Battery simulator

Not a looker but it works well

Not a looker but it works well

A what ? A battery simulator.  I did not know they existed. I had made a lead accid battery charger (or more precise, something that turns a DC source in to charger that can stay 24/7 on the battery without cooking it. It switches over to float loading at a certain current level and starts loading if the battery voltage becomes to low.

But it had to be adjusted and in that case a lab supply is rather useless. A charging lead accid battery must be loaded with a fixed voltage. The battery’s own  voltage increases while current decreases. It is a voltage source, with an internal resistance that sinks current. Most powersupplies can not sink current and keep the voltage constant as long and as fast as possible.

There are supplies that can do this. They are named four quadrant power supplies. I have builed some active dummyloads in the past that can be used to sink current but they do not source a voltage to tell the charger what is going on.

There is not much info on the web about these things. Most I found were designed for li-ion or lipo batteries. These are much more delicate as a lead acid battery but with some small adaptions they can be scaled to lead acid use.

I added a pnp transistor between the 555 and the rest. I forgot to draw that in de schematic. betqween the base and the 555 output a 5k6 resistor. The emmiter to the 12V and the collector through a 270 ohm resistor to ground. And a 10k resistor from base to 12V



(I made a fault in the eagle schematic above, the base of Q3 is connected to the collector of Q1)

The design is based on an appnote from Maxim.


The ratsnest, most parts are smd

I used other opamps (TL072) and another shunt regulator. Besides that I had tpo scale it to 12V.



It has 2 modes of operation. The first is manual use. I have mounted 2 potmeters to adjust is very precise.  This way I can set it at the points I need for adjusting or testing a charger. For lithium based batteries this is even more important. You can set the voltage at 10V. The charger then thinks it is a very empty battery and allows a high current. You simulate the setpoint for voltage and current adjustments and the charger thinks it is a real battery.

The second mode is a sweep mode. It runs 1 time after by pressing the button or multiple times coupled to a pulse generator. The generator must give a 12V signal that goes down for a few ms every 6 seconds.  I added a 555 that is fixed at these settings. It will be better to use a potentiometer for the 555 periode time.

What it does is simple. It simulates a very hi speed  charging battery. So no more waiting on the charging and discharging of real batteries for tests

A simple charger

A simple charger

You see the voltage going up and the current going down. At the end you see the charger switching to float. In the manual mode you set the checkpoints, in autosweep you can sweep it.

A sick charger

A sick charger

This is a charger I used on a motorbike until it cooked the accu dry. The charger oscillates and only shows the yellow led instead of the red for bad, orange for almost empty. yellow in between  and green for full.

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