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Cordless Power Tool Conversion 18VDC to 120/240VAC

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Necessity is truly the mother of all inventions....and my case was no different.  About a year ago, I found myself with a dead battery for my Ryobi 18V cordless tools and no means of getting a new one as I was working overseas. So I came up with a setup to run my tools off AC (household current) safely and with no worries of my tools dying halfway into the job.

Now I enjoy all the benefits of battery operated power tools just as much as the next guy....They're convenient, flexible, and you can usually get quite an assortment of tools that run off the same battery.  Then the inevitable happens....you get the dreaded blinking set of lights on your charger and the batteries die out almost instantly. Your faced with two options.....Drop $50-$100 on a new set of batteries or try rebuilding them yourself.  Neither one of those two options appealed to me nor did I have the time to order the parts from overseas.  As anyone in my situation might do, I scoured the internet for an alternative solution.  I found guys connecting car batteries to their drill...ummmm no thanks.  Then I came across the idea of using an old laptop power supply in place of the battery.....The voltage seemed right, but alas the wattage was too small.  Even at 180 watts, the biggest pc power supplies couldn't provide enough to overcome the start-up current of my battery operated circular saw or angle grinder. 

The principal of the pc power supply was sound, I just needed something bigger.  After a little more research I found that the common everyday laptop power supply is what they call a "switch power supply".   Turns out, switching power supplies are very common everywhere in the world, affordable and come in a variety of voltage and power ratings... I eventually chose a 350w AC/DC power supply produced by a reputable company called Meanwell with a voltage range of 15-18volts DC.

Wiring of the power supply to a dead battery is very straightforward, but the following instructable goes through the details step-by-step.
 
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rijack1 year ago
Awsome idea! I've thougt about this for my DeWalt 18V machines.
How did you figure out that 350W power supply was enough?
Did you measure, or looked up via specifications, or...?
franco40 (author)  rijack1 year ago
Hi rijack,

As I mentioned in my instructable, I originally tried a 180W power supply from a high end laptop but it just bogged down with any load. I looked around the internet and found the 350W which gave double the amps. I figured 20Amps should do it and if it was overkill, it wouldn't be by much. The motors of the tools will only draw as much current as they need. My cordless grinder has the biggest motor....if it didn't stall under load then I'd be safe.

I plan on putting a Youtube video showing the setup in action. With that I'll put an amp meter showing the current draw at startup.

Hope this helps.
pc-fan franco401 month ago

I like this article, thanks for the instructable and the info in comments!

A friend gave me an 18V battery drill with exhausted cells for free and I would like to modify it to run from the wall outlet without spending much on an expensive power supply.

I have found some examples of utilizing spare components, could a pc power supply be modded for the task? Or maybe something similar that is easy to find? I have a dozen of these PC PSUs rating from around 200W to 500W though they provide 12 volts output.

Cordless Drill to Corded - Modify Cordless Drill to Run from Wall

Power supply to my old Skil 2972

Any ideas or recommendations? THX

franco40 (author)  pc-fan1 month ago

Hey PC-Fan.....As I mentioned in my instructions, I found a 350w supply to be powerful enough to cover all my tools. A bigger supply like 500w would do the same job as the tool only pulls what it needs. Now for your question about using a 12v supply vs a 18v, you can try it although your tools might not perform 100%. I would suggest if you want to utilize the 12v supply, get a stepping transformer to bump the volts to 18.

pc-fan franco401 month ago

Thanks for the tip and your quick answer, Franco40!
A suitable step-up transformer / dc-dc converter seems affordable (~15$)

You can wire transformers of the same voltage in parallel; I have also wired transformers in series to increase voltage. I WOULD NOT RECOMMEND THIS IN ANY APPLICATION THAT WAS LEFT UNATTENDED!

@jenkinsdan Thank you for confirming this option!

I have thought about this but a friend discouraged me saying that this would not be possible. Minutes ago, following your advice I found a nice tutorial about this:

Using Power Transformers In Parallel or In Series

Kinda hazardous how the host uses live electricity while connecting wires but the video is very articulate and comprehensible.

