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Using 18 Volt Tool Batteries — Parallax Forums

Using 18 Volt Tool Batteries

Bill ChennaultBill Chennault Posts: 1,198
edited 2012-04-29 09:58 in General Discussion
All--

In my next project, I would like to use an 18v battery compatible with my cordless tools. The 18 volt Ryobi comes to mind. But, my favorite motor controller--the HB25--has a 16 volt maximum input. I use gear motors that have a stated max of 15 volts with a stall current of 21A, but I am sure I have never drawn more than 3 - 5 amps. Of course, I also need to get some power at acceptable Propeller Vin levels, too.

Is there a practical solution using the Ryobi (or similar) battery or should I abandon that idea?

Thanks.

--Bill

Comments

  • W9GFOW9GFO Posts: 4,010
    edited 2012-04-27 10:19
    I think it is a good idea. Why not use 12V tool batteries?
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2012-04-27 11:00
    Hello Bill,

    What is the Ah rating the battery packs you want to use? Are they going to give you a long enough run time? On my larger robots I've been using SLA type batteries. I try to use standard sizes (7ah, 17ah, etc) so they are easy to get. On my latest robot I want overboard and went with a 55Ah battery but it can handle the weight and I wanted a long run time... With the 12V you can often use some of the smaller automotive chargers since many now have a setting for SLA batteries. If you stick with 12V you can use the HB-25's.

    If you stay with the 18V packs and can't use the HB-25's then you may want to checkout the Scorpion XL since it will handle those batteries and shouldn't have any trouble with the current.

    http://www.robotpower.com/products/scorpion_XL_info.html

    http://www.robotpower.com/catalog/

    Robert
  • ercoerco Posts: 20,259
    edited 2012-04-27 11:33
    +1 to SLA batteries for bigger robots. Cheap, readily available & very easy to keep charged. Weight isn't a huge penalty on larger bots, in fact sometimes the extra traction comes in handy. I've heard that they have problem with sulphation, but I have some smallish 6V SLAs that are still going strong 8 years later.

    http://www.ehow.com/how_5991322_rejuvenate-sla-batteries.html

    I found those cheapie Ebay NiMH batteries I posted about to be quite useful, even though they are really 900 mA cells. Easy to make any voltage by the number of cells, and easy to make a trickle charger out of nearly any old AC adapter. For several recent projects (robot arm and robot arm printer) I just use 4 cells for 5 volts direct in, no voltage regulator required.

    I have a lot of LiPo & Li-ion batteries too. They're lightweight and great in the right app, but charging Li-ions is problematic. Loopy Byteloose posted about some AA sized Li-ion's a while back, #14500. I like those, and the fact that you can put 'em in an existing AA battery holder is a plus. Just don't use them in an existing product made for AA cells or you'll see the magic smoke. 3 of those 14500 AAs drove my 12V relay board at Expo all weekend.

    http://www.ebay.com/itm/2-x-3-7V-1200mAh-ICR-14500-AA-Li-ion-Lithium-Rechargeable-Protected-Battery-New-/140651808043?pt=US_Batteries&hash=item20bf80452b

    http://www.amazon.com/Tenergy-Li-Ion-Cylindrical-Rechargeable-800mAh/dp/B003BHDP4C
  • W9GFOW9GFO Posts: 4,010
    edited 2012-04-27 11:51
    SLA batteries are fine and all but if the robot is small-ish, LiPos are a great way to go. A cordless battery pack has the advantage of being very quick to swap out, fast recharge and high energy density. If you use Ridgid, they even have a lifetime warranty on the batteries.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-04-27 11:52
    Well, you can always put diodes (if nec., stud mount rectifiers) in series, dropping "0.8V" per.
  • Bill ChennaultBill Chennault Posts: 1,198
    edited 2012-04-27 12:18
    Robert and W9GFO and erco and PJ Allen and All--

    The only reason I wanted to use the 18 volt Ryobi P103 is because my next door neighbor and I kinda sorta decided to standardize on Ryobi tools using that battery. (I'm sure that will change as soon as one of us sees the next, new, neat thing, or n3thing.) Twelve volts would sure suit my electrical requirements better. I just thought it would look COOL to be able to slap one of those Ryobi battery packs into my robot.

    The Ryobi P103 is a 24 watt-hour battery. I am not sure how to equate that with the two motors I want to use, which are my Banebot RS-545 gear motors. Perhaps the P103 is totally inappropriate, power-wise. I have been using dual, 12 amp hour, sealed, lead acid batteries. They are bulky, but provide all the power I need. (Far more, actually.)

