Electronic Circuits and Projects Forum

No link available. The point is that they are 3 x 185AH inexpensive car batteries, now a car starter battery is designed to deliver a very high current for a short time period and then after a short rest (if car doesn't start) to quickly recover enough to supply a second short high current discharge. to start the engine.
True Deep cycle RE batteries (or golf cart batteries) have much thicker and less porous lead plates so will sustain a smaller discharge for a much longer time and to a higher depth of discharge, (typically 80% discharge instead of my 50%) They also cost 3 times more for the same capacity.

It may well be this quick recovery that I am seeing as a spike? However changing them out is not an option at present.

Hi again,


A theoretical power source has no resistance meaning you can load it to several million amps and the voltage wont crack even a millivolt. Real life sources unfortunately have internal resistance. They also have more than one theoretical capacitive element so the behavior is more complex then we usually have to think about in many applications. One of the unusual things is that they can recover after several minutes to some higher voltage level. Also, the internal resistance makes the voltage jump down when loaded and up when unloaded. These things can be a pain in the neck, but for your application what has to be done isnt that complicated. It might sound like it is, but to us guys that have studied these matters in great detail and worked in the field for many years in various capacities this is a piece of cake. Literally, this is not a hard thing to fix, so dont get too worried about what you have to do to fix it. It probably wont even be that expensive because most of the parts these days are rather cheap, even the higher powered MOSFETs for example. The most expensive thing would probably be the power resistors and a little metal enclosure to hold them safely, or possibly even some 12v light bulbs :chuckle: . Light bulbs however have other undesired characteristics unless you use one rated for much higher voltage, so power resistors would he the best bet assuming the caps dont work.

Lets take a quick look at the simplest solution since you say you dont need great accuracy.

A zener connected to a transistor and possibly a second more high power transistor operated in the linear mode. Since this only has to kick in when the voltage is too high, you want the zener to conduct at the upper voltage level. That turns the smaller transistor on part way and that turns the bigger transistor on part way. The result is the output is voltage regulated. This is your typical shunt regulator. Transistor needs a heat sink also, but a well sized load resistor will take some of the power out of the transistor allowing it to run cool while the resistor runs a bit hot. Add an op amp and you've got a control circuit. Disadvantage is not too good for accuracy when the temperature changes.

Second up is the same configuration, only instead of using a zener you actually build a shunt regulator. A simple one with a higher power transistor. This isnt that complicated either, and in our field the complexity on a scale from 0 to 100 is about 10. This means you will have to wire up one device that looks like a transistor (or a chip) and maybe two other transistors, a few resistors, a pot, and a small cap or two. This has the advantage of being easy to adjust and also quite stable.

What have you built in the past that was electronic and involved transistors?
Have you ever used an op amp?

Also, did you say that you know what resistance will load the bus down enough to prevent over voltage, or could you try a few experiments to find out some information about your system?

Hi again,


Oh ok, so you are dealing with some decent amount of power there then, and some significant current too.
Unfortunately, in order to suppress a voltage of 1.5v for 1/2 second at 42 amps (500Watt figure) you'd need about 14 Farads of capacitance. I dont think you'd want to do that, unless you get lucky and this figure is so nonlinear that a smaller capacitor actually does just enough, but that's something to test for.
So you'd be talking about some 0.2 to 0.3 ohms like you said, and at 500 watts that equals a good ATX power supply tester that can handle the power for at least a second or two, or whatever you need. You'd have to build a resistor bank if you wanted to do it any other way, perhaps using water cooled resistors.
Now that depends on how often this has to function, once per day, twice per day, etc. Resistors rated for 100 watts immersed in distilled water would handle the load pretty well, unless it had to work every two minutes :-)
If you could find 10 three ohm resistors each rated for 50 watts you'd probably have yourself a good resistor bank. I would suggest in this case switching each of the ten banks with their own power transistor.

Well if you havent worked with electronic parts for quite some time you might find this project a little bit of a challenge. You might want to try to get someone to build it for you. Unfortunately Florida is a bit far from me so a field trip down there would take too much time. It's too bad i'd really like to see your setup first hand. Maybe you can take some nice hi res photos and post them so we can see exactly what we are dealing with.

If the caps don't work I will try the water heater route. Surely activating a 10 watt coil must be straight forward ? I HOPE!! LOL.

PS for the second day the inverters did not trip; Very Strange