Inverter problems

**Mastiff** · 09-30-2005, 03:22 AM

OK, now I have done just about everything humanly possible, I think. I have a '95 Chevy Suburban with dual batteries, one regular starter battery for the car and one deep cycle battery for the stereo and PC. This is charged by a really heavy duty generator - 160 amps! So I can idle run the car with full lights (including two 120 watt auxillary headlights - if I was a redneck I could hunt deer with those!), full AC, the PC running and the stereo on full blast with six regular speakers, two driven by the head unit and four (an Alpine DDD kit with treble and mid range split at the end) by a bridged 4x50 watts amp (probably around 2x50 real watts...), plus a dual 12" sub driven by a Soundstream Li'l Wonder), and I'll still have 13.8 Volts when I measure on the battery! That should be more than enough, and then some, right? When I start the car, the charging voltage is around 14.4 the first couple of minutes before it sinks to that stable 13.8.

The wires from the battery to the inverter should be sufficient, I have 12 gage on most of it, around three feet of 10 gage in a tight space, but I do see a drop in voltage of around 0.03 V without load when I first measure on the battery and then on the power cable to the inverter. Still that shouldn't be enough to create such a problem, right? What I haven't yet measured is the power directly on the inverter, after the relay. But could that be that bad? The relay is a regular auxillary lights relay.

The computer is on an inverter that stops at around 10.5-11 Volts. I use an MSI M2M Combo motherboard with 256 meg 133 mHz SDRAM, an AMD XP (think it's a 2100, but I'm not totally sure), one 200 meg and one 250 meg hard drive (all in all close to 60 000 MP3 tracks, mostly 192 kbps or more) and a 3Com Wireless router powered by the 12 V from one of the free hard drive cables. The computer has a 350 Watt standard PSU. The size of the PSU shouldn't matter, it's what the components draw that matters, right?

I use a few relays, so I have a button on the dash that powers on the inverter, and when I see the red LED in the dash that tells me that the PC's on, I can release that. Another relay connected to one of the 12 V hard drive outputs of the PSU keeps the power to the inverter going. So when the PC's off, no power goes to the inverter.

The problem is that I would like the PC to be able to run for a while without charging, like when I'm at the gas station or a shop, without having to turn off the computer. That's too much computer, not enough real big cd changer. But I can't. It will last for a few minutes and then stop. I just tried pressing the button that opens the power to the inverter when the car had been outside a standard norwegian fall night (around 6 C, 43 F), and I drove it yesterday. I tried both with the deep cycle battery connected to the PC and with the regular starter battery connected. None of them lasted more than a minute on the first attempt. The following attempts died after a few seconds.

Is there anything I can do, except perhaps to buy a Stinger battery or another very high performance gel battery for the PC/stereo? They are wildly expensive here in Norway. Shouldn't a regular 75 AH deep cycle battery be able to keep this thing running for a while? I remember when I bought the battery. I tested, and the computer ran for 45 minutes, with the stereo blasting! Is that the way it does on a new battery, and then it's all downhills? I bought that battery this spring!

Oh, and buying a 12 V PSU for the computer is out of the question because I use it both in the car and at our cabin by the sea (feeding audio to three zones, living room, bedroom and my son's bedroom). So the PSU has to be 220 V.

Thanks in advance, if anybody had the time to read this rather long post...

**Mastiff** · 09-30-2005, 05:18 AM

Hang on a second! I just found a significant drop somewhere in the relay system! I could run the computer while hooking a direct power cable from the connecting block to the inverter, and I also found a difference between chassis ground and what the inverter gets - 0.4 Volts! Now that's a lot of loss on only two feet of cable. I forgot to mention that for the last two feet to the inverter I use a computer power cable, the three pin type, so I can move the inverter between my two cars. Should such a short cable of that type loose that much power, or do I need to look in the relays and connections for the problem?

**Will Albers** · 09-30-2005, 06:49 AM

Probably not it, but do you have an isolator between the batteries? When using 2 different batteries, no isloator will make it function basically as strong as the weakest battery

**Mastiff** · 09-30-2005, 11:05 AM

Yes, they are isolated when the car isn't running, and when it's cranking. When the car is running, they're together.

**MatrixPC** · 09-30-2005, 04:51 PM

So you connect the Battery -> Relay -> Inverter? (I know the relay is to switch the inverter ON/OFF).
If so, you should try this. Battery -> Inverter. The relay should have ON/OFF switch. Now use a relay to switch that ON/OFF switch.
Just a suggestion, may not solve your problem, but definitely not hurt.

**Mastiff** · 10-01-2005, 09:02 AM

I think I follow you, but I'm not totally sure. Anyway you gave me an idea that may be my best bet by far: The inverter itself has an on/off switch on the front, and I'm pretty sure it's not on a PCB (all though if it is, it doesn't really make it any more difficult). Maybe I can tap into that with a relay and run the power and ground directly into the inverter. That should take care of any possible voltage loss!

**KyferEz** · 10-01-2005, 11:42 AM

I 2nd the "use the relay to control the inverter's switch" method.

KyferEz

**numbers** · 10-01-2005, 02:19 PM

Did you fix the voltage drop problem yet? They have a name for it, you know. It's called "FIRE HAZARD." There is nothing wrong with the way you are controlling the inverter as far as I can tell. I wouldn't say there's any need to void the warranty by opening it to rig it's switch. Just find out where the major resistance is and fix it. Your problem will go away, and you won't have to worry about burning your vehicle to the ground.

**KyferEz** · 10-02-2005, 12:14 AM

While there is no way for me to tell for a certainty from here (but Mastiff can test for it), it seems to me as though the voltage drop may be coming from the relay itself. If this was the case, using a relay rated for higher currents would certainly correct the problem, but you can just as simply hook to the switch of the inverter and avoid any voltage drop caused by a relay's contacts on the inverter's power input.

KyferEz

**MatrixPC** · 10-02-2005, 01:30 AM

To find out whether the relay is the source of of resistance is to measure the voltage at the battery and voltage feeding to the relay and coming out of the relay to the inverter.
To use a relay as a switch for inverter. You just open the inverter. There will be 2 wires connected to the switch. Now wire the wires accordingly to the relay.