Electric Vehicle Conversion Help - Distributed Charging System

Build Your Own Distributed Charging System

by Mark E. Hazen

A Distributed Charging System (DCS) can be made using many separate 12-V chargers paralleled with series-connected batteries as shown in the figure bellow. You can make this for less than or equal to the cost of a standard high-voltage bulk charger.

The chargers that you choose must be 'isolated' chargers. That means the output is isolated from the input. In other words, the output is floating. If they are not isolated chargers, they will short out when connected to the batteries.

An example of a possible charger selection is the Samlex 15-A charger (SEC-1215A). This charger is 3-stage and has a built-in ammeter. It is relatively small, priced very well and appears to be deigned well. It is most suitable for gel and AGM batteries but we recently learned that internal adjustments can be made to these to change the charging voltages for flooded batteries..

There has been some confusion over the Boost Voltage capability of these Samlex chargers. An earlier 2001-version manual states that an internal switch can be set to give a boost of 14.9 V. A later 2004 version manual states that the maximum boost setting is 14.4 V and shows dip switch settings on the rear of the charger. Apparently, Samlex made a design change to this charger without revising the model number to reflect the change. A boost voltage of 14.9 V (and higher) is essential to maintain the health of deep-cycle flooded lead-acid batteries, but would be damaging for gel and AGM type batteries. It's very possible that the company received many complaints from AGM owners who used the higher boost setting and ruined their batteries, thus the disappearance of the 14.9 V capability. That is just conjecture on my part.

Note that at the following Web page, Trojan recommends a daily charge voltage of 14.8 V and an equalization voltage of 15.5 V for heavy desulfation when needed. http://www.trojanbattery.com/BatteryMaintenance/Charging.aspx The 14.8 V (at 80^oC) for daily charge is intended to provide daily desulfation and acid mixing. Also note on this Web page Trojan's recommendations for VRLA batteries (gel and AGM). The recommended voltages for these battery types is much lower than for flooded lead acid.

Note: Keep in mind that the proper charge voltages depend on temperature. During hot summer months, boost, absorption and and end-of charge voltages do not need to be as high as in the cooler months and cold weather because the acid is more active and the chemical processes are more aggressive at higher temperatures. This is why temperature compensation is so important in a charger. In essence, the charger sets itself at the beginning of a charge session based on ambient temperature. Those chargers with a remote sensor that is attached to the side of a battery, can adjust voltages on the fly. If the battery starts to heat up (common in thermal runaway) the charger will cut the voltage back.

Other battery manufacturers and experts will recommend slightly different daily charge and equalization voltages and methods, but they all agree that a voltage greater than 14.4 is essential for the health of deep-cycle flooded lead-acid batteries. This higher voltage occurs during the last portion of the bulk charging stage (first stage or phase) and is called the boost voltage.

This charger is available from www.chargingchargers.com and from www.mrsolar.com. Ask for a quantity discount.

THIS JUST IN! (Aug. 15, 2010): A visitor to this site forwarded a document to me that is from Samlex. The document describes how to reset the SEC-1215A charger for higher voltages using internal adjustments. If you would like to use this procedure to adjust the settings in your chargers, download it here. Download SEC-1215A Settings Procedure

Charging solutions for both flooded and AGM battery technologies are made here in the USA under the Dual Pro brand. They offer single, dual, triple and quad chargers such as the PS3 triple charger shown here. Each charger has its own state-of-charge indicator display.

These chargers are microprocessor controlled, have the correct charging profile for long battery life and are temperature compensated. These chargers can be purchased from the following, and other, Web sites:

http://www.jmdualpro.com/index.php?main_page=index&cPath=3

In the diagram above, a digital voltmeter is added with a rotary selector switch to allow you to view the charging voltage and battery voltages when the charger is turned off.

Parts List: Go to the dealer site and enter the part number in the search box.

Digital Meter - www.digikey.com - part # CDPM606-ND or CDPM603-ND or CDPM632-ND or CDPM635-ND
5V Wall-plug Power Supply for the above meter, 150 mA or greater, any brand, add SPST switch on +5V wire.
Fuse Holder - www.digikey.com - part # F1488-ND - through-hole chassis mount
Power Switch - www.digikey.com - part # 360-2089-ND - 25A, 125VAC, DPDT or you can use a couple standard wall switches.
Power Indicator - www.mouser.com - part # 607-1050C1 - red neon, panel mount, 105 to 125 VAC
Rotary Switch - www.mouser.com - part # 690-C4D0212N-A - rotary, non-shorting, 2 pole, 12 position, 28V, 0.5A
Download the dial background for the knob. You will need a large knob to match the dial background. Click to download.

Umbilical Cord to Vehicle Connectors

For 10/12 batteries and 10/12 chargers: #12 multi-strand flexible wires

24-Pin Plug - www.galco.com - part # DMS3106A24-28P - 24 pins
24-Pin Socket - www.galco.com - part # DMS3102A24-28S - mate to above plug

Note that 2-phase AC is used in this example because there is just a little too much power being drawn for a single phase to be used. In this case, there are 12 chargers and the load is distributed evenly between 2 AC lines. If you have 8 or less chargers (15-A chargers), you can run all of them from a single AC line (20-A circuit).

This is a photo of my buddy Jim's system. It hangs on the wall in his garage next to his EV.

It looks bigger in this picture than it really is. See more pictures on Jim's blog

My homemade distributed charging system is shown below. Actually it was my prototype before selling the much improved commercial version. Each charger has its own battery voltage threshold detection circuit that changes the charge mode from Stage 1 Bulk to Stage 2 absorption. Each charger has a switch to manually place it in the Boost mode for desulfation when needed. You can just about see these switches mounted along the top and bottom of the cabinet. There is also a master switch (red-handled toggle, top right) that places all chargers in the Boost mode. Stage 1 lasts until the battery terminal voltage reaches 15.5V (adjustable) for each pair of 6V batteries. Stage 2 is presently set at a constant voltage of 14.4V (adjustable). I will soon decrease this voltage for the hot summer months.

Wiring and fusing to the batteries is shown below. A military-style 24-pin connector is used to connect the charger umbilical cord to the battery wiring. 30A fuses are used at the terminals of the batteries as a safety precaution in the event of a short along the lines somewhere or inside the charger. The fuses must be at the batteries because they are the largest energy sources.