Car's power capabilities

**claylong** · 11-27-2002, 06:10 PM

I have a chrysler lhs, with a 90 amp alternator. I am going to be running my system off a 400w inverter that i picked up cheap. Two PSUs will run off the inverter, an ATX psu for the motherboard, HDD, and then a small 120VAC -> 5v and 12v dc supply for the display, touchscreen, and the dvd drive up in the dash. I have tested the equipment and everything seems to be working fine, except for one thing. When I have a couple devices on in the car (lights, wipers, etc.), the computer running, and I slow to a stop, my inverter *beeps* with a low voltage alarm.

I want to fix the problem, i have a few questions.

My first idea was to get a bigger alternator, but it seems that is not really an option for my car. I did know of a police Intrepid with a 140 amp alternator, but I cant seem to find one to purchase.

Second i thought of a tank circuit, but then i realized that not only would i need a really big cap, but the charging of the cap would drain the electrical system pretty heavily.

What about a second battery. I looked around the board and read up on what most people are doing with dual batteries. I have access to a fairly cheep battery isolator that might help, but the question is, won't a second battery drain the system (eventually)?

I guess i need to better define the problem. If the alarm sounds when i stop, does that mean that when I am running, the battery is being drained? I understand there is only so much power in the system, and none can be 'created' by adding a circuit or battery.

Any ideas, or maybe a clarified explanation of what i am saying?

**zootjeff** · 11-27-2002, 06:47 PM

What gauge wire are you using?

Are you plugged into a cig outlet? Please say no.

Did you run heavy gauge wire from the battery straight to the inverter? Please say yes.

**zootjeff** · 11-27-2002, 06:48 PM

Another option is to increase your idle speed.

**Aaron Cake** · 11-28-2002, 09:40 AM

A larger alternator is the only proper solution (besides beefing up the wiring...thicker wires from your battery and alternator will help). No doubt that there is an upgrade available. Alternators are very simple creatures, and most of the time can be swapped with a few minor wiring changes (assuming it physically fits). So try looking at other Chrysler cars that have larger alternators for a source.

If you can't swap, most alternator/starter shops will be able to rewind your existing unit to put out more juice.

Do not increase your idle speed. It will effect too many other things (including emissions tests) in a modern vehicle and will cause all mannor of problems (from check engine lights, to "limp" mode, to who knows what else).

**eugenen** · 11-28-2002, 06:58 PM

I always understood that higher power alternators put out less current under idle as well. I had the same problem with the Chrysler we used to have, it couldn't even run all its power accessories (rear def, lights and wipers) without giving it gas to keep the rpm up.

**Aaron Cake** · 11-29-2002, 09:24 AM

So put a smaller pully on the alternator.

**PTCruiser** · 11-29-2002, 09:34 AM

Get a DC-DC power supply...

http://www.opussolutions.com/150watt.html

It's should be enough to power your system!

Inverter are really not efficent...

**claylong** · 11-29-2002, 02:27 PM

First of all, the wire situation is taken care of. At one point i was using wire fit for > 100 amps and the problem still occured. Good point, but it would be too easy

Second, I am not sure that messing with idle speed is my idea of a problem solver. Although, it would stop the problem from occuring.

Third, a re-wound alternator is my best option yet. I thought that it could be done, but I have yet to talk with anyone that has confirmed the idea. I will make a few calls next week. The small pulley is a great idea too.

Lastly, I have added some equipment since my sig file, and now have a PIII 933 processor and board, along with many other accessories, and i believe that I NEED a 250w supply. I would like to get a Dc-DC, but I have had too much trouble trying to get one, and too many people want more than $160 for used supplies.

Thanks guys!! Any other ideas, bring them on.

**Telek** · 11-29-2002, 07:07 PM

you certainly don't NEED 2 power supplies and I would doubt that you even need 250W for your one power supply.

do you have an ammeter? can you hook one up to your system and tell us how much power it's actually taking?

alternators have a built in voltage regulator in them so that they're always putting out the 14.4V (or whatever it's regulated to)... so once the rpms go down the output power capacity drops which is why your system is whining at idle... however unless you're really drawing a LOT of power out of your system (which I suppose is possible if you're running all of your accessories) your battery might be shot to begin with. Can you tell us the voltage that your battery is at after running with the car off for a few minutes?

Hooking an ammeter up to your computer setup will help as well to tell us what you need.

Hooking up a second battery should also help your problem and shouldn't cause any additional issues either (especially if you use a few large diodes to prevent the battery from draining into the car's electrical system, only able to be charged from it)