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Forum Index : Microcontroller and PC projects : OK SO JUST thAT EVERY ONE knows
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sparkey Senior Member  Joined: 15/06/2011 Location: AustraliaPosts: 819 |
what i am attemptin to do with my"maxi" log data as volts from six batterys "given i am running a 36 volt system" 6 times 225 ah trojan t105 plus batterys in series //ok now i have sent and paid for a maxi from "hamfield" today i can run a loom to the batterys since the dc path only reaches about 4-5 meters ok ..um some may be fimialar with the "ETI326 kit" exp scale volt meter i had built six of them from scratch ..and wasrunning them in bar mode to "assatain every battery voltage ..now given that fact it was draining the batterys only by a little but still a drain...i want to be able to read every battery on the screen in a little graph or even a line out with its voltage ..aside from that i also want too read current comming in from my panels which is prolly to high "40 volts" for the maxi to cope with ok... well today i ordered a maxi and io card expander from hamfield...and paid for it as well ..dont know if i have thrown away 160 bucks there .. but if it does arrive i will be happy to be able to get it built...so that is basically what i want ..from the maxi aside from a pulse generator but i have got that in the works my self ... thanks to all on the web for even trying to under stand me and thanks to those who may have any ideas on this topic..regards sparkey.... technicians do it with least resistance |
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| rhamer Senior Member Joined: 06/06/2011 Location: AustraliaPosts: 174 |
May I ask why you think you could have thrown away $160 and why it might not arive. Was there some part of the order process that did not appear correct? I have had many orders from others without any complaints and I am concerned when someone appears to be unhappy about some part of the process. Please email me at maxexp@hamfield.com.au and I will try and sort out any issues you may have. Regards Rohan Rohan Hamer HAMFIELD Software & Hardware Solutions Makers of the Maximite Expander. http://www.hamfield.com.au |
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powerednut Senior Member Joined: 09/12/2009 Location: AustraliaPosts: 221 |
Hi Sparkey, I havn't looked in any detail at the Maxi but the microcontroller appears to be running at 5V, and you shouldn't hook anything up to its input ports that could have a higher voltage than that. That may sound like you've wasted your money, but you havn't. All you need to do is scale your input voltages to something the microcontroller can handle. The easiest way to do this for voltages that may be higher than +5V is to use 2 resistors in series to form a voltage divider. For 48V max input (whats the peak output from your panels?) I'd use an 18k connected to the panel +V connected to a 2k resistor connected to gnd. This resistor ratio will give you 1/10th the input voltage at the junction between the two resistors - use this as the input to your maxi. That way if your panel voltage is 48V you'll have 4.8V on your maxi's input pin. This to note: - Build some calibration code into your program - all resistors have errors and that will effect the voltage. Calibration code will allow you to correct for this. - Make sure you have a good margin for error between the maximum voltage of your input and the +5V the maxi can handle without smoking itself. To be honest the 2V margin on my suggestion above would make me nervous, however if your max voltage is actually 40V then it'd be plenty. I don't know squat about the maximites - take my guesses about the +5V input with a grain of salt and look it up for yourself. it may be 3.3V or something |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
thamk you regards sparkey technicians do it with least resistance |
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| RossW Guru  Joined: 25/02/2006 Location: AustraliaPosts: 495 |
Just an addendum to this. While a 1:10 divider may appear "the fix", you need to do the calculations. A 48V bank will float at 54+ volts, so you may need even higher divider. The problem with that is that the further you divide, the less your resolution becomes. If you have a 10-bit ADC, you have only 1024 discrete steps, and thats assuming no jitter. So a 0-60V input means your *theoretical* best resolution is 0.06V Enough for some, but by the time you take realistic conditions into account, you'll be hard pressed to make better than 0.1V readings. Barely good enough for decent battery control. An opamp level shifter is probably unnecessarily complex for you, but a simple and cheap way would be to "wash off" some of your volts with a zener, or some zener diodes. For example, if you got 3, 12V zeners in series you'll lose 36V right there. You now have a battery input from (say) 40 to 60V, with an output after the zener of 4 to 24V. A span of only 20V. You still need a divider, but now a 4:1 divider will suffice, and you get resolution closer to 0.02V per bit. Much more useful. |
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| powerednut Senior Member Joined: 09/12/2009 Location: AustraliaPosts: 221 |
thanks rossw - good info. |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
um i left school in 1983 after finishing i got a job with:ritronics "some of you will know who i am talking about started as sales assist within a couple of months took over the job as head of the kit dept only job ive ever really enjoyed doing i rember:cpm" the bigb one and two ...i was also head storeman at the same time if we had it i knew where to find it ///after this went to microfusion and was assybly terminals and xt turbos for schools and hospitals then went to many repair service jobs ..as i say "build it and they will come ///regards sparkey technicians do it with least resistance |
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