Battery Management Systems
With all these open source projects... It seems the only two things we are missing are batteries and battery management... I'm not capable of initiating a conversation about planning open source DIY batteries, but I do believe that a BMS is important.
I am no expert on this subject, and much of what I think I know may be wrong. Please don't hesitate to interject and/or correct. The three types of BMS I know of are: 1) Passive and isolated, like a zener lamp. At a certain Voltage current is shunted to a resistor (a bulb in the example i read). Limits overcharging. 2) Passive but interactive. I can't remember the example of this very well, but it sat in between batteries and shunted current between the two batteries until they are equal in voltage. IIRC it was a passive device, not actively moving current. 3) Active. like Lee Hart's (BalancerLand - Intro) I see a couple ways of doing this. a) have a microprocessor watch voltage (and temp) of each battery and move current from the highest to the lowest etc. b) have a microprocessor watch voltage (and temp) of each battery as it charges and remove batteries from the string as they reach a defined voltage for that charging phase i) this would require a very smart charger or that the BMS work hand in hand with the charger. (you do have to reduce voltage when you remove a battery right? you can't charge a 24volt pack with 120 volts?) ii) technically this isn't BMS, but if you are charging a pack every night and every night it is equalized, it's darn close to BMS (until a battery goes bad). What I want out of a BMS: Effective inexpensive average joe can build it I would love for it to actively display individual voltage readings to a backlit dashmounted lcd, but I wouldn't pay an extra $100 for it. |
There was a guy at the Midwest Renewable Energy fair that had a home built charger that charged the bank of batteries then turned on a 12V charger that toped off each battery in the system, I've looked in to getting a pile of 6 or 12V chargers so I can charge each 6V battery so that it gets charged without having the affects of the other batteries in the string.
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Here are a few photos of the system Ryland just mentioned.
http://gallery.me.com/benhdvideoguy/...12456816880001 http://gallery.me.com/benhdvideoguy/...12456817260001 http://gallery.me.com/benhdvideoguy/...12456817570001 A logic board controls all those relays that route power to each battery individually to top it off. I seemed like a clever system. Also, my friend Tom, who is building the AC Dodge Neon, is planning on having a custom battery monitoring system. That is going to be a while before that's done, but it may actually become a product to be sold. If he goes open source with it, I will share the info here. |
If you are going to design something to turn on a trickle charger, why not include the trickle charger in the design and not buy a dozen of them?
Again, I am no expert, but when you bulk charge you keep the constant voltage and when you trickle charge (or top off if I am using the wrong term), don't you keep constant (and low) current? couldn't we do similar with PWM (since that is the fad)? |
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Here is one...
This is the one Im planning on using (dump controller) on my ev. Already using it for my solar panels. Works great. ghurd - Hurd Solar Renewable Energy | Dump Controllers Another similar setup but designed in tune for EV users like us. Volt Blocher And here for monitoring your batteries. http://www.evconvert.com/article/led...monitor-part-2 Hope this helps. |
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