24 volt DC Power Meter question.

Discussion in 'The Projects Forum' started by Bumfuzzled, Mar 14, 2009.

  1. Bumfuzzled

    Thread Starter New Member

    Mar 14, 2009
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    0
    I am attempting to wire a Power Meter for a 24 volt DC scooter using a "Hope Sun" PM-2 Analog Panel Meter.

    The scooter has a plug used for charging that has +, - and ground. I straight wired it + to +, - to - and ground to ground.

    It has been a while since I have done any projects like this. :confused:Just before I was going to plug it in I got the feeling I had forgotten something:confused:.

    Can anyone tell me if this is the correct way to wire this or have I forgotten something?

    Thanks in advance,

    Bumfuzzled in Birmingham
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Post a diagram to see your circuit.
     
  3. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    DANGER, DANGER Will Robertson

    Good to ask because it's not clear to me what you have or trying to do. First there is no basic 'power meter' in that power is the product of two variables, voltage and current. To measure power one must be able to measure both volts and amps and multiply them, not something a simple single meter will do.

    Is you indeed have a current meter with built in shunt then it should NOT be wired + to + and - to - to the voltage source, this would just be a short circuit across the battery terminals and most likely would burn something up, the shunt in the current meter most likely or maybe the battery will explode. :eek:

    Anyway a true current meter is wired in series with one of the main battery leads such that all the current flowing from the battery passes through the current meter. Some 'current' meters are actually volt meters designed to wire to an external current shunt so there is no way to know exactly what you have or how it should be wired, but you should be cautious until it can be determined what you have. I was not able to find anything on google for "Hope Sun" PM-2. Did it come with instructions or a diagram?

    Lefty
     
  4. Bumfuzzled

    Thread Starter New Member

    Mar 14, 2009
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    0
    :(I have been trying to find a wiring diagram for this thing and cannot find one. It is a BladeZ PTV450. It is an older model but even the newer model refence material has only pictures of circuit boards and such. It appears that the charging circuit plugs into the circuit board but without a diagram on the board (and I have no idea if the boards are the same on the old model and the new) I am not sure anyone can help me. What I did on my end was pretty simple and straight wired as I indicated but past the plug on the scooter is the great mystery.

    If you or anyone hapens to know the wiring on this thing I would greatly appreciate it.
     
  5. Bumfuzzled

    Thread Starter New Member

    Mar 14, 2009
    6
    0
    Hi lefty!

    I thought that I might have had something wrong. The meter came with no instructions.

    What I want is a basic meter that I can watch and over time determine when I have 2/3 power and 1/3 power left in the battery. The idea being use 1/3 Touring, 1/3 getting back to the charger and keep 1/3 in reserve for emergencies and basically because I think these batteries work much better if they are not fully discharged when you recharge them.

    Since I have no wiring diagram for the meter or the scooter I may just be stuck. The only thing I do know is the plug on the scooter runs to a plug on a circuit board. Reading your post is stirring some old memories. I think If I had plugged this in that circuit board might have just blown and cost me a lot of money.

    Thanks for the warning. I guess until I can get some wiring diagrams this project is on hold.
     
  6. Bumfuzzled

    Thread Starter New Member

    Mar 14, 2009
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    A buddy of mine I e-mailed earlier just solved my problem if this thing will work. He suggested I put an accessory plug on the scooter and buy one of these: VECTOR 12/24 VOLT LCD VOLTAGE METER BATTERY TESTER. The next question would be; do they actually work or are they a $9.00 piece of junk. I guess I will be researching that tonight.
     
  7. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    Well if it's like this one http://www.amazon.com/Vector-VEC008-Digital-Voltmeter-Volt/dp/B0002ISEQW it should work OK and a heck of a lot safer and easier then trying to measure current. What you will be reading is the battery terminal voltage under load. You will have to determine over time what the 1/3 and 2/3 charge remaining points will be.

    Lefty
     
  8. Bumfuzzled

    Thread Starter New Member

    Mar 14, 2009
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    0
    :)That the one I am looking at. I claims to have: High/med/low voltage indicator lights show the battery's overall condition. I figure if I tour on high, return immediately on med and save low for emergencies I should be O.K. and like you said a lot safer and cheaper than trying to recreate the thing.

    I am just glad my pea brain engaged enough to tell me I needed to rethink my strategy. I may still have nightmares tonight about burning circuit boards.:(
     
  9. Bumfuzzled

    Thread Starter New Member

    Mar 14, 2009
    6
    0
    I have delt with the company that furnished me the Panel Meter a good bit so I wanted to pose the question to them: "Would the Meter they supplied work for a continous monitor of battery power for a 24 Volt, 12 A system and could it be wired as indicated in my previous posts?". They said that it is what this meter is designed for. They also indicated that to test one could start with a 9V then go to a 12V then the 24V system. In all instances, wired as indicated I should see the current voltage and get no smoke anywhere. I tried a 9V (As in Transistor battery) got 9V and no smoke and 8.9V reading. Then I took a 12V (As in a car battery) Got 11.8 and no smoke. Feeling pretty good about the info and results I tried the system for which I designed it. I was still a good bit apprehensive. It worked with no smoke showing 23.8V. After 30 min. it then showed 23.5V so there is some battery drain but the object is to insure that I get back to the charger before I run out of juice. So even though we don't know much more about the meter, we do know if you want to monitor battery charge it will work though it does cause some battery drain.

    Thnaks to those who offered input. It at least made me weary enough to double check before I made a smoke circuit.:)
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Bumfuzzled,
    Just so you know, the deeper you discharge your batteries (if they are lead-acid, as I'm suspecting), the shorter their life will be.

    It's best if you don't discharge them more than 30%. If you constantly run them down to 33% charge remaining, they'll have a very short life, even if you charge them right back up again.
     
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