    I do not have to use either the Banebot RS-545 motors or the Ryobi P103 battery. If I switched to the RS-775 18v (6v-20v) motor, then I suppose the Ryobi P103 would work from the voltage standpoint. (I don't know about amp hours, though. Maybe I would use TWO P103s. Now, that would look neat!)

    --Bill
  • kwinnkwinn Posts: 8,697
    edited 2012-04-27 15:44
    Bill Chennault wrote: »
    Robert and W9GFO and erco and PJ Allen and All--

    The Ryobi P103 is a 24 watt-hour battery. I am not sure how to equate that with the two motors I want to use, which are my Banebot RS-545 gear motors. Perhaps the P103 is totally inappropriate, power-wise. I have been using dual, 12 amp hour, sealed, lead acid batteries. They are bulky, but provide all the power I need. (Far more, actually.)

    --Bill

    The 24 watt hours would be 1.33 Amp hours (watt hours = amp hours x voltage), so pretty small compared to what you are using. I have used DeWalt 18V batteries to run my laptop for extended periods and that works pretty well.
  • Bill ChennaultBill Chennault Posts: 1,198
    edited 2012-04-27 16:00
    kwinn--

    Thank you for explaining it to me. And, you're right, that would be tiny compared to what I am using. I don't think even two of them would be sufficient for the motors I use.

    --Bill
  • ercoerco Posts: 20,259
    edited 2012-04-27 17:00
    Too bad those DeWalt 36V battery packs haven't dropped much in price. So much potential... I heard A123 has lawsuits aplenty going. Not quite ready for the "open source" crowd. :)

    Hacking: http://www.slkelectronics.com/DeWalt/packs.htm

    Refurb $124! http://www.ebay.com/itm/DeWalt-DC9360R-H-Duty-36V-NANO-Battery-Pack-WARRANTY-/180790716773?pt=US_Power_Tools_Batteries_Chargers&hash=item2a17f76965
  • kwinnkwinn Posts: 8,697
    edited 2012-04-27 23:24
    Bill Chennault wrote: »
    kwinn--

    ........And, you're right, that would be tiny compared to what I am using. I don't think even two of them would be sufficient for the motors I use.

    --Bill

    I am a bit surprised that a cordless tool battery would be so anemic. Not sure what my 18V DeWalt batteries are rated at but a charge is good for 2 to 3 hours of driving screws to mount hardware. When I used one as a substitute for my laptop power brick it let me use the laptop for a full 8 hour day.
  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2012-04-29 07:39
    kwinn wrote: »
    Not sure what my 18V DeWalt batteries are rated at but a charge is good for 2 to 3 hours of driving screws to mount hardware .


    I think those batteries are rated at 3 or 4 amp hour
    kwinn wrote: »

    When I used one as a substitute for my laptop power brick it let me use the laptop for a full 8 hour day.

    Where did you get the power cord for your laptop to use a 18V DeWalt batteries to power the laptop
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2012-04-29 09:19
    I have to wonder whether these "I8 volt batteries" are really operating at that level or it is just a lable. After all 12 volt lead acid batteries are running at 13.4 volts; Lithium 7.2 volt batteries have a rather loose range as well. Similarly 15 volt motors are likely to run fine on 18 volts -- just a bit faster. The real bottleneck is the HB-25 as I have no idea if the 16 volts in critical or just a ballpark figure. Most transistor and MOSfets are rated far about 16 volts (30 volts and above), so I am wonder if there is a voltage regulator that will overheat or the cooling fans will fail.

    The obvious solution is to build your own H-bridge out of TIP120s amd TIP125 or similar power MOSfets. Those 18 volt batteries are likely to charge to beyond 20VDC and then drop to something like 14VDC under loads.

    If you really want to use all that you have - the 18VDC battery, the HB25, and the 15VDC motors -- just get some large rectifier diodes (like 10 amp) and use them to knock down the 18VDC to 15VDC. At .6volts each, a series of 5 should do the job. But test that battery for its real peak voltage - never trust the lable.
  • kwinnkwinn Posts: 8,697
    edited 2012-04-29 09:58
    sam_sam_sam wrote: »
    I think those batteries are rated at 3 or 4 amp hour



    Where did you get the power cord for your laptop to use a 18V DeWalt batteries to power the laptop

    The connector to clip on the battery came from a dead battery charger and the cord and barrel connector to plug into the laptop came from a dead power brick. Recycling at it's finest. With a fully charged laptop and DeWalt battery I have been able to run for a full work day.
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