__

I would make sure to avoid it but what are the risks of leaving the connected transformers unattended? Heating and fire?

I think I will apply the safest, simplest, cheapest method available, but it is good to know that this would also work!

My personal favourite trick:
The cheapest source of suitable batteries is those sold for (serious) radio control models.

Take a cheap RC model battery pack with compatible voltage and capacity, and a matching plug.   Then make a five foot lead from the plug to the power tool terminals.

Then just drop the battery pack in your pocket, and conveniently use the power tool with much less weight in your hand.

And if it is a reasonably compatible voltage, and with an appropriate socket fitted, run it from a car battery charger when in the workshop.

If the car battery charger is a slightly lower voltage, the tool will run a bit slow.

If it's a higher voltage, the tool runs faster, but give it regular breaks to cool down or it will overheat !
RC battery packs are available with a wide range of discharge rates, indicated by a number followed by the letter C (e.g. 10C, 20C), where the number is the fraction of an hour in which the battery can be safely drained. For example, a 3000 mAh 20C pack can be drained in 1/20 h (3 min) and therefore can supply 1 A for 3 min.

Somebody please tell me if anything in italics was wrong, because I suspect that it was.
phase90 Ian011 year ago
Actually, the C rate is the drain rate that is a multiple of the capacity. The 3000 mAh pack that has a 20C rate means that it can provide 60 Amps continuous drain (3 Ah * 20). So, it can provide 3 Amps for 1 hour (3000 mAh) or 60 Amps for 3 minutes (60 minutes / 20 = 3 minutes).
Ian01 phase901 year ago
That makes a lot more sense. Thanks. :)
pc-fan Ian011 month ago

@DOTAU, @phase90, @ElectroFrank et al

OK, I have an 18V battery drill; the battery pack contains 15 pieces of cylindrical batteries with the text: "SC1.2V 1200mAh NiCd" – these look like the attached image. Their metal casing is rolled into paper.

How to properly calculate the parameters for a suitable power supply? amps, watts – I guess voltage would be 18V :)

What do the 'SC' letters mean?

I like this article, thanks for the instructable and the info in comments!

1_2V-1200mAh-rechargable-NiCd-battery.jpg

Hi pc-fan, NiCd means Nickel-Cadmium cells which are 1.2V, so 15 in series makes 18V. 1200mAh is the individual cell capacity (1200 mAh = 1.2 Ampere-hour). The battery pack is therefore 18V, 1.2Ah, when new it should provide (about) 1.2A for one hour. But drills can take more like 10A, if so you might (theoretically) get full power continuously for about seven minutes.

To discover the maximum current that could be taken by the drill, remove the battery and measure the motor's resistance with a multimeter. The maximum current taken will be the voltage divided by the resistance. So if the motor shows 3 Ohms resistance, 18V / 3 Ohms = 6 Amps, so you would need a DC power supply providing 18V at (at least) 6 Amps.

(If the drill has a speed control, you would need to open it up and disconnect the motor to measure it's resistance.)

An ordinary cheap car battery charger giving 12V at 5A would do some work, but at much reduced power (the motor could then only take 12V / 3 Ohms = 4 Amps).

Power rating in Watts = Volts x Amps. A power supply unit must be rated at or above the maximum current drawn by the appliance.

Hi ElectroFrank, thanks for your precise and practical answer, this helps a lot! I will do this.

(SC is probably just the manufacturer's code name for the type of part.)

