Hello,
I have brought the BM200 NiMH charger to market in it’s new form with firmware that can test and charge C and D cells as well as AA and AAA cells. This thread is to post any questions about the charger.
To get things started, below are thermal images of four chargers that I just did a charge test on, including the BM200. In order from bottom left PowerEx C9000, bottom right BM200, top left La Crosse BC-1000, and top right AccuPower IQ328.
The charge test was started at the first image, time indicated. All chargers set to charge at 1000 mA on all four channels. The batteries are new PowerEx AA 2700 cells. The cells were completely discharge and cooled before the charge test.
It is interesting to note that the BC-1000 thermal cycled twice during the charge test and the IQ328 once. You can see them cool down in some images. Those chargers thermal cycle by shutting down all four charge channels. You can also note that the BM200 thermal cycled on only one channel during the test. Even though the BM200 charger body appears hotter that heat is not getting into the batteries to cause thermal shutdown. In all the chargers the hot spots are the charger case, the batteries appear cooler. This is normal as good cells do not generate heat early in the charge cycle. They will only start generating heat once full charge is reached, then the excess charge current is turned into heat. That is the time the charger should be detecting -dV and terminating charge.
As you can see the C9000 is just the best, again. No thermal cycles, just charges batteries with moderate heat generation.
You are right that thermals are not as good as desired. That is why a complete design review is underway to improve that.
However the temps on the cells remain in range, there is more room for cooling air on the BM200 unlike the chargers that thermal cycle during the same charge test. In the BC-1000 and the IQ328 the cells got hot enough to trip the thermal limit, the BC-1000 twice during the charge. Even though in the thermal images they appear cooler more heat is being conducted into the batteries and they trip thermal limit. The BM200 has almost as much room for cooling as the C9000. Good cooling air space is the thing keeping the BM200 cells in acceptable range. That is also one reason it looks hotter, you see much more of the charger body that is not shadowed by the batteries. On the BC-1000 and IQ328 the cells are so close they shadow the heat form the charger body. I will try to get some closeup images so the cell temps are more obvious and not washed out by nearby heat.
Having said all that it obviously needs improvement. But so do the other chargers, they trip thermal limits repeatedly, except the C9000.
Here is an example of the shadow of the batteries on the BC-1000. So in the top down shot the batteries shadow the heat under them. Also note the hot spots on the negative metal contacts conducting heat into the batteries. This image was taken about 30 min after starting charge on 4 cells at 1000 mA. It thermal cycled about 30 minutes later. I will have an image of BM200 and some others in same condition soon.
kreisler,
Thanks for the comment. Of course right now the C9000 is better. I am bringing a new product to market. Unfortunately the first hack is not as good as desired. It will improve. Right now it is satisfactory and easier to use, much better user interface, and has some added features such as internal resistance measurement and the ability to charge and test C and D cells out of the box. If you have used the charger and see features you would like included post that information here or contact me directly. It will be reviewed and considered for inclusion.
I guess that is the one thing I want to say to everyone. Your input counts. I tried for years to talk to the other manufacturers about products. Most would not give me the time of day. Now I have that opportunity to make changes, to make a product better. I want to include you all in that process. That is one thing this thread is about.
I know the thermal performance is not great. However it is as good now as most other chargers. Not good enough, it will be improved. We are working on it. If you have other ideas post them here.
Thanks,
Oh, and I like to play with my thermal camera. If you want images of something let me know, I will try to get it.
Nice work Danaco and welcome to the forum, good to see proper testing and design revisions. What other testing do you plan to do?
Do you have any more info on the charger? Can we see an ordinary photo comparing the chargers? Will it use a 12vdc input? What sort of price range? Where will it be available for purchase?
Kriesler will nearly always delete posts causing confusion. If you quote his post when answering he can do what ever pleases him and we know whats going on.
By the way, welcome and thanks for the testing. Enjoy your stay.
As we speak testing is being done on design changes to the charging circuit. Once a pilot production is done I will have units for testing and post the results here. Some other nice to have changes have been made as well such as changing the default charging current to 400 mA instead of 200 mA. A much more useful setting.
Some picture below. The charger is available on web site danaco.net and on ebay. It does use 12V input (2 Amps needed for maximum charge current) and can work with suitable car adapter for portable use or even with a solar panel in the field.
Here are the BM200 images I promised. Same conditions as the BC-1000. Charge 4 cells at 1000 mA started about 30 minutes before.
Note that the side view shows the hot charger body but there is plenty of room between the charger body and the cells for cooling air. Therefore less heat is transferred to the cells under charge. The cells are actually much cooler than the charger body below.
The top view is even more dramatic. You can see the relatively cool cells and the hot charger body below. Cooling air from convection is keeping the outside two cells cooler than the inside two cells.
Also note that ambient conditions are actually warmer than the BC-1000 shots as well.
This version of the BM200 is produced by Opus Instruments. However it has been changed. The firmware has been changed in order to charge and test C and D cells. It can charge and test up to 20 Ah cells. Also the charging circuit has been modified to improve thermal performance. Performance is still not as good as desired, however it is as good as or better than many chargers on the market. And it is being improved. I continue to work with the engineers at Opus to improve this design. Other chargers have gone through their issues, does anyone remember the La Crosse BC-900/BC-9009 meltdown issue, and not come out the other side much better. I am committed to improvement on this charger.
Hi Jeansy,
Full charge event is -dV like all NiMH chargers. There is a secondary 0dV condition that is checked as well. Depending on either one of those the full condition is set. The 0dV is a backup event, the -dV condition is primary for full charge termination.
I have never seen it miss the termination point on good quality cells, or any cells I tested for that matter. I have tested at all available rates from 200 to 1400 mA. Of course the concern is that at lower rates of charge it is harder for the charger to detect the -dV condition. This charger seems to be very good at determining that event. I suspect the addition of the 0dV algorithm backup may help with that. I have not gotten any reports from testers or customers about the charger missing charge termination. That does not mean it has not happened since not everyone would communicate that to me.
Hope that answered your question.
There are some other conditions that will terminate charge as well which are being added to the new model. They are backup events in case of defective cells or other abnormal conditions. However those are not in the current shipping charger. They will be in the new model. I should have some of those pre-production units for testing within the next week or two.
