Thread: Having problems with my inverter... any ideas?

dc-dc isn't exactly the answer i mean i got the parts i needed to build my converter but then i got reading the parts info and well the maxim ics i have aren't supposed to be used below 0degrees celcius when it's currently about -10 on average and i'll probably see -30 before the winter is over. so if you get the wrong components then there isn't any difference besides if the car is warm and the inverter is warm why would that be any different than the dc-dc converter ?

Ok, so I guess it's time to go DC-DC. Are there plans for building your own or what's the cheapest commercial one?

chris

I really think it's the battery. I have a pretty big alternator (115 amps!!) it's a 96 Maxima. But like I said it's still the OEM battery so it's 4-5 yrs old. I bet that's it. What battery should I look at? Optima? They're like $150 - anything cheaper?

Chris

This is an old post, but I ran across it doing some other research on Google, so I'll address the points I find here:

First of all, just because you have a 115 amp alternator, does not mean that it is constantly putting out 115 amps. That means the peak output of the alternator under a full load is rated at 115 amps. The alternator I have in my '97 Mustang is a 130 amp alternator (stock), but at 1500 RPM, it only puts out ~65 amps. And even less when idling (at 750 RPM). So alternator output varies with engine rotation speed.

Second, DC-DC conversion is more efficient, but subject to the same pitfalls as DC-AC inversion. The more extreme the temperature (either hot OR cold), the less efficient the conversion process will be. Also, as with any kind of conversion, there is not 100% efficiency. So if you are pulling 300 watts AC out of an inverter, the actual current drain on the inverter's input line would be more than 25 (300/12) amps. There is overhead. Assuming a 90% efficiency (which may be giving your inverter more credit than is due), this would mean that you would actually be pulling 27.5 amps on the input line for a steady output of 300 watts.

Most automotive relays are rated for 20, 25, or 30 amps. Check the ratings on yours to make sure you're not overtaxing it. Also, make sure your wire gauge is thick enough to allow the passage of current. If you are using thin wires, it is entirely possible that when the wires are hot (regardless of inverter and CPU temp), they will pass the current more efficiently and allow your computer to run. But, in the extreme cold, they cannot pass enough current to allow operation.

Optima is a good cel battery, but if you're going to spend the money, you should go for a Yellow Top. This is Optima's deep cycle industrial battery. It will take a beating and last you for many years to come. It can be completely 100% drained, and then be brought back to full charge without damaging the battery (unlike a normal car battery). However, you should be careful not to do this while the battery is in your car, because the increased charge requirement will overheat your alternator. Charge your battery to a minimum of 12.6 volts (tested under load) before you charge it using the alternator--at least that's what the alternator's manual suggests.

cenwesi: There is not enough information available in this post to determine that the problem is 100% with the inverter. It could be with the alternator (output from alternator could be falling as the alternator starts to fail), wires (I've explained why the wires could be to blame), perhaps the computer itself (at such an extreme temperature, could be taking more than the 300 watts to power it), or any other number of components.

I hope I have addressed all the issues in this post, so that if (like me) somebody runs across some useful information in it despite it being 6 years old now, everybody is better informed. As always, any questions, feel free to e-mail me: eslindsey {at} gmail [dot] com.

-Eric