| Author |
Message |
paul mcdonnell (Pmdpmd)
Member
Username: Pmdpmd
Post Number: 1
Registered: 11-2006
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| Posted on Sunday, November 26, 2006 - 3:27 pm: |
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I have a problem with my MD22. It worked apparently fine for about 5 minutes after I installed it. However, it then started sending out strange amounts of power to the motors which seemed to bear some relation to the inputs (I am using it in analogue mode), but not one I could identify. The switches are definately still in analogue mode (e.g. not in speed/steer mode).
I am only driving 5A motors, and I have a huge heat sink on the MOSFETs.
I checked the current usage and found it (i.e. the logic circuit) is using 400mA (compared to the 50mA spec) even with no motors connected. I also noticed the PIC getting hot.
The problem now exists even after I have let the PIC cool down for a couple of hours.
Has anyone got any idea what might be going on?
Thanks,
Paul. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 337
Registered: 10-2004
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| Posted on Sunday, November 26, 2006 - 5:58 pm: |
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Paul,
This does not sound good, what voltage are you using on the logic supply? |
paul mcdonnell (Pmdpmd)
Member
Username: Pmdpmd
Post Number: 2
Registered: 11-2006
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| Posted on Sunday, November 26, 2006 - 8:08 pm: |
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Thanks for the quick reply.
I am using 5v.
I originally used a 9v battery through a L7805 regulator, and I also tried it using 5v from my bench PSU. Same results I am afraid. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 338
Registered: 10-2004
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| Posted on Sunday, November 26, 2006 - 9:59 pm: |
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No problem, easier to answer questions quietly in the evening then during the day. If you return the controller back to us, we will send it away for a diagnosis. The manufacturer is very good and can quickly identify the cause of failure. You can find our address from a link on our home page, please include a note of the problem or even a printout of this thread. |
paul mcdonnell (Pmdpmd)
Member
Username: Pmdpmd
Post Number: 3
Registered: 11-2006
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| Posted on Tuesday, November 28, 2006 - 11:58 am: |
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Thanks - sent it off yesterday.
The heat sink I was using for the MOSFETs would have shorted out all the tops of them (the tags on top of the MOSFETs with the holes in them), for both channels. Could this have been a problem? |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 340
Registered: 10-2004
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| Posted on Tuesday, November 28, 2006 - 7:33 pm: |
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Paul
Controller received today and will be sent off tomorrow. The FETs are plastic bodied so no, this was not the direct cause of failure. |
paul mcdonnell (Pmdpmd)
Member
Username: Pmdpmd
Post Number: 4
Registered: 11-2006
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| Posted on Friday, December 1, 2006 - 12:24 pm: |
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Thank you, I look forward to your analysis.
I bought a replacement from you (as my project has literally ground to a halt without a speed controller!) which arrived today.
Before I plug this in to my robot, have you got any advice as to what I might check in case the problem is external to the MD22? I don't want to damage another one if it is something stupid I have done.
Paul. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 343
Registered: 10-2004
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| Posted on Friday, December 1, 2006 - 9:56 pm: |
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Paul,
I would suggest keeping it simple at the start, use a 4.8V NiCd battery (or 3 x AA ordinary primary batteries) for the logic supply, use your motors off load so you don't need the heatsink at this stage. It really is very easy to use, set your dip switches, ensure no polarity reversal on the battery supplies. You could use your mA meter to monitor the logic supply just in case. Connect your analogue inputs making sure the voltage does not exceed the logic supply.
That's about it really, do let us know how you get on. Your original controller should be sent direct back to you if it is a warranty repair / replacement and again if you could let us know here when you get it back.
