Attaching a load to a car battery

[Tim Vasquez]

What's the recommended way for hooking up a typical 10-amp electrical load to the car's electrical system? Am I looking at tying in directly to both posts of the battery, or do I attach elsewhere in the engine compartment?

I thought about attaching directly to the battery posts, but (1) I worry that I might be weakening the battery somehow attaching right at the battery, and (2) my vehicle (a GM make) has one of these stupid battery connectors:

So I'm mystified how to make this connection.

Tim

 

[Jeff Snyder]

Tim,

10 amps is getting borderline in terms of what I'd consider good for tapping directly to the battery (as in using any more I'd definitely go straight to the battery). I've always replaced the GM OEM battery with a dual-post battery (i.e. a battery with a side and top post battery), since it gives you more options. At any rate, I think you can just use a ring terminal (like this one, but there are many that are more basic and several dimes cheaper) between the vehicle's positive power cable (the one pictured) and the battery terminal. Depending upon the length of that screw, you may need to pick up an extension screw as well. In addition, unless you'll need a lot of power, you'll only need to bring a positive power cable from the battery to the cab of the vehicle (or wherever you're going to put the device that'll need the power), as you can just connect the negative/ground cable to a solid piece of metal in the vehicle (scratch off any paint first to get a good ground).

If you do connect straight to the battery, make sure you fuse any cable you attach to the battery as close to the battery as possible (within a couple of feet)! There are many options for in-line fuses (with different types of fuses, an example being this one). The goal of such a fuse is to protect the cable in case any metal part of the vehicle pinches through the cable's jacket. For example, suppose you get into an accident, and the cable shorts as something from the firewall (between engine compartment and cabin) pinches it off. Without a fuse in place, tremendous current will flow from the battery, which in turn will overheat the cable and possibly lead to a fire. This is bad, obviously.

If you think you'll need more power or connections for more devices in the future, I'd suggest bringing a fused cable from the battery to a fused power distribution block in the vehicle cabin (such as this one). That'll give you more options in the future if you think you'll need them. You'll probably only need to bring a new ground (-) cable straight from the battery if you plan on drawing a lot of power (i.e. 800+ W devices). The vehicle frame is grounded to the battery in almost all cars, but the quality of this ground can be quite poor (from low-quality welds, no care to scratch off paint to get a quality ground, etc), which is why I brought a cable from the (-) terminal of the battery to a distribution block in the vehicle cabin to provide a direct ground (-) for various devices (radios, inverter, etc).

 

[Steve Miller]

Might as well throw a switch in-line too or you'll be like me and have to charge your battery every now and then due to forgetting to unplug something that draws constantly off a distribution box.
If you do decide to go with a new battery, go with an Optima!

 

[Dan Robinson]

The fuse panel/busbar under the dash in some cars (just above the gas/brake pedals in my car) has a few extra terminals that you can connect accessories to. My inverter is wired into this panel. The inside dash panel is protected by a large fuse on the main fuse panel under the hood. I have another inline fuse for the inverter just before the connection to the under-dash panel.

The under-dash fuse panel has heavy gauge wire already running through the firewall, which makes for a solid inverter connection that I've not had any voltage drop problems with. Getting a new set of wires through the firewall in late model cars is not going to be an easy job. In my car, the under-dash panel was a sufficient place to make the connection.

I did the same thing Steve did - I wired a master switch to my inverter/threatnet receiver that I can shut off from the driver's seat (my inverter/threatnet panel is between the second row seats). It's saved me from having to get a jump many times.

 

[Jarrod Cook]

Tim,

I have a GM car with the same type of battery connections. There should be a positive access post for doing things like this, usually near the battery. They put that there so you can access the positive terminal (for jump starting or running accessories) without having to mess with that little stub. Mine has a red plastic cap over it.

As for the ground you can usually find a good bolt in the engine compartment somewhere that you can put a ring connector on that serves as a decent ground.

 

[david diehl]

another thing you can do is attach a solenoid after the battery. This will shut off all radio, inverters, escetera wen you turn the key off. I know that the police cars, and ambulances in my area have this installed. Just a thought, I prefer to leave the radios to where I can shut them off on my own, but my inverter is wired to the fuse block so it shuts off when I turn the key off

 

[Jason Foster]

Fuses, Fuses, Fuses.

Tim:

It's been said, but make sure you fuse everything. Additionally, leave the connection of the battery until the end, after you've checked over everything twice.

I've done many mobile installs, and I'm pretty good at it. However, the one time I rushed into an install and didn't take the proper measures......
........

Previous thread: http://www.stormtrack.org/forum/showthread.php?t=16667

....this is what happens. That was my ride this past May. I think I was just looking for an excuse to get a new chase vehicle....

One solution that I've used for smaller items is to remove the existing 12v (15-20amp) power outlet, cut the wires, splice in extended wires to my new console or area I need the outlet. I place a set of fuses (I do both positive and negative fuses) along the extension, and then add a new outlet (cigarette style) that has two or three available outlets. I also make sure to clearly mark the voltage and amperage maximums, so as not to confuse the set that is connected directly to the battery (for the higher amperage items).

Of course you did say for the engine compartment, so if that is the case, then I think the other options is to just add ring terminals (as mentioned earlier). But you don't have to replace the entire battery to get the standard posts. You can simply get adapters, that allow the GM wiring to remain attached to the battery, but give you posts to attach additional items to.

 

[Jim Saueressig]

I would fuse it right at the battery ( within a few inches ) and then run to a quick disconnect you can attach nearby and then on through to wherever you are going, make sure the wire is tied up snug in route and be sure to use some rubber grommets or something to protect the wire on any holes you go through or drill. Make sure you are not routing past pinch points or any thing that moves. Depending on your vehicle (age) you can also sometimes ground right at the alternator bracket as well with the main battery / vehicle ground.

The main causes of fires or shorts will be because first of all a person didn't fuse and then left wires loose and they burned and shorted on exhaust manifolds or pipes and or got cut into and shorted where it was run through the firewall or other metal hole. Making sure you have a good ground for the equipment is also important.

The other idea that was mentioned about the dual post batteries is also very handy.

 

[Tim Vasquez]

UPDATE: Here's what I did.

I connected the + side to the separate terminal post provided in the engine compartment using a ring terminal like Jeff suggested.

I was going to connect the - side to the battery, but I wasn't even able to insert a ring terminal in there, as the battery screw (pictured at top) was short and the face of the OEM battery connector had a textured face meant to sit flush against the battery terminal. So I gave up and attached the ring terminal to a bolt elsewhere in the engine that attached to the vehicle frame.

I put an inline fuse coming off the + post.

Hopefully that was sufficient to make the hookup safely! Appreciate the advice.

Tim