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8 Cell LiPo Voltmeter $2.79 — Parallax Forums

8 Cell LiPo Voltmeter $2.79

ercoerco Posts: 20,248
edited 2013-03-11 00:35 in General Discussion
http://www.ebay.com/itm/LiPo-Battery-Monitor-Low-voltage-Tester-Meter-Buzzer-Alarm-/310559391965?pt=LH_DefaultDomain_0&var=&hash=item484ec840dd

This just in: Ebay China electronics prices keep dropping! This 1-8 cell unit will be perfect for building into my new mecanum bot which uses 8 (!) Li-Ions to check each cell voltage. Reads up to 36V. The alarm feature is just icing on the cake.

I have used the 2-6 cell voltmeters previously: http://www.ebay.com/itm/RC-Voltage-Lipo-Battery-Meter-Indicator-2-6-cells-LED-W307-/360599301360?pt=US_Character_Radio_Control_Toys&hash=item53f564acf0 currently $2.11.

But for 68 cents more, I'm going for it. I have high expectations of this 1-8S meter.

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-02-23 21:30
    That looks geat!

    I don't know how I ever got by without those cool battery meters. I also like the LiPo alarms. This is a great combo. I've seriously concidered making a "Y" harness so I could attach both an alarm and a voltmeter at the same time.

    I don't have any LiPo packs with more than 6 cells but I don't mind the couple of extra pins.

    How can they possibly make these things so cheap?

    BTW, that alarm looks like the other alarms I've used which are very loud. I don't have a problem hearing the alarm go off when it's being flown on a quadcopter.

    Thanks for another geat find.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-02-24 06:14
    Have you considered that Lithium ion cells have an extremely flat voltage curve. Just using the voltage alone is not enough data to determine how much charge a lithium ion cell really has. At best, it can indicate when you are going too low on discharge or too high on charge.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-02-24 12:29
    Loopy Byteloose wrote: »
    Have you considered that Lithium ion cells have an extremely flat voltage curve. Just using the voltage alone is not enough data to determine how much charge a lithium ion cell really has. At best, it can indicate when you are going too low on discharge or too high on charge.

    It doesn't give a good "charge left" figure but it's helpful to know when you should stop discharging it. It's particularly nice to be able to monitor each cell since a single cell could be too low to safely continue using it and you wouldn't know there was a problem from just checking the overall voltage.

    It's particularly nice to have an alarm warn you when a cell is getting too low. I think a LiPo alarm is a "must have" item on a quadcopter. I generally stop flying before the alarm goes off but it's really nice to have the alarm in case I've misjudged the time the battery would be safe to fly.
  • xanaduxanadu Posts: 3,347
    edited 2013-02-24 19:20
    I have two of these, hobby stores stock them, they work great!
  • ercoerco Posts: 20,248
    edited 2013-02-24 19:30
    Loopy Byteloose wrote: »
    Have you considered that Lithium ion cells have an extremely flat voltage curve. Just using the voltage alone is not enough data to determine how much charge a lithium ion cell really has. At best, it can indicate when you are going too low on discharge or too high on charge.

    I would never accuse my $1.50 Ebay 18650 Li-Ions of having a flat discharge curve. :)

    Agreed, Loopy. No plans to use this as a recharge indicator, merely to look for low individual cells monitor overall voltage to correlate consistent robot performance.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-02-24 19:42
    Anyone know if these come with schematics or not? If not, how do they get wired up to a Stamp or Prop?
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-02-24 20:16
    NWCCTV wrote: »
    Anyone know if these come with schematics or not? If not, how do they get wired up to a Stamp or Prop?

    I don't think there's a digital signal to be tapped into. The only way I can think of to get digital information from these is to tap into the LED display. And translate the seven segments back to numbers.
  • ercoerco Posts: 20,248
    edited 2013-02-24 20:18
    NWCCTV wrote: »
    Anyone know if these come with schematics or not? If not, how do they get wired up to a Stamp or Prop?