DOTAU phase901 year ago
3 Ah * 20 C = 3 Amps , not 3 Amp hours
phase90 DOTAU1 year ago
3 Ah (3000 mAh) is the rating of the cell or pack. If it is one string with nothing in parallel, they are the same. That means that the item can provide 3 amp hours of energy. In an ideal world, it is 3 Amps for 1 hour, 1 Amp for 3 hours, etc.
The C rate is the highest rate at which the cell (or pack) can be drained per the manufacturer's spec. In this case, 20 C. This means that the max drain is 20 times the capacity rating of the battery. 3A * 20C = 60 Amps. It only has a capacity of 3 Ah, so its theoretical capacity limits it to 3 minutes (1 hour = 60 minutes, 60 minutes/20C = 3 minutes). The reality of cell chemistries is that you cannot get the full useable capacity of the cell/pack at discharge rates higher than 1C due to internal series resistance and other factors.
In practice, the effective capacity of a battery is less at higher discharge rates. At higher currents, more energy is wasted as heat due to the battery's internal resistance. That's why batteries get hot when charging or discharging.

Please can anyone provide a link to a table of those RC pack codes ?  That would be extremely useful.
That is true. Some cell technologies are better than others in this respect, but yes it is harder to get all of the gas out of the tank at higher rates. It is the price we pay for being able to use it quick.
What are RC pack codes?
The pack codes you mentioned about C rate, 10C, 20C etc.   Or was what you already said all the info there was on that ?   I just wondered if there was any more data that might not be obvious to those less familiar with the RC "scene".
The C rate pertains to the cell itself.
The only pack codes that I know of are the ones that describe the construction (# of cells, negative electrode, positive electrode, shape of cell, size (diameter, width, height)) as given in IEC 61960. This is a standard for secondary (rechargeable) cells for portable applications.
DOTAU Ian011 year ago
phase 90 doesn't quite have it correct

The "C" rating tells you how much current relative to capacity, "mil Amp hour", that is safe to draw or charge your battery.

Amps = C * m A h / 1000 ( the /1000 is to go from mil amps to amps)

So a 1200mAh 10C battery is good for 12A (10 x 1200mA/1000)
A 1200mAh 15C battery would be good for 18A (15 x 1200mA/1000)

Exceed this rating for to long and excessive heat and catastrophic failure will surly follow.
phase90 DOTAU1 year ago
That is basically what I said. Rating * C for max continuous current draw. However, the C rate does not apply to charging at all.
jeff827 months ago

Thanks for this. I plan on doing something similar soon. I was wondering about what power supply to use. I noticed that the one you got was a 15V and the device you are powering is 18V. Is there a reason why the 15V is sufficient? Would I be able to use a power supply as the following:

http://www.jameco.com/webapp/wcs/stores/servlet/Pr...

Thanks for your help.

Jeff

That power supply is only 1.7amps, which means you can only supply 30watts to a tool. Most of the ryobi tools are designed to run at around 48 watts, so you will suffer power drops with anything less than 3.0amps

whitcwa jeff826 months ago

Batteries have internal resistance. When heavily loaded, their voltage drops. A regulated power supply has very little internal resistance. So a 15 or even 12 volt regulated power supply is plenty of voltage for an 18 volt drill. A couple of years ago, I connected a 34 amp 12 volt supply to an 18 volt drill and it has plenty of torque.

The Jameco supply has nowhere near enough wattage for a drill. Dewalt sells drills rated from 130 to 750 Unit Watt Output

Thorn-Boy6 months ago

Whilst doing some digging looking for suitable parts for a homebrew device, I

discovered this beauty!

The eFuel 30A Power Supply (£80.00)





Your eFUEL switching DC Power Supply is designed to use household
AC power source to power equipments that required DC power. The eFUEL
converts standard household power 100-240V AC to 12-18V DC power and can
supply up to 30 amperes of continuous power.



FEATURES


  • Two DC power outputs, up to 30a
  • Output voltage adjustable 12-18V
  • Large LCD indicates voltage and current amperes output
  • Two USB ports, 5 volts, 1000mA
  • Smart cooling fan
  • Over temperature protection
  • Overload protection
  • Short circuit protection

Or, better still this:

eFuel 1200W (15-30v) 50a Power Supply (£180)





FEATURES



  • 1 x DC power output, up to 50a
  • 3 x 10a Outputs (On/Off)

    Output voltage adjustable 15-30V
  • Large LCD Display
  • Two USB ports, 5 volts, 2100mA
  • Smart cooling fan
  • Over current protection
  • over voltage protection
  • overload protection
  • Over temperature protection.

