Hacking the Schumacher SPEEDCHARGER for PHEV & EV use

    If you find any of this information useful please leave a comment.

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.


12 Responses to “Hacking the Schumacher SPEEDCHARGER for PHEV & EV use”

  1. Louis Ruffino Says:

    Very good work.

    I have some A123 batteries for which I am trying to build a charger. Your work is very helpful.

  2. Steve Powers Says:

    I use these to charge my EV (actually, 11 of them, 1 per battery) – Do you know how to hack them so that they automatically start up at the 6 A rate so I don’t have to set each one individually every time I go to charge? I want the highest rate possible, but I still want the safety features and maintain mode to keep working. Any ideas? Thanks, Steve Powers – Atlanta

  3. Thanks for posting this information. I would like to use the SC-600A to charge my AGM battery however the manufacturer has very specific charging instructions with respect to voltage. The battery is partially charged 11.2V, when I connect it to the charger it dispays 75% which seems high and then begins to charge. Should be OK right, well the voltage is very low, 12.9V and the current is also low 0.6A dropping to 0.5A over 30 min. The recommended voltage is 14.4V bulk and absorption and 13.5V for trickle. I am using a cheap DVOM, so I would not be able to observe discrete pulses of 14V. The pulse strategy would also mess up the current measurement. I was planing to return the charger because of the low voltage condition but based on your write up maybe it is a measurement error. QUESTION: Have you observed the voltage (amplitude) of these pulses, and if so are they between 14V and 15V in absorption and 13.5V in trickle? Thanks again!

  4. Tim Powell Says:

    I have been pondering various schemes for an AFFORDABLE smart charger for a 22x12V AGM pack. My best idea so far is based on monitoring current, voltage, and temperature and electromechanically modulating a high power variac.

    I have considered various standalone PLCs and microcontrollers as the brain and I/O but am currently favoring a laptop and a USB I/O device (e.g. Measurement Computing MiniLAB 1008) due to cost of PLCs, lack of experience with micros, and competence with Visual Basic.

    Your solution seems far better, but I lack the necessary knowledge to ececute it. I would be EXTREMELY interested in additional specific information/schematics on how you did it! There are alot of “check back later” type entries in your post. Rest assured that I will.

  5. Dave Delman Says:

    …and I am using 13 of the SC2500A chargers. I’d love to figure out how to make 25 amps and AGM battery type as the default when turned on.

  6. Mine just quit and a diode looks burnt. The problem is the #’s are not readable. If you look at your pic of the board that contains the transformer there is a vertical resistor underneath it.(large gray). Just to the left of that resistor is a diode. Could you tell me the #’s on that diode ? It would be greatly appreciated !

    Thanks !

  7. john hostetter Says:

    My thoughts, this is ideal for a 36 v golf cart charger. I got three units but had trouble chaseing the circuit due to poor eyesight. One unit should work with circuit modification, ie transformer cange but it would help to see the start
    circuit to be certain. Thanks for the info…

  8. Tom Jennings Says:

    I found you information interesting. Could you possibly help me, or direct me to someone who can. I have the Schumacher Speedcharger SC-600A and it stopped delivering DC voltage for charging. I took it appart and it appeared the NTX2995 transistor had been fried. I replaced it, put it all back together and still no dc output. Any idea of where to go next. My newphew is good with electronics but told me I needed a schematic for him to help me troubleshoot and repair the problem. Thanks for your time.

    • Facebook took over as my Social Network and I let this BLOG fall way behind. I’m back scanning some 500+ comments. I’ll see what I can do.

  9. Norman Halfacre Says:

    I hope you are still posting information about your projects. I really enjoyed this one. I was looking for some information about the SC-600A battery charger when your website came up. I have two of these SC-600A chargers that I use for my golf cart batteries and up to now they have worked pretty well. Unfortunately both of them went bad. The power transistor (I believe you said they was a power mosfet) mounted on the heatsink near the high voltage section shorted. It has a burned spot on the circuit board underneath the heatsink going over to the one watt resistor, I believe is a one watt .43 ohm. Probably a moisture problem. The other one had a shorted MBR1545 diode that I replaced and that fixed it. I purchased two of the diodes on ebay for under five dollars shipped. If you have any information about a replacement transistor, part number, or where I can get something to replace the power mosfet, I would very much appreciate the help. The Schumacher company absolutely will not give out any information at all. They said these units are not repairable since they are automatically controlled by a microprocessor. I never saw a microprocessor inside the charger, only the ap3845 pwm controller that you mentioned in your circuit description. I replaced the MBR1545 diode on the other unit, so I know they can be repaired if parts are available. Thank you and keep up the good work.

  10. Rob Swenson Says:

    I also own one, in which last night it starts to emit a high pitched constantly naggin noise. Tried to recharge failed with two dialectic tones of inscrutable horror. Bad Idea… ANYHOW ARE THEY SUPPOSED TO EMIT SOUNDS??? I didn’t even recall that being the case. Any thoughts?

    • The cheap-ass little fans are made in china and they are bronze bushings that run dry on oil. When the fan quits the power supply overheats and blows out he MOSFET driver. The noise is the fan dieing. Both my 6A and 12A blew out from overheat after the fans quit.

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