    That would be the long way around. Using a dedicated ADC chip would be much easier.

    http://www.phanderson.com/printer/0838/0838.html
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-03-10 14:04
    Can someone explain how to wire these up? I just received mine and I want to test them. They have 9 pins, a a pos, neg and numbered 89, 79, 69, 59, 49, 39, 29 and 19. Obviously pos and neg fo to the battery. Do I just put another wire on the required voltage drop and connect it to pos?
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-03-10 15:11
    NWCCTV wrote: »
    Can someone explain how to wire these up? I just received mine and I want to test them. They have 9 pins, a a pos, neg and numbered 89, 79, 69, 59, 49, 39, 29 and 19. Obviously pos and neg fo to the battery. Do I just put another wire on the required voltage drop and connect it to pos?

    I received mine a couple of days ago. The negative pin is opposite the other battery monitors I have but agrees with the LiPo alarms I use.

    Those "numbers" aren't 89 etc., they're 8S, 7S, etc..

    The "-" pin connects to the black wire of your LiPo balance connection with the other wires connecting to the pins next to the "-" pin,

    For example my 3S LiPo as four wires leading to the balance connector. The wire colors are black, white, yellow and red. The black wire connects to the "-" pin, the white connects with the 1S pin, the yellow to the 2S pin and finally the red wire connects to the 3S pin.

    Sometimes the wires on the balancing connector are different colors but most of the packs I've seen have a black wire on the 0V connection. It's the 0V wire that connects to the "-" pin on the meter/alarm.

    These meter alarms can be left on a pack while it's in use but it will slowly drain a battery is left on for a long time. It's best to use it to measure a pack that you're actively using and not on a pack being stored.

    The normal "+" and "-" battery connections used to power devices isn't connected to the meter/alarm. The meter/alarm is intended to be used on the balancing connection.

    Here's a pack similar to my 3S pack. Notice the wires are different colors than what I described but the black and the read wires are the same as the pack I described. The small black wire on this pack would still connect to the "-" pin on the meter/alarm. Again, the larger red and black wires on the main connector aren't used with the meter/alarm.

    Are you planning on using your meter with a LiPo pack? If you use it with a different type of battery, you many need to figure out some sort of adapter.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-03-10 15:40
    OK. I see the 1s to 8s. My bad. So, I have Li-ion batteries which are in a 2 battery holder. It says to use 1s to 8 s for this and that Alarm is 2s to 4s. So, How would I wire to tell me if my 2 Li-ion batteries that I bought from @ercos deal of the day, 3.7v each are low and have the alarm sound? The devices have a push button for setting them but I am not even sure if the thing is working or not.
  • NWCCTVNWCCTV Posts: 3,629
    edited 2013-03-10 16:03
    I am still a bit confused here. I can get the display to show up when I use - on S1. The voltage range shows from 2.7 to 3.8v and Off. When I place the pos on S2 the alarm sounds no matter what I have the S1 set at. How do I "set" the voltage so when it goes below 7.5v the alarm will sound? Is that done on the Alarm S2 pin or what?

    Edit: Even when placeing + on S2 I am only able to go up to 3.8v. When using any of the other pins nothing comes up, only S1 and S2.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-03-11 00:35
    You don't use all the pins on the meter/alarm. You only use one plus the number of cells in your pack (n + 1 where n is the number of cells). For your two Li-Ion cells , you'd connect the 0V end of the pack to the "-" pin on the meter/alarm. The between cell connection connects with the 1S pin. The highest voltage connection of your pack connects to the 2S pin. I think the default on the alarm is to go off when any one cell drops below 3.3V.

    The pins 3S through 8S do not connect to anything when used with only two cells.

    Note, the pin farthest from the "-" is the 8S pin. The "+" symbol just indicates the plus side of cells works toward that end. There are nine pins on the meter/alarm "-", 1S, 2S, . . . 7S and 8S. There is no "+" pin.

    The alarm and meter use the same pins.

    I haven't figured out how to change the alarm settings. I'm hoping the default setting will be good enough for my needs.

    Sorry, I realize I repeated myself a lot and I'm sure I wrote things you already know. I wasn't sure what you were asking exactly so I just kind of gave a "shotgun" type reply (replying to everything I think you may have asked).
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