Battery trickle charger connections

[Volfy]

Most of the kids these days rely on those internal resistance testers rather than actual load testers of yesteryear. Load testers still exist, but they are certainly not popular these days.

There might be new-fangled chemistries purveyed about these days, but what a car starter battery needs to do haven't changed since it was first put into automobiles more than a Century ago. Neither has the type of test(s) that can tell a healthy car battery from a questionable one.

A load tester mimics the short-duration high-amperage load a starter battery must deliver when cranking over an engine. Cheap. Fast. Simple. Direct. Effective.

 

[5tinger]

Would there be any risk of damage caused by charging battery from the fuse box instead of connecting charging leads directly to battery?

 

[Thomby]

Would there be any risk of damage caused by charging battery from the fuse box instead of connecting charging leads directly to battery?

No, it's designed to be a jump point, and the max current your battery sees while charging (10-25 amps?) is a tiny fraction of what your starter motor pulls (200-500 amps?). The resistance from front to rear is negligible, and you aren't passing anywhere near enough current to generate noteworthy heat.

I would suggest putting a multimeter across the front & rear connections to see if you can even measure the resistance, but the resistance of the probe lead extensions you'd need to reach would drown out the resistance you're trying to measure.

 

[D.J.]

Would there be any risk of damage caused by charging battery from the fuse box instead of connecting charging leads directly to battery?

I don't think there is any risk, but for a more informed opinion, what charger are you considering using through the fuse box, and which fuse box (the under hood fuse box?), and also, why?

 

[Volfy]

Would there be any risk of damage caused by charging battery from the fuse box instead of connecting charging leads directly to battery?

The slight voltage drop across the longer distance to the battery will cause your charger not to charge your battery as accurately as having a very short charge lead. Not a huge deal, as the car's own charging system has the exact same problem. Not sure if OEM engineers took this into account and compensated for it, but aftermarket batt chargers for sure have no way of knowing how long your charging leads are.

 

[D.J.]

The slight voltage drop across the longer distance to the battery will cause your charger not to charge your battery as accurately as having a very short charge lead. Not a huge deal, as the car's own charging system has the exact same problem. Not sure if OEM engineers took this into account and compensated for it, but aftermarket batt chargers for sure have no way of knowing how long your charging leads are.

The voltage drop as the battery reaches a full charge would be insignificant. Some rough calcs show

For a ~15-foot long, typical 4-gauge wire with a current of 1 amp, the voltage drop would be approximately 0.0075 volts.

 

[Volfy]

The voltage drop as the battery reaches a full charge would be insignificant. Some rough calcs show

For a ~15-foot long, typical 4-gauge wire with a current of 1 amp, the voltage drop would be approximately 0.0075 volts.

That only applies to the positive lead. The negative side uses the car body as return path. Then the conductor path might go thru spot welds that join the pieces of steel sheet metal to form the entire unibody. Then there are the bolted ground connections and such. Im lucky I live in the warm south and those connections tend to stay fairly corrosion free. Not so up north in the rust belt.

But, it's your preference. I had a choice of where I want to install the SAE charging pigtail, and direct to battery terminals was actually the simplest and neatest way. If not in use, the pigtail hides under the trunk floor out of the way and stays clean out of the elements. The way we park out cars, rear end also is the most convenient to hook up a charger. Makes zero sense to me to hook it up any other way.

Your mileage may vary.

 

[Thomby]

The negative side uses the car body as return path. Then the conductor path might go thru spot welds that join the pieces of steel sheet metal to form the entire unibody. Then there are the bolted ground connections and such.

Back in my car audio days, this was the argument for buying or creating ground strap kits to chain together the battery, strut towers, engine block, etc more definitively.

I made one as a teenager, as much an exercise in crimping & heat shrinking as anything, but the counter argument was that if you couldn't measure any effective resistance between ground points, and didn't have any ground loop hum, you'd also have no real voltage drop and stringing 12 gauge around was redundant.

 

[D.J.]

That only applies to the positive lead. The negative side uses the car body as return path. Then the conductor path might go thru spot welds that join the pieces of steel sheet metal to form the entire unibody. Then there are the bolted ground connections and such. Im lucky I live in the warm south and those connections tend to stay fairly corrosion free. Not so up north in the rust belt.

But, it's your preference. I had a choice of where I want to install the SAE charging pigtail, and direct to battery terminals was actually the simplest and neatest way. If not in use, the pigtail hides under the trunk floor out of the way and stays clean out of the elements. The way we park out cars, rear end also is the most convenient to hook up a charger. Makes zero sense to me to hook it up any other way.

Your mileage may vary.

It would be interesting, to measure both the voltage drops while cranking between:

• Battery positive terminal and starter motor positive connection
• Battery negative terminal and starter motor ground

Using calibrated equipment, and then compare them while cranking the engine, and then compare those 2 voltage drops to see which is greater.

I'm not actually going to do that, but I would be curious. My assumption is that they are both very similar.

 

[5tinger]

I don't think there is any risk, but for a more informed opinion, what charger are you considering using through the fuse box, and which fuse box (the under hood fuse box?), and also, why?

The charger is a 15Amp (smart type)
The fuse box that has the positive probe and using the provided negative stud nearby on the frame.

Connecting charger directly to battery at the rear of the vehicle would require far more effort.

 

[D.J.]

The charger is a 15Amp (smart type)
The fuse box that has the positive probe and using the provided negative stud nearby on the frame.

Connecting charger directly to battery at the rear of the vehicle would require far more effort.

The connection you are talking about is connected directly to the battery, it is for all intents and purposes, the same connection.