    Short-circuit protection (on output)





There is also a 'eFuel 1200W (15-24v) 60a Power Supply', but I can't find the specs on the website.

Thorn-Boy7 months ago

Just a thought, but has anyone wrote to Ryobi and asked them to make one?

What kind if price would you pay for a 'Ryobi' made transformer?

I can think of several benfits, but can you think of any more?

I'll list the ones I can think of, but please list any more you can think of:

* Abilty to use mains power when lack of mains power is NOT an issue.
* Longer use times for those with limited number of batteries
* During 'Mains Use' the tool would be lighter (less user fatigue).
* Extended battery lifespan (if batteries only charged when 'Going Remote').
* Less Battery Changes' if working near mains power.
* Less batteries required by user.
* Less batteries produced by manufacturer (better for the environment).
* More environmentally friendly (less dead batteries going to landfill).

My cynical mind says that the reason something like this has not been produced by Ryobi (or other manufactures for that matter) is that it would impact on the future sales of the consumables, namely the expensive batteries.

So how many batteries do you 'Ryobi' users actually own?

Personally, I have four (albeit NiCad) and several chargers, but find I need to swap around a lot when using a few tools at the same time.

These NiCad batteries will die soon though as I've had them a few years now.

Personally, I jump at the chance of a properly made transformer.

No offence intended OP regarding the 'properly made transformer' phrase. I just don't fancy the idea of building one myself.

I would make the jump to 4 x Lithium, but the cost is ridiculously high to get decent batteries when they are only for home use and I would rather have just a couple and a tranformer for when working near mains power.

Nice work by the way.

DICK WEED10 months ago

I've been thinking of buying Ryobi's hybrid string trimmer. If I do I'm going to take it apart and see what they did to make it able to run off batteries or AC. Might actually be cheaper and easier, especially the reconditioned ones.

http://www.homedepot.com/p/Ryobi-Reconditioned-ONE-18-Volt-Lithium-Ion-Hybrid-Straight-Cordless-and-Corded-String-Trimmer-ZRP2210/204593878

franco40 (author)  DICK WEED10 months ago
Hi DW,

Thanks for the comment....I wasn't aware Ryobi had a product with hybrid capabilities. Dewalt had something years ago for its 24v tools, but it didn't catch on I think. Is it a recent development? The price looks good considering what your getting. Let me know how you make out.

Thanks

Frank
DICK WEED franco4010 months ago
I Googled a bit and found Ryobi also had a blower that was a hybrid too, not sure that they still make it though. These seem a bit different than the DeWalt in that you don't have a special plug in battery pack, you just slide a cover that exposes a 2 prong AC "plug" while it covers the battery hole. And there don't seem to be a lot of extra electronics tucked in anywhere or at least not that I can tell looking at on line pics and definitely doesn't look like it has a fan to cool an ac/dc converter. I'm wondering if they went the other way and put in an ac motor and then the battery DC is switch to AC. My electrical prowess is pretty limited but the inverters for DC to AC usually seem pretty big too, so there doesn't seem like enough room for that. May go buy one from the local HomeDepot soon since new is only 10 bucks more than these refurbed and see what they look like inside.
vdv10111 months ago
Made it. Used it. Liked it. Thank you for this instructable!
danchanman1 year ago
I was wondering if a desktop power supply can be converted? But it only has 12v... Can it still work?
as an adapter for old tools that could be used on the bench it is a good idea I have been hanging on to some obsolete tools with dead battery packs now I have an option. A while back I while looking for something else I found out the RadioShack now sells many replacement batteries for many obsolete tools.
privatier1 year ago
Here is a cheaper source for your transformer: go to a place for recyling electronics and pick up a UPS. They contain transformers which are powerful enough. Connect the primary side to AC, and the secondary side to a bridge rectifier (35A, <$3), no capactor required. For long heavy duty work mount the rectifier on a heat sink. A CPU cooler from an old computer works just fine. Note that this solution has no inherent current limiter, so do not short the output!
Also, huge waste of time.
franco40 (author)  zappenfusen1 year ago
Hey Zapp,
You have a right to your opinion and I respect that, but to each their own. I'm sure there are guys out there that can make use of what I've instructed and that's why I did it. My needs overseas dictated I have a set of cordless tools. You might not be aware of this little fact, but consumers in the U.S. are privileged when it comes to availability and price of products. In southeast Asia where I'm currently working, you can't get a decent set of 18v tools for less than $1000!!! So I when I needed tools I brought them from the U.S. and I didn't want to drop a wad of $$$ on something that might get stolen on the job site. When the battery died, I improvised. Enough said.

