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My project for the past few weeks has been hacking into a nifty little battery charger manufactured by Schumacher called the “SPEEDCHARGER” model SC-600A. A fellow EVer told me about this AGM charger he bought from Wal-Mart. Now the last place I would look for a charger for AGM batteries was at Wal-Mart. I bought one and when I got home I tore it all apart. Later in this report I will explain its operation in great detail. I was excited to find a simple 3-stage battery charger in such a small package, all the logic was on a 3 inch square PC Board. What I have done is created a 320VDC supply using the MPU in this little charger to control the power into a 20 battery (12V each) PHEV Prius pack. It would also be easy enough to modify it to work with any number of 12 volt batteries up to 20, like 12 for a 144VDC EV pack or 10 for a 120VDC EV pack.
Here is the PIC controller LED board, this is the brain of the charger. All I had to do is come up with a voltage divider that divides the 20 battery pack by 20 and feed this voltage into the control line. (It’s a bit more complicated than that but simply put.)
Here is my “Bread Board”, yes, literally mounted on a piece of shelf board. I hacked up an old 200 watt AT power supply, stripping out all the LV components leaving just the HV capacitors, rectifiers & chokes. The old AT power supplies used 320VDC, the way they got this was on 115V it used a voltage doubler, on 230V it just fed the bridge rectifier across the two series connected high voltage capacitors.
The SC-600A has settings for 6 volt or 12 volt as well as 2amp, 4amp and 6amp. It’s kind of neat how they control the current as there is no current shunt in this unit as they don’t measure the current, they caculate it from the Pulse Width Modulation (PWM). I’ll detail this later on.
Here is the finished Version 1.01 PHEV 260VDC battery charger. I mounted the original right onto the old AT power supply. Not bad for less than $50 for a 800 watt charger. Version 2.0 will use a 450 watt ATX supply with the hope of a bit more power.
STOCK SC-600A – Theory of Operation (Check back later!)
Voltage Doubler – How it Works (soon!)
EV Modified SC-600A – Modification & Theory of Operation (Check back later!)
Interface Circuit Board Schematic (Check Back Later!)
Terminology Used in this article (In Progress!)
[The Power Brick] – The Constant Current power supply used in the SC-600A, it measures 5.5″ x 3.5″ in size and mounts in the bottom of the case. This unit has two separate sections as do most switch-mode power supplies. The HV side has a power MOSFET controlled by the AP3845CP current mode PWM integrated circuit and a 14V house-keeping power supply. The LV section has the 6AMP @ 15.5V output and a 14V house-keeping supply as well. There is a 6V 3-terminal regulator that supplies power to the MPU PCB. There also is a power resistor/12V zenerdiode supply for the 12V 1.5″ case cooling fan. One odd thing about this is as the load on the output changes so does the speed of the fan, the zener just caps the voltage at 12V. This unit is either ON providing about 6 amps of current or OFF. The way they get 2 amps & 4 amps is the MPU PCB itself uses PWM through an opto-isolator that turns the power brick ON and OFF. By controlled ON/OFF the unit can effectually provide 2 amps or 4 amps of current into the battery. In the 6 amp mode the MPU PCB just holds the power brick ON. This all happens until the MPU CPU needs to switch into Constant Voltage Mode when it uses PWM to hold the voltage constant. Think of it as “pulsing” a PWM power supply On & Off to maintain a constant voltage. There is a relay on this board that is controlled by the MPU PCB, the reason for this is two fold, the MPU PCB checks for proper connection (6V or 12V battery) and correct polarity before sending power out to the cable clamps. This also prevents “sparking” of the clips while connecting them igniting nearby hydrogen gas causing an explosion resulting in sulfuric acid rain on all nearby persons.
[The MPU PCB] – The brains of this charger uses a simple PIC chip programmed to charge AGM type batteries. The algorithm used seems to favor the AGM as there is no selection button as on the “Big Brother” Schumaker SC-1200A model. I don’t see a problem charging flooded batteries using AGM algorithms, they still will charge up fine just a bit slower. You will destroy an AGM battery if you charge it like a flooded battery. There are only 5 wires connecting this to the Power Brick, Ground, +6V IN, relay control OUT, Battery Voltage Sense IN and Power Brick ON/OFF (PWM). (to be continued…)
[Chip Bag Clips] – Recycle everything, use them to hold chip bags closed. You don’t want up to 320VDC dangling on these so they get replaced with a 50A Anderson Power Connector.