![]() ![]() My design requires the best energy use possible. Heat is annoying and a lost of energy in this case. The thread starts while I was thinking to add a coil to the design in the hope to raise effectiveness. Reading your ideas, searching the internet, thinking about the current design make me realised that my actual concept may not be the best way to go for my application. RE: PWM Circuit for AGM Battery Charger IRstuff (Aerospace) 8 Jan 15 20:17įirst thanks for all the comments, every thought is useful. I will correct the software to remove short pulse as suggested. Sorry if the schematic was not up to date with all the modifications I did during the test period, and I did not post the full schematics, the MCU is not relevant to the heat problem except for the PWM frequency. I wish I can find a diode with a lower drop voltage for D20, this should reduce the heat. I can easily raise the resistors power, but it's a bit more complicated to dissipate the heat produce by Q1 and D20.ĭ20 have been replace by a MBR2515L with 450mv drop voltage so it should dissipate around 7 watts at max power. The parts that heat a lot are the sense resistors, Q1 & D20 that are on the same heatsink. ![]() It's not a linear regulator that in fact have to drop 7 volts. I did implement a temperature sensor to control AGM charge.īattery temperature will stay low, they are surrounded by water not going over 10c.Ĭorrect me if I am wrong, but Q1 (IRF4905) has a 20mohm Rds, so at 15amp, it should drop around 0.3watt, not 105. I do not use UNO, the PWM is drive by an Atmel 89C5130 MCU. I did switch R8 from 100K to 1K but forget to correct the schematics. The 0-3.3V in relation with the sense resistor come from an ADM4073T. I design the circuit to handle 15 amps, but I limit the current to not more than 10amp via the PWM. The recommended bulk charge rate is around 10% of the battery capacity of 100amps so around 10amps. Hi, a few information's in regard to everyone post: RE: PWM Circuit for AGM Battery Charger OperaHouse (Electrical) 8 Jan 15 16:16 We ended up placing temperature indicating stickers on the battery systems on all our accounts and cautioned the customers about this, in that if the system were damaged, it would be at their expense. I've seen AGM thermal runaway happen 3 times at commercial customer sites, in one case destroying about $25,000 dollars of commercial batteries where the customer refused to replace their aging non compensated chargers with newer technology. AGMS as they get hotter start drawing more charging current for a given charger voltage and without remote battery temperature sensing by the charger, a thermal run away can happen. One last reason for this with AGMS is the possibility of battery thermal runaway if the batteries are in an uncontrolled temperature environment where battery temps can get up to 95 deg F or beyond. This aspect was always question number 1 when approaching the battery manufacturer for a warranty replacement.Īll the battery manufacturer's in my experience specify float versus temp for their AGM stationary batteries (measured on the positive terminal) to 2 significant digits and of course all modern commercial microprocessor controlled chargers have the selectable or customizable profiles in their design to match the battery manufacturers requirement. If off the curve, positive electrode corrosion tends to occur if off in the other direction, sulfation build up is likely. If resultant float is off in one direction, positive electrode (plays a more significant role in the gas recombination than the negative and, there is a heating effect and delta voltage effect on terminal voltage from the gas recombination itself). While batteries seem like simple devices, the chemistry of AGMs especially considering the gas recombination process is quite complex and demands the resultant float voltage to be correct for the battery temperature. And equally important for AGM batteries is to build into the charging circuit temperature compensation (preferably monitoring actual battery temperatures) to ensure the battery float voltage stays on the recommended curve.
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