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Propeller Professional Development Board Power Supplyh — Parallax Forums

Propeller Professional Development Board Power Supplyh

scurrierscurrier Posts: 32
edited 2010-10-22 18:30 in Propeller 1
Hello all,

A couple of questions on the power supply for the Prop Dev Board:
1. Can someone link me to the Parallax product page for this power supply? I am having a heck of a time trying to find it.

2. I have a whole bag of adapters here and I'm sure I have one that meets the requirements for powering this board. What can I do to make sure that one that I pull out of the bag is appropriate? I saw the voltage requirements but I also saw some warnings about overpowering or something. Do I simply check that the voltage is within range even when the supply isn't loaded? How do I ensure that voltage won't dip too far when it is loaded? I have a volt meter to test with.

Thanks,
Shaun

Comments

  • eod_punkeod_punk Posts: 146
    edited 2010-10-20 16:22
    7.5 VDC 1 amp
    http://www.parallax.com/Store/Accessories/PowerSupplies/tabid/165/CategoryID/39/List/0/SortField/0/Level/a/ProductID/73/Default.aspx

    12 VDC 1 amp
    http://www.parallax.com/Store/Accessories/PowerSupplies/tabid/165/CategoryID/39/List/0/SortField/0/Level/a/ProductID/75/Default.aspx

    I would suggest checking any supply you have with your multimeter before hooking it up to a board just to make sure it hasn't gone crazy.
  • $WMc%$WMc% Posts: 1,884
    edited 2010-10-20 16:27
    scurrier wrote: »
    Hello all,

    A couple of questions on the power supply for the Prop Dev Board:
    1. Can someone link me to the Parallax product page for this power supply? I am having a heck of a time trying to find it.

    2. I have a whole bag of adapters here and I'm sure I have one that meets the requirements for powering this board. What can I do to make sure that one that I pull out of the bag is appropriate? I saw the voltage requirements but I also saw some warnings about overpowering or something. Do I simply check that the voltage is within range even when the supply isn't loaded? How do I ensure that voltage won't dip too far when it is loaded? I have a volt meter to test with.

    Thanks,
    Shaun
    '
    Try this
    http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/75/Default.aspx?txtSearch=power+supply
    '
    2.1mm jack center + POS....outer is - NEG
    With a voltage of 6volt DC to ~20volts DC and at least 1 amp
  • scurrierscurrier Posts: 32
    edited 2010-10-22 16:45
    I'm sure that a lot of people already know some of this stuff but I'm worried about my board so I'm being careful. Here's my explanation of what I'm doing for future reference. I have read a few things and it sounds like I will be OK with my power supply that I have. I'm just tested without the Prop plugged in. The power supply is rated 12 volts (1 amp) and found that with no load it was putting out about 16V. I was worried about this since the board says 7-12V on it.

    I plugged it in and turned on the board. It now reads 15.04V across the ground and input pins of the LM1086 regulator. Looked at the output of the regulator and that was 5.05V or so. The output of the downstream regulator was something like 3.32V.

    These regulator outputs sound correct so I'm thinking that my input voltages being higher than what I'm confident of should be ok. I haven't seen anything that was inconsistent with the LM1086 datasheet as far as input voltage or allowable voltage difference between input and output. I am thinking that the LM1086 would be the problem component in this chain if I went too high in voltage.

    LM1086 datasheet: http://www.national.com/ds/LM/LM1086.pdf

    I also just measured what the Propeller Education Kit regulators are putting out. The first one is putting out more than 6 volts and the second one is doing 3.33V. This gives me confidence that I am going to be alright.

    I'm going to try it with the prop plugged in and hope that my due diligence here has protected me from damaging the board. I wonder why Parallax recommends the 7.5V 1 amp supply? I'm just a lowly mechanical engineer... maybe some of our electrical oriented friends can chime in here?

    Thanks,
    Shaun
  • Mike GreenMike Green Posts: 23,101
    edited 2010-10-22 17:11
    There's a 5V regulator followed by a 3.3V regulator on the PPDB and also used in the PEK. Any input voltage in excess of the 5V produced by the 1st regulator is turned into heat. With a 12V regulator, that can be a lot of heat if you're drawing much current. Given that the regulator is spec'd for 1-1.5A, that could be 10 to 15W of heat with a 10V input excess (15V). That's a lot.

    A 7.5V "wall-wart" results in only a 2.5V input excess and the heat dissipated would have to be only 2.5 to 3.7W, a bunch less.

    That's why Parallax recommends the 7.5V power supply.
  • scurrierscurrier Posts: 32
    edited 2010-10-22 17:50
    OK guys. So I can't fully confirm that the above works because as I was plugging in the adapter I was going to use, I found that I already had a different 12V adapter down there. This one was 2 amps and measured less than 13 when unloaded. So, I used that one which seems to be working well. I measured the outputs of the regulators though and they were the same as before. So, I think that I would have been fine with the old one, but I didn't want to take the small risk to try it.

    I'm still wondering why parallax recommends the 7.5 volt one. Maybe the regulator works less with 7.5 than with 12? Less heat dissipation?

    Edit: Just saw the reply above. I'll respond in the next post for cleanliness.
  • scurrierscurrier Posts: 32
    edited 2010-10-22 17:54
    Mike Green wrote: »
    There's a 5V regulator followed by a 3.3V regulator on the PPDB and also used in the PEK. Any input voltage in excess of the 5V produced by the 1st regulator is turned into heat. With a 12V regulator, that can be a lot of heat if you're drawing much current. Given that the regulator is spec'd for 1-1.5A, that could be 10 to 15W of heat with a 10V input excess (15V). That's a lot.

    A 7.5V "wall-wart" results in only a 2.5V input excess and the heat dissipated would have to be only 2.5 to 3.7W, a bunch less.

    That's why Parallax recommends the 7.5V power supply.

    OK, this is something along the lines of what I suspected. Sounds like I should be OK with what I'm using now, though. Please tell me if I'm wrong. The 5V regulator is a bit hot, but I bet the junction temp is still ok.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-10-22 18:29
    Hang light bulbs in parallel with the input, that'll load/downreg your wallpack. "Retro" yet practical, light and some heat beats just heat.
    Just throwing that out there.

    PE - Depending on the rating and the bulb and all, it could be like a meter, too. ("Hey, whatever just happened made the bulb dim out like...")
  • $WMc%$WMc% Posts: 1,884
    edited 2010-10-22 18:30
    scurrier wrote: »
    OK, this is something along the lines of what I suspected. Sounds like I should be OK with what I'm using now, though. Please tell me if I'm wrong. The 5V regulator is a bit hot, but I bet the junction temp is still ok.
    '
    Can't really tell the temp of "a bit hot", But if you can keep your finger on the REGs you should be OK.
    '
    My voltage REGs run around 90'F with a lite load on the Prop. Pro DEV.Board.
    '
    I think you'll be OK with your wall-wart.(as long as you can keep your finger on the REG's with out getting burnt.)
    '
    Asking what might seem stupid questions will preserve the life of your Pro.Prop.DEV.Board.
    '
    Enjoy
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