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Arlo Batteries and Charging — Parallax Forums

Arlo Batteries and Charging

fataldavefataldave Posts: 61
edited 2014-01-11 11:31 in Robotics
Right now I have a small 12V 5AH battery I am using for Arlo. I am looking to replace it with two 7AH batteries. In a post or two I saw that Ken recommends a Power-Sonic PS-1270 battery. I was wondering if it would hurt to go with a 9AH PS-1290 or 8AH PS-1280 instead? Are there any negatives for using a larger battery? Sizes are exactly the same, there is a 1/2lb weight increase but with a payload max of 60lbs on Arlo this is not bad.

Second question is how do people charge the batteries? I have not mounted the current one so I have been pulling it off and putting it on a small 1A charger. When these new batteries are all wired and mounted this will be a bit harder to do. Do people just unplug the wires on the battery terminals and charge them one at a time? This might be an advantage of a bit larger 9AH battery less time between charges...

Thanks,
Dave

Comments

  • Ken GraceyKen Gracey Posts: 7,387
    edited 2014-01-11 08:28
    Hey Dave,

    Actually, I wish more people viewed the Arlo's flexibility in the way you do. There's no reason you can't use other batteries, like the PS-1290 or PS1280. You just need to make sure they fit in the battery tray, if that's where you plan on placing the battery. One benefit of using a larger capacity battery is that you could get plenty of operating time from one power cell, have less wiring, and easier charging. Any weight increase you add is not relevant in the small amounts you're talking about. The MMWK aluminum carries 50+ lbs. and easily 20 lbs. for the molded plastic version.

    Just be sure to check the dimensions of the Power Sonic batteries to see that they'd fit in that tray. The only reason the PS-1270s were initially chosen is because they seem to be available everywhere. And the 12V 7Ah size is quite standard - we see them in Fry's Electronics, MicroCenter, and Batteries Plus from other suppliers. They're commonly available, and cheap! Two of them fit perfectly on the Arlo's battery tray.

    Charging. I think I have the best method for charging: use a bench power supply. Set the power supply at 14.4V and charge it up until it draws less than 0.020 A. Limit the current to C/2 or around 3.5 A at this voltage for the PS-1270. This just gets the job done. There are many chargers you can buy and they have more capability, like they'll charge it up to 14.4V and then float to 13.8V, which is more accurate according to the PS-1270 data sheet. If you discharge them in parallel, you could also charge them in parallel if they're at the same voltage level. One benefit of lead acid batteries is their big resistance and fairly simple charging requirements.

    There's a convenient add-on we are making for the Arlo - a power switch plate. It won't be available for quite some time, but it'll support the use of a wall-power inverter power supply with a 2.1mm jack. These chargers source less current than a bench supply as far as I know, so it takes longer (trickle charger?).

    Somebody else should hopefully corroborate what I've said above. I mostly tote spreadsheets and business software, and rely on smart people to write my code and help me with electronics.

    Ken Gracey
  • fataldavefataldave Posts: 61
    edited 2014-01-11 10:04
    Thanks for the quick reply Ken. I didn't figure there would be a problem. The specs say they are all three the same size but I will try to find actual data sheets to verify since the site could be wrong.

    As for charging I have a small 1A SLA charger, I will just use that and unplug each battery to charge them. Just wanted to put it out there incase someone had a really neat method of doing it.
  • fataldavefataldave Posts: 61
    edited 2014-01-11 10:07
    Ken Gracey wrote: »
    If you discharge them in parallel, you could also charge them in parallel if they're at the same voltage level. One benefit of lead acid batteries is their big resistance and fairly simple charging requirements.

    Oh this will help out a lot! I didn't know that.
  • NikosGNikosG Posts: 705
    edited 2014-01-11 11:04
    fataldave wrote: »
    Second question is how do people charge the batteries? I have not mounted the current one so I have been pulling it off and putting it on a small 1A charger. When these new batteries are all wired and mounted this will be a bit harder to do. Do people just unplug the wires on the battery terminals and charge them one at a time? Dave

    My design of the electrical circuit (on my Arlo based robot) in order to charge the battery is the following:
    (I ‘ll use only one battery)
    attachment.php?attachmentid=106085&d=1389466891
    I use a plug for the external charger (the plug will be somewhere on the robots chassis) so I don’t have to remove the battery in order to charge it. In order to charge the robot I must have the switches 2 and 3 off and switch 1 on.
    Although this method is not the perfect one I think works fine. I hope that parallax will make a board – circuit for charging robots like Arlo, Eddie MadeUSA etc. in order to deal this issue
    arlo_wiring3.jpg
    1024 x 2044 - 228K
  • Ken GraceyKen Gracey Posts: 7,387
    edited 2014-01-11 11:31
    Nikos has a nice, clean design.

    Hey Nikos, are you waiting for additional encoders from me? I knew we had corresponded a few weeks ago but I neglected to follow up. Your message must've gotten lost in a flurry of communication after Christmas.

    Drop me an e-mail and refresh me on your needs please.

    Ken Gracey
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