I'm building a battery charger that can charge multiple batteries at a time, and I'm currently looking at Linear Tech's LTC4011 IC, but I think it can only change once battery at a time (a single battery containing up to 16 cells, as I understand it). Are there any ICs that can charge multiple batteries simultaneously yet separately? (Also, how might an IC such as the LTC4011 react to charging multiple batteries that are placed in series, "pretending" to be one big battery?) I imagine the chemical charging profile would be all messed up if the individual batteries aren't all at the same charge when plugged in)
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\$\begingroup\$ You are correct in your thinking. You don't want to mix batteries with various states of charge on one series charging loop. You have to use separate chargers per set of batteries. If a set of cells is always wired up in a pack and always charges/discharges together, then you can charge them all at once from a single battery charger. Otherwise, never mix and match batteries into one series charger. \$\endgroup\$– hortaCommented Jan 11, 2017 at 22:14
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3 Answers
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From the LTC4011 datasheet:
Based on this, I think that the charger IC determines the average single-cell voltage input and uses that as a basis for how much current to charge with. So if you have a dead battery and a 100% battery connected in series, it would detect 50% voltage and charge at a normal rate, therefore damaging your fully charged battery.
Further it states in the datasheet at the bottom of page 22 that "charging parallel cells is not recommended". So it appears this IC was designed with only one battery pack in mind. If you are looking for something that will charge multiple batteries separately, you might have to use a multi-port charger from HobbyKing or something, those will typically run you > $50 USD based on what I have seen searching the website.
answered Jan 11, 2017 at 22:01
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\$\begingroup\$ Thanks for the feedback - definitely helpful! I can't tag it as an answer because it technically doesn't answer the question I posted (about whether there are IC that can charge multiple cells). However, it DOES answer an underlying question I've been trying to find the answer to, which is whether charging multiple battery packs could cause damage. Much appreciated! \$\endgroup\$ Commented Jan 12, 2017 at 13:54
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I have never seen such an IC. I do not think it exists. I believe that the chargers which have this functionality (independent charging of multiple cells) use a specialized microcontroller to monitor all the cells.
If you do this, you may also consider including temperature sensing, although this is not necessarily required. It would allow you the option of doing dT/dt charge termination.
It really is much better to charge each cell individually compared to charging in series pairs as many NiMH chargers do.
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The charger shouldn't see a difference between multiple series cells regardless if they are individual cells or battery packs. NiMH batteries are just raw cells. As long as the voltage limits are observed it should work the same. A charger IC that can do a 9.6V battery could do 8 series cells, but can't do 9.
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\$\begingroup\$ But if, say, I connect a fully DIScharged battery pack with a fully charged battery pack, would that mess up the charging reaction in either/both batteries? This is what I meant about the chemical charging profile in my question, and it's my main concern about trying this. \$\endgroup\$ Commented Jan 11, 2017 at 20:20