help with car battery charger connections

What are you hooking the battery minder to ? Most modern cars will have the negative terminal grounded to the frame. Also most other common equipment will also such as riding lawnmowers.

Nearly all cars, motorcycles,ATVs etc are negative ground today. To be sure just look at the connections. The ground cable will go straight from the battery to the engine block or frame. The other cable goes to a post on the starter with a smaller wire going to provide power to everything else.

Really all you need to know is which terminal is which and they should be marked right on the battery.

What they are doing is having you make the connections in the way that is least likely to cause a spark near the battery.

With the charger not plugged in connect the charger wire to the post that is not grounded. Since the other post is connected to ground you can connect to most any bare metal you see and it will be the same as if you had connected to the ground post on the battery. By choosing a spot away from the battery you don't have to worry about there being a small spark that could set off hydrogen produced in the battery.

Keep in mind this has all been written with lawsuits in mind. In practice there is little if any spark when making connections with the charger not plugged in. Hydrogen is produced when the battery is charged, so the time you most need to worry about it is when disconnecting the charger. If the caps are on the cells and you allowed any hydrogen produced to dissapate there is nothing to worry about. IMO the most danger due to hydrogen (or gasoline fumes) would be one a boat.

On many battery tenders for motorcycles there are wires, about the same weight as those on the charger, that can be attached to the battery and allow a remote connection without lifting the seat to get at the battery. One of these would also move any possible spark away from the battery. (They don't need to be 6-gauge, about as thick as your little finger, as suggested in the directions. We are talking about a 1 amp charger here.)

Find your battery + terminal. The battery is normally marked (+) and (-).

The + is often red and the - is often black.. But not always.

Follow the cables from the battery and see which one is connected to the chassis. That will tell you which terminal is grounded, NOT which is + or -.

Now, positive (+) is positive no matter whether it is grounded or not. Same for negative (-).

If you have a modern car, the negative terminal is grounded. You can verify this with a meter or a light bulb; connect it between the positive terminal and the chassis and the lamp will light.

If you have an MG, Morgan, Kallista, Zil, Lada, or some very old Fiat models, there is a possibility you have a positive ground. In that case, you have plenty of other more serious worries to contend with.

Yes. Batteries produce explosive gas, and when you make the final connection there will be a spark. Your goal is for that spark to be far away from the battery. So you connect the positive lead to the battery, then you connect the negative lead to some chassis point away from the battery. Likewise you disconnect the negative lead first. That way, the spark is not near the battery.

--scott

Another way is to put a damp towel or rag over the battery.

Positive (+) really is Negative (-) and Negative (-) really is Positive (+) but don't expect the Society of Automobile Engineers to ever change the books on that! cuhulin

Convention current flow is from + to - Electron flow is from - to +

Make up your mind which convention you're using. Don't expect J.Q.Public to ever get a handle on this one.

The Brits had it right the first time.(wouldn't Jeremy Clarkson be oh so proud?) Of course they call it Earth/Ground.

Years ago, I worked at a factory (Hi Joyce) that manufactured batteries for cars and trucks and golf carts and riding lawn mowers.Two or three times each year we manufactured a couple of pallet loads of old fashioned six volt batteries for MG cars.One time, one of those big extra heavy 18 wheeler truck batteries slipped off of a roller line and broke the middle toe bone in my left foot in two places. cuhulin

Nearly all modern cars are negative ground -- I'd say "all", but then someone would come up with some oddball example. Certainly any American or Japanese car built in the last 40 years will be negative ground, 12 volt. If in doubt, you could measure the voltage between each terminal and the car chassis -- the ground terminal will show no voltage, the other terminal will show full voltage. This is something you could do with a light bulb if you don't have a meter.

Positive is positive by definition. Classical current flows from plus to minus regardless of the direction of electron flow. Maybe it should have been changed, BUT it still confuses a lot of engineering students who feel it shouldnt be that way.

What is confusing is that military electronics training for many years talked about current flow in the opposite direction. It was a bit of a shock for folks who learned electronics in the military to get out into the rest of the world and find the signs all reversed in all the equations.

--scott

It sure is a problem. The classical definition was taught in universities for years. Now we have an evolving dual system. It is a little like the metric system....it works fine either way, but it would be good to settle on one or the other.

The classical definition comes from Benjamin Franklin. He believed (and it seems perfectly reasonable) that lighting comes down from the sky and therefore the direction of current flow is from the sky to the ground. He used this to define positive and negative, saying the cloud has a surplus of charge and the ground a deficit.

But, it turned out that he was totally wrong, and in fact lighting travels from the ground to the sky (when it is "cloud to ground" lightning). So the current flow is in fact opposite of Franklin's convention, and the charge is carried by a particle, the electron, whose charge is defined as -1. That's how we got into that particular craziness.

I don't know when the military started doing otherwise, but I know all of the WWII through Vietnam era military training stuff talked aboout current flow in the direction of electron flow. I have seen one WWI manual "Principles of Telephony and Manual Telegraphy" which also used that convention although I don't know if it was standard at that time.

--scott

Well, when semiconductors were invented, "hole" movement was a validation of positive charge flow...after a sort. So the model turned out not to be wrong, just a little premature perhaps. ;>)

Some of the trucks I saw and drove in Vietnam had two batteries.They also had air compressors for the brakes.Every morning I had to wait about five minutes for that loud air compressor buzzing noise to stop buzzing. cuhulin