I value and appreciate good well made tools just as much as the next guy, but my Dewalts, Porter Cables and yes....Milwakees stay home.
Franco40,
Sorry for the long winded reply & if I offended. I have been wiped out of tools several times in a 30 year career but if I can't use my tools for the purpose I purchased them they are waste of money. I have worked for contractors using my tools since the 1st theft and refusal of my employer at the time to replace them. I continue to supply my own tools with my employer supplying consumables. On the occasion I was relieved of a tool the cost of consumables increases accordingly. Maybe underhanded but have had no complaints from employers. Their insurance may not replace lost personal tools but they haven't seemed to mind replacing said tools through unexplained increases in consumable's cost even when my drill bit, blade purchases, etc. briefly rise to match cost of stolen tools. I guess I'm fortunate to be employed by persons appreciative of the fact I always have the required tool available without searching an entire job-site. I still believe purchase of cheap (Ryobi) tools beats the adaptation of PWM power supplies of adequate output to power a cordless tool. Please accept my apology,
Zappenfusen
I appreciate your reasoning and well know the sinking feeling when quality tools grow feet and are never seen again. $1000.00 for a rechargeable Lithium set-up would reduce me to corded tools also. The corded tools do have an appreciable increase in torque and speed over battery operated though and in your situation I believe, given the cost, I would stick with corded exclusively and invest in heavy duty extension cords. If job site theft is a main concern when purchasing, choosing, and comparing available tools I believe I would locate workmates a tad more respectful of others tools. There's nothing I hate more than a derelict attempting to sell stolen tools on a jobsite for 1/10 what they actually sell for. I'm adverse to the cost of the required XFMR to supply needed power for cordless tools. I have been fortunate that the majority of jobs I've worked on were inhabited by person's aware that my tools are my living and have respected that fact . Sorry If I offended yet I still feel converting cordless to corded kind of defeats the original purpose, convenience, and increase in utility of the new cordless offerings. In the States availability of High end cordless tool's is evidently 1/2 what you are paying in your locale giving great credence to your solution. I must insert I've a Milwaukee Magnum 1/2" Holeshooter which is 20 years old and will outlive every cordless I've ever purchased as will the Sawzall, Circular saw, etc., Eliminating the umbilical cord though will always increase productivity while decreasing frustrations to an extent making cordless indefensible when power isn't available. You would be amazed the situations absent of mains power making cordless necessary. Good things to be said for both but in my mind if theft dictates selection of needed tool I once again thank my lucky star's for the market I labor in. I will forever have my original corded Milwaukee's purchased when I realized the offerings of local Electrical contractors consisted of the cheapest tools they could find due to the conscienceless, thieving, tool less electricians (?) they insisted on hiring. When the manufacturer's developed cordless my 1st purchase of a Dewalt 14.4 volt drill, though Ni-cad, became my constant companion and now you would have a fight if you attempted confiscation of my newest Li-ion cordless tools. I'll never relinquish my corded tools as there's still jo
jobs they excel at (18" ships augers!), things only the outrageously priced and over the top 36 volt cordless are evidently meant for as well a stroking the Male ego. Sorry if I offended and good luck with those "footed" tools.
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