a bit 'dubious' about just using a 5V 2A power supply in it's place?.

I tried sticking 5V from my bench PSU directly into D1 and the centre tap, and then turned it up until the LED lit, while watching the current, and it took about 7.5V DC to make it charge correctly. After that attempt, I tried resetting the PSU back to 5V, and applied it directly to the output of R1, where it was taking about 250mA (although I've no clue as to the charge status of the tool). It's been running now about 1.5 hours, and it's down to 157mA, the red LED actually on the tool is still lit of course, so I'm keeping an eye on it, to see how it goes.

So what are peoples thoughts about it?, it strikes me as a bad idea just sticking 5V 2A directly in to it, although perhaps there's some kind of limiting inside the tool, as the red LED inside has to be monitoring the current somehow?.

Incidentally, we've ordered a new complete Ryobi screwdriver kit to replace it anyway - but that now uses a 5V USB type charger

 

[rjenkinsgb]

That looks nasty, more like an old, crude NiCd or NiMH charger.

I'd guess the screwdriver must have some limiting or protection in it as well, due to the charge voltage rating being well above the maximum cell voltage, and the original charger not having any cut-off facility..

I'd be tempted to try just 5V with a low value resistor (the 4.4 Ohm?) to keep the maximum current to within the 160mA specification?

Can you get to the battery to monitor the voltage directly across it?

 

[Nigel Goodwin]

That looks nasty, more like an old, crude NiCd or NiMH charger.

I'd guess the screwdriver must have some limiting or protection in it as well, due to the charge voltage rating being well above the maximum cell voltage, and the original charger not having any cut-off facility..

I'd be tempted to try just 5V with a low value resistor (the 4.4 Ohm?) to keep the maximum current to within the 160mA specification?

Can you get to the battery to monitor the voltage directly across it?

I could take it to pieces, but I'm not that interested

After about 4 hours the current was down to 99mA - but of course I've no idea what the original charger actually did?.

 

[Tony Stewart]

The battery aging rate significantly rises during time at CV levels vs CC so either keep a timer on it or lower the voltage. Smells like a 2S NiCd with thermal cyclic protection.

 

[Nigel Goodwin]

The battery aging rate significantly rises during time at CV levels vs CC so either keep a timer on it or lower the voltage. Smells like a 2S NiCd with thermal cyclic protection.

No, it's a Lithium battery, according to what it says on the tool. I suspect, like a lot of these kinds of tools, they don't pay much attention to proper charging. After a bit of googling, I managed to find a picture of it (and thus it's model number), it's a CSD4107 from 2009 - and clearly marked Lithium 4V.

 

[ZipZapOuch]

Ryobi never figured out lithium battery technology before the brand was licensed to Techtronic Industries (Hong Kong). Now, Techtronic Industries doesn't want to improve anything about the sub-premium Ryobi brand as their own premium lithium tool brand, Milwaukee, would seem less premium if Ryobi was close to the same quality.

I wouldnt touch a Ryobi tool with a 10-foot pole. No support, no replacement batteries, slow charging and questionable circuitry to charge the lithium batteries. It just doesn't seem safe to leave unattended while charging. I'd keep it on a concrete floor (or a large ceramic tile or in a ceramic flower pot) while charging to avoid spreading the fire.

 

[Tony Stewart]

Ryobi never figured out lithium battery technology

I have many such tools and no problems yet. Some chargers are faster than others. But like all LiIon tools, never drain dead and keep their without recharging. Charge complete shutoff and smart self-test seem to work fine on my models. 4V float might be OK

 

[Tony Stewart]

 

[Nigel Goodwin]

View attachment 141820

Yeah, it's relatively easy to figure out what type of battery you're charging, and alter the algorithm accordingly - yet another reason to use a micro-controller in them. Nice that it clearly labels what the LED's show - often it's only explained in the instructions, which you never see again

 

[Nigel Goodwin]

Well back at work today, switched my PSU back on, and it was charging at about 90mA - went away and carried on working - just happened to notice, the current has dropped to zero, so there must be some kind of charger/cut-off circuit inside the tool.