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[on:]

One 12v car battery powers 2 loads. One load is 3.5A and the other is 100mA. The 100mA load is always on and when the 3.5A load gets switched on, scope readings show the amp draw momentarily dropping to half or less and voltage dropping from 12v to about 9.5v on the 100mA load. How can I maintain steady, smooth voltage and current to the low amp load during the brief time that the much larger load is energized? Would I need to use a large inductor or large cap to help momentarily sustain the 100mA current and voltage during this time?

[Reply #1 on:]

This circuit may be what you need:

[Reply #2 on:]

That sounds like a very discharged or sick car battery. A 3.5 amp load for a car battery should not cause a noticeable voltage drop.

Lety

[Reply #3 on:]

A better description of the loads and how they are connected will help.

We can all assume they are nice resistor loads, but if you've got some large reactive values in there then all sorts of strange things can happen during transient conditions.

[Reply #4 on:]

It's super simple. Just a car battery, a switch, a 3.5A power lock actuator, and a analog camera. That's it. The switch activates the power door lock actuator.

[Reply #5 on:]

It's super simple. Just a car battery, a switch, a 3.5A power lock actuator, and a analog camera. That's it. The switch activates the power door lock actuator.

Don't forget to remind them that the ground wire for all this is a single conductor of a cat5 cable. sad.

[Reply #6 on:]

It's super simple. Just a car battery, a switch, a 3.5A power lock actuator, and a analog camera. That's it. The switch activates the power door lock actuator.

Don't forget to remind them that the ground wire for all this is a single conductor of a cat5 cable. sad.

it's irrelevant. I've tried a much shorter 18GA wire in place of it. Of course, I still get the same result because it's unrelated to the problem. Thanks for trying to 'help' though.

[Reply #7 on:]

it's irrelevant. I've tried a much shorter 18GA wire in place of it. Of course, I still get the same result because it's unrelated to the problem. Thanks for trying to 'help' though.

Your situation is hopeless. sorry

http://arduino.cc/forum/index.php/topic,140951.0.html

http://arduino.cc/forum/index.php/topic,142587.0.html

http://arduino.cc/forum/index.php/topic,142228.0.html

[Reply #8 on:]

Thanks for your opinion. You're not able to help and you know it. I've got some new tips from people who understand the issue that I'm going to experiment with.

[Reply #9 on:]

a 3.5A power lock actuator

Would that be an solenoid / electromagnet kind of thing, and therefore the very type of inductive load that tack warns of:

but if you've got some large reactive values in there then all sorts of strange things can happen