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April 1, 2008
about 7 years ago
Hi, I’m been using the battery packages for almost a year now without any problem. I have also been using other LiPo packages for almost 10 years, all without any protection circuit. Use a good charger according to LiPo specifications and don’t overload the battery and you will be safe. Never go under 2.75 volts when discharging and you won’t have any problem. For further reading read my lab report
about 8 years ago
Perhaps a simple solution would be three zener diodes (200 + 200 + 100) volts and a resistor. For example 1N5956BRLGOSTR-ND and 1N5271B-TPTR-ND. Price for the zener diodes is just 20 cents. Then change the RC net, now that the HV supply is correct, and off you go.
I have not tested this solution above but it seems reasonable. Instead I did an adjustable (300 - 1800 v) regulated HV supply to be able to verify the characteristic curve of the GM tube (count rate vs. HV).
The main concern is that the +1500 volt is a factor three over the specification of the tube. In a longer run there is a probability that this will damage the tube. The very heavy total ionization of the gas, due to the high electrostatic field, will lead to an avalanche that in this case can lead to outgassing from the tube materials into the active gas. This in turn will lead to an unwanted ageing effect. This will manifest themselves as protrusions or films (called whiskers'). The practical long term effect is loss of gain, stretched pulses and eventually completely electrical breakdown.
Another effect you can see is pileup, you have to turn of the high voltage, turn it on again, to get the tube to start counting events again.
Some serious design issues of Sparkfun Geiger Counter
“Waking the sleeping Bear”
First of all I’m a big fan of Sparkfun. I really admire their innovative products, good prices, fast shipments and customer support. I’m a returning customer and will keep on being that.
However when you see a mistake it’s fair to do an alert about that so the slip can be rectified. The Geiger Counter, SKU: SEN-09848 has some serious issues.
Even if Sparkfun clearly has notified that this is a product for educational purposes many people, myself included, have the intention to use is for more serious use. Taken into account the recently mishap in Fukushima and the fact that I’m living close to a nuclear plant, I wanted the device to give me some feedback if a situation would arise.
There are three issues with the Sparkfun Geiger Muller Counter (GMC for short). Two are more serious issues and the third is more annoying.
• Incorrect High Voltage
• Badly design of detection circuit
• Bad placement of the GM tube.
The High Voltage is about 1550 volts if correctly measured. To correctly measure the voltage you will need a voltage meter with at least 1 G Ohms (1E9 Ohms). This is the voltage a zero count rate. The voltage will drop to about 1050 volts a high count rates (> 300 CPS). The GM tube has a recommended operating point of 500 volts and the operating range is specified to in the interval 450 – 650 volts. Operating at 1500 volts will give avalanche and secondary effects and can produces a total ionization of the gas between the electrodes. You can even reach a self-sustaining discharge that will continue as long as the voltage is applied by a single detection event. This region shall be avoided due to that operation here can/will degrade the tube in a longer perspective. Also, the pulse counting will be more or less random and not represent the true counting rate.
Due to the HV problem, the designer, not realizing this, had to put in a “heavy” RC filter to compensate for the error in the HV design. The RC filter (R10/C9) gives a time constant of about 8 mille seconds. This in turn limits the maximum count frequency to about 60 pulses per seconds. The actual GM tube can perform much better than that. Typically an event gives a 100uS pulse. You can actually see the avalanche effects (due to running far over tube specification) in the oscilloscope picture in the tutorial on the GMC web page.
Normally a radiation event should give a pulse like this:
When the HV is far too high you will get something like this due to avalanche effects etc:
Compare the later picture with the one in the Sparkfun tutorial!
With correct HV and detector circuit the GM tube will be able to count thousands of pulses per second. This needs to be redesign.
Bad Placement of GM tube!
In the original design of the PCB board it was easy to remove the protection cap of the tube (when you want to do Alfa measurements). Se picture in the tutorial. In the production design the placement of the GM tube was changed. Now it’s very difficult to remove the cap without jeopardizing the extremely sensitive mica front window of the tube. I did this mistake and “puff” the GM tube was destroyed.
It should be a rather simple task for Sparkfun to assemble some instructions and components to upgrade the device fixing the two more serious points above.
Member #115862 in the product thread was on the right track concerning this issue. He also had some point on how to fix the HV problem.
For a more complete report follow the links below:
about 8 years ago
I did some modifications and tests to this battery pack. If you really want to use all the "juice" you must do two modifications of the battery pack.
A) Remove the protection circuit;
B) Change the cables to a bigger area. My load test gave a discharge curve that confirmed the capacity of the battery’s 6000 mAh. At about 1 C you could have a load for about 1 hour and 12 minutes.
If you want the details follow this link:
This is a good battery pack!
SM6FIE, Bo Gardmark
about 8 years ago
Removed by user, wrong product, sorry...
about 8 years ago
Have same problem, can't see drawing, Access Deinied...
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