Interesting Mark, If I remember correctly your chargers are higher current than the 350ma and 1A chargers I will be making?
I have had 350ma on a pack for over 2 days with 12V fan running, with only a 3-4 degree temp rise above ambient.
The pack was in thermal zone at over 170 for the last half day of that test.
They are using the 350mA Meanwell LED supplies, but I run 2 sets, one for each pack, and spillover is allowed through the 12 ohm balancing resistor connecting the two packs. In the car the temps seem to rise faster, and once you add a closed car and sunlight the temps go into runaway within a few hours. In the winter this isn't an issue.
Thanks for the details Mark, and It was nice to speak with you yesterday.
I duplicated your PTC temp to resistance test in water with a single strip, and got very similar results to your test. http://99mpg.com/Data/resources/down...sistance-2.pdf
I ran a 100ma CC through the strip, and measured the resultant voltage.
I tested the strip in air at 200maCC and did not see any self heating, so at 100ma I was reading true ohms with 3 decimal places of accuracy.
It looks like the PTC is pretty linear until it gets in the 135 degree area, then it changes rapidly. Great for detecting a hot area or cell in the pack, but not much good as an accurate pack temp sensor for the temps over 125-130.
At 145 F, the resistance continued to rise until the sensor basically open circuited.
Can I suggest use the programmer I have recommended for the BCM gauge as quite a few people already have that, and are likely to be interested in the charger. 5 sil pins are all that is reqd for the connections. It can burn the standard microchip hex files to 5v devices.
It's cheaper and easier to use than the full micriochip thingy as well IMO.
I have 2 programmers already,and am not interested in getting another, so I will go with what I have. Since we are programming the same PIC devices with the same programming pins, I expect that either programmer will work.
I can provide both types of connectors so either programmer can be used.
Thanks for doing the test. It looks fairly exponential throughout its range, and I see that reading twelve cells at once via a PTC isn't as straighforward as other documents here have indicated. E.g. 12 cells at 120°F would have the same reading as 11 cold cells plus one at 150°F. You couldn't hide a cell at 155°F, though. Interesting.
Also, it would be interesting to see if it reaches 600 ohms at 160F as that is the key performance # that I've been told.
Quote:
Originally Posted by Mike Dabrowski 2000
Thanks for the details Mark, and It was nice to speak with you yesterday.
I duplicated your PTC temp to resistance test in water with a single strip, and got very similar results to your test. http://99mpg.com/Data/resources/down...sistance-2.pdf
I ran a 100ma CC through the strip, and measured the resultant voltage.
I tested the strip in air at 200maCC and did not see any self heating, so at 100ma I was reading true ohms with 3 decimal places of accuracy.
It looks like the PTC is pretty linear until it gets in the 135 degree area, then it changes rapidly. Great for detecting a hot area or cell in the pack, but not much good as an accurate pack temp sensor for the temps over 125-130.
At 145 F, the resistance continued to rise until the sensor basically open circuited.
From the PTC Strips thread I started in 2008, here is an original quote:
I did this test by putting a single ptc strip in a pot of water on the stove with the PTC ends sticking out from under a glass lid. The temp probe was in the water and updated every 30 secs. I recorded until the temp probe maxed out. The strip's resistance climbed exponentially and was well over 20k ohms when I pulled it out; the water hadn't even started boiling.
My test could have been much better controlled, so yours may be more accurate.
I have a lab hotplate with magnetic stirrer, so I placed a ceramic dish that was about 3" tall X 5" diameter on the hotplate. I bent a full length PTC strip between each ptc sensor so the strip made a loop about 4" diameter I put a right angle bend on the ends so the bare metal was above the water surface. Connections with mini hook test leads.
The stirrer kept the water pretty uniform until I got to 120 or so, and then the temp shot up quickly as the heat finally soaked through the ceramic.
A better test would be to datalog the temp and resistance as the container warms at a more uniform and controlled way.
I was mainly trying to decide if I can use the PTC resistance to do double duty for temperature measurement, and hot cell detection.
Probably not.
The other 4 temperatures sensors may be a better place to start?
I will look at tapping one or more of those or possibily just add a MIMA type temperature probe that would measure the pack exhaust air to the design.
It would be great if the BCM could be powered up so peters BCM monitor could give the charger the pack information, but that has not been accomplished without codes if I remember correctly.
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