Regards
Paul |
paul mcdonnell (Pmdpmd)
Member
Username: Pmdpmd
Post Number: 5
Registered: 11-2006
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| Posted on Monday, December 4, 2006 - 8:58 am: |
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Thanks for the advice. The new controller worked perfectly and I have been happily trundling round the garden this weekend! |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 344
Registered: 10-2004
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| Posted on Monday, December 4, 2006 - 6:52 pm: |
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That's good news, thanks for letting us know. |
paul mcdonnell (Pmdpmd)
Member
Username: Pmdpmd
Post Number: 6
Registered: 11-2006
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| Posted on Thursday, December 14, 2006 - 10:56 am: |
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Thanks for sorting this out Admin, I received a replacement MD22 a couple of days ago.
It looks like a new unit, so I guess my problem will forever remain a mystery!
The replacement I got previously is still working well - you are right, it is very simple to use and its working great from my laptop with a Vellemann USB i/f.
Cheers,
Paul. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 356
Registered: 10-2004
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| Posted on Thursday, December 14, 2006 - 6:18 pm: |
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Paul,
The manufacturer is very good which is another reason why we are pleased to represent them.
Regards
Paul |
tom walker (Tomjwalker)
Member
Username: Tomjwalker
Post Number: 1
Registered: 9-2007
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| Posted on Friday, September 14, 2007 - 9:09 am: |
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Hi Admin,
I am also using the MD22 with a Vellemann USB interface (using 2x analogue i/p), but I'm new at this so I've attached an image of how I intend on configuring the MD22. Can you take a look and verify that it is correct please.
Rgds,
Tom |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 578
Registered: 10-2004
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| Posted on Sunday, September 16, 2007 - 6:26 pm: |
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Hi Tom,
Yes that looks fine. Sorry but we are deleting your attachment as it is over 3MB, always best to attach a jpg or similar rather than a bmp.
Regards
Admin |
tom walker (Tomjwalker)
Member
Username: Tomjwalker
Post Number: 2
Registered: 9-2007
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| Posted on Monday, September 17, 2007 - 8:40 am: |
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Hi Admin,
Thanks for your response over the weekend!
Rgds,
Tom |
tom walker (Tomjwalker)
Member
Username: Tomjwalker
Post Number: 3
Registered: 9-2007
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| Posted on Wednesday, September 19, 2007 - 1:55 pm: |
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Hi Admin,
Can I use a 6v lead acid battery for the 5v logic supply on the MD22? If so, is the amp-hour rating important? If not, can you recommend an easy PORTABLE solution?
Thanks,
Tom |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 580
Registered: 10-2004
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| Posted on Wednesday, September 19, 2007 - 7:03 pm: |
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Hi Tom,
We do not have a published figure for a maximum logic supply but a freshly charged 6V SLA could be 7.35V so I would suggest this is too high. The logic supply only draws 50mA max so a NiCd or NiMH receiver pack would be better and lighter. We also stock battery holders so you could use individual NiMH cells. If you can advise the running time required, we will suggest some options.
Kind regards |
Dave in Winchester (Css_broadcast)
Member
Username: Css_broadcast
Post Number: 10
Registered: 4-2006
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| Posted on Wednesday, September 19, 2007 - 10:49 pm: |
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If size and weight isn't an issue with what you are trying to run, then a 6v SLA battery could be used but put it through a 5v regulator circuit. This way, you are max-capped at 5vdc until the battery obviously goes under voltage. As Admin states though, a MiMH or NiCad pack would be suitable. It just depends on what you currently have in your stock. Drawing 50mA wouldn't even need a heat sink, but to be safe, fit one anyway.
