Power Questions

[unabashedpraise]

I had my trailer lights connected straight to the battery but was going to be adding some extra lighting and have a power inverter hard wired. I didn't want everything taking up space in the already cramped battery post location. Instead I used an old xm radio dock and made a power dock for my 12 v connections. The positive is connected to the engine fuse box and grounded on the firewall.








Is this plastic ok for the connections? Will it overheat?

I want to run a heavy wire to the rear of the vehicle then attach the power inverter, after market lights, and a 12 v plug. Is 8 gauge heavy enough? Should aftermarket lights and my power inverter be attached directly to the battery?

I probably should have asked these questions before I started....er finished.

 

[dwh]

Dunno what that plastic is, but it's probably not heat rated. Most wire insulation is rated 60C, 75C and 90C, so if it can handle that, it should be fine. If you are overheating the wire beyond its insulation rating, then you've got other problems.

Is 8 heavy enough? Depends. Probably fine for the lights and 12v plug, but for the inverter? Lemme just pull a number out of my ...uh... hat. I'll say it's a 600w inverter.

600w / 12v = 50a

Generally, #8 is rated for 40a, not 50a. Plus, since you'll be supplying a load, as the battery voltage drops, the amps will rise, so even if you didn't run a 600w inverter at full load, eventually you could exceed the rating of #8.

For a 300w inverter 8 would probably be fine.

 

[unabashedpraise]

The wire I used for the docking station is from previous battery installations that I had lying around. Any suggestions on how to test the plastic? I may just pick up a plastic junction box at the store and cut it to fit.

Also, if my 12v plug is rated for 150W, is it ok to use it to charge my battery jumpstarter and/or use the 400w inverter? I didn't know the rating on the 12 v plug until after it was installed. There was only two to pick from at the store anyways. Do I need a higher wattage plug?

 

[unabashedpraise]

also found this to help with figuring out what size wire to use.

http://www.tessco.com/yts/industry/products/itm/automotive/get_wired.html

 

[unabashedpraise]

As someone pointed out I did not list the inverter size. Ironic since I brought it in from outside just to do that when I wrote the post.... It is a 400w inverter, with a 40 amp fuse in the inverter itself with the option to be hardwired or plugged in via a 12v plug with an inline 20 amp fuse.

 

[dwh]

400w / 12v = 33.3a

Dunno what its surge rating is, but if you don't go over 400w on it, #8 would be fine.


With a 20a fuse, then you would be limited to:

20a x 12v = 240w

So, if you draw over 240w then you'd melt the 20a fuse.


As to the 150w rated 12v plug - you can use it, as long as you don't draw more than 150w.

For an inverter that size, I'd go hard wired if I was going to regularly draw 400w.

 

[unabashedpraise]

My inverter has been hardwired to the rear cargo area, I used 10 gauge based on the previously posted link and wire availability. However, I never noticed before that the inverter has an annoying blue light that stays on when powered, even when switched off. I was thinking of clipping the light or adding a switch near the drivers area to shut the main power off. I actually like the switch idea. Would I need a relay and a switch? I'm not finding any 40a switches that don't look like missile launch controls.

 

[4x4junkie]

I would suggest wiring the inverter using at least #6 wire to minimize voltage drop, allowing the unit to run as efficiently as possible.

If the inverter is, for example, 12' away from your battery, with #10 wires you'll have a 6.9% voltage drop @ 33 amps which is getting fairly close to a volt lost at 12V, possibly causing the inverter's low-voltage cutoff to kick in before it reaches full output (especially if your battery isn't quite at full-charge). With #6 wires, it's a 2.7% drop, or about 0.3 volt.

40A switches are gonna be pretty heavy-duty. I'd try to measure what the inverter's current draw is when it's switched off. If it's less than 25mA or so, I'd just put a piece of tape over the blue light (LED, I'd assume) and call it a day (the light itself is probably good for 10-20mA, so clipping it should reduce the current by roughly that amount).

 

[unabashedpraise]

Since I already ran the 10ga wire I will wait and see if I have any issues before switching to anything bigger. The good news is I made it easily removable so I could use the original power cord straight to the battery if I need it for something requiring more power.

My jeep seems to have a little gnome inside that causes the battery to drain if we don't drive it every 4 or 5 days and want to keep all unnecessary power systems turned off. I have an aftermarket alarm/remote start that can be used from quite a distance and I wonder if that is what's causing it. Or it may be when the wife drives it back and forth for days in a row to the gym which is about 1 mile away. Either way the battery was replaced Dec '11 but we are still having issues so I purchased a jump pack. I plan on getting a new battery next year and using this one as a dual battery setup in the jeep or in the trailer I have planned.

Since the 40a switches are that big, would I just get a 40a relay and buy a switch? What kind of power requirement would I need for a switch?

 

[4x4junkie]

Alarms definitely can be a culprit for a drained battery (easy way to check is put a current meter on the wire supplying the alarm's power, greater than 100mA or so and you've found the problem).

You can use pretty much any type of switch you want to control a relay (the relay coil needs maybe 0.1 amps for it to operate). I have a row of miniature toggle switches that control relays for the lights on my rig. Only thing maybe is if you use a particularly small switch, you might want to put a clamping diode (1N4001 or similar 1-amp diode) across the relay's coil so that the switch's contacts won't get eroded by the spark that forms each time you break (turn off) the connection.

 

[unabashedpraise]

Auto parts store tested the 2 year old battery and replaced it though they said it looked like the alternator is only charging at about 40% output....whatever that means from a guy who works behind the counter. He wasn't sure if he was reading volts, amps, or milliamps. Either way he said the graph showed a min and max level and it was below the halfway mark but not quite to the min.... And he broke my battery tray where the bolt screws in.... Sheesh.