Current drain only applies to what the item you are using consumes. If it draws 100mA, then running a 100A battery will only be drained at the 100mA rate. Voltage is the critical issue. Logic boards must run at 5vdc and should use a completely smoothed supply. Sorry Admin, didn't mean to step on your toes. |
Dave in Winchester (Css_broadcast)
Member
Username: Css_broadcast
Post Number: 11
Registered: 4-2006
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| Posted on Wednesday, September 19, 2007 - 10:57 pm: |
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Forgot to add that in my opinion, using the 6vdc SLA battery would be better, going through a 5v regulator anyway. The reason is that the battery would supply high current longer than NiCads, therefore allowing 5vdc to supply the logic circuit for a longer duration. If you decide to change the 6vdc SLA battery to a 12vdc version, you MUST use that heat sink as you will be sinking 7vdc through the regulator alone, which will generate a lot of heat. The regulator may then drift. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 583
Registered: 10-2004
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| Posted on Thursday, September 20, 2007 - 2:31 pm: |
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Dave,
Thank you for your input - always most welcome. What I will add though is regarding your statement about SLA supplying a higher current longer than NiCd's. A term we use is Ah efficiency where the batteries effective Ah capacity varies with the load current. Most SLA's quote their Ah capacity based on a 20 hour discharge, draw more than 1/20 of the capacity (0.05C) figure and the Ah rating falls. A typical SLA at 3C would only last 7.5 minutes giving an Ah efficency at 3C of 37.5%. A Nicd or NiMh on the other hand can run at 3C and achieve an Ah efficiency of 70 to 90% and offers a higher power to weight ratio. So we consider on average use that NiMh and NiCd offer a higher current for longer that the equivalent Ah using SLA technology.
Just picking up on the need for a heatsink, good advice although technically if using a 7805 on a 12.7V SLA at the max logic current of 50mA, would dissipate 0.39W giving a temp rise of 25 Deg C above ambient which is well within its operating temperature range. In fact you could go up to maybe 150mA although it would be getting rather hot then but still within its operating limits.
Not trying to knock what you say but it is always good to have a healthy debate. |
Dave in Winchester (Css_broadcast)
Member
Username: Css_broadcast
Post Number: 12
Registered: 4-2006
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| Posted on Thursday, September 20, 2007 - 9:14 pm: |
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I'll just shut up then :oD
Being as NiCads and Nimhs are so superior, I wonder why alarm companies (security and fire) still use SLA's to power their panels and sensors for durations exceeding 8Hrs? I know NiCads are used in emergency lighting, so I wonder why not everything else?
I'm still trying to get my head around LiPO's at the moment, and thats bad enough. Still...you were right and I made an error. I will be shot at dawn for this mistake as I'm too tired for a healthy debate. You'd win anyway as it seems my technology knowledge is slightly out of date. Oh well, back to my Leclanché packs! I was wrong...I was wrong...I was wrong...! hehe |
tom walker (Tomjwalker)
Member
Username: Tomjwalker
Post Number: 4
Registered: 9-2007
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| Posted on Thursday, September 20, 2007 - 10:14 pm: |
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Hi Dave, Admin
Thank you both for your input!
I've decided on the NiCa/NiMh and guess a pack containing 4 x 1.2v should do?
Running time: 2 hours (max) between charging. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 584
Registered: 10-2004
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| Posted on Friday, September 21, 2007 - 3:58 pm: |
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Hi Dave, you know your input is always welcome.
SLA's are used in fire, intruder panels, UPS etc. due to their relative low cost and ease of charging. Fire panels have a low current drain thus using the SLA's in their optimum range. NiCads are used in lighting probably due to their physical size and weight + I'm not sure I would like SLA batteries leaking on my head.
Check out the new Lithium batteries from A123, could be the Lithium technology to take over from LiPo's etc.
Tom,
2 hours is nice and short, max load of 50mA gives 100mAh. You could start off with 1071-101 which is a charger complete with 4 off 1300mAh AA cells for £6.96 which will last all day. A battery holder 1063-033 for 21p and a battery lead 1063-100 for 13p and you're away. Just need to remember that the charger is a slow charger i.e. over night type but additional batteries cost £3.95 for a set of 4. |
tom walker (Tomjwalker)
Member
Username: Tomjwalker
Post Number: 5
Registered: 9-2007
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| Posted on Friday, September 21, 2007 - 5:07 pm: |
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Thanks Admin. Have a good w/e. |
