connecting batteries - newbie

[marcusn]

I'mgoing to parallel two batteries together.
Pos to Pos, neg to neg. Pos from one battery to switch, neg from other battery to switch.

Is there any particular order I need to make the connections to insure no shock?
If the master switch is off, is the electrical loop open and safe?

Thanks

[sailingdog]

Marcusn-

Be careful... the batteries have enough amperage to kill you if you're not. As long as the terminals aren't covered on the batteries, they are dangerous. I hope your installation has the batteries in battery boxes and that the terminals on the batteries are covered.

Hook them up in this order. Positive to Positive, Positive from one battery to the switch. Cover the positive terminals at this point. Then hook up Negative to Negative, and the negative can be from either battery, but shouldn't go to the switch—it should go to the ground side of the DC panel.

Where this is located and how it is setup depends on how your boat is wired. On some boats it is a bus bar setup, on others it is separate terminal blocks, on others it is part of the DC panel setup.

The main battery switch should have the positive coming in from the battery bank, and the common lead should go to the hot side of the DC breaker panel.

[Omatako]

SD
Quote "batteries have enough amperage to kill you"

??? Are you sure?

I've been working with batteries for a heck of a long time and I've never heard that statement before.

Andre

[gc1111]

Why do people have such trouble understanding the difference between amperage and voltage and amp-hours? I have seen many statements in sailing related communications that are incorrect in this understanding.
Batteries are dangerous only in the amount of heat they can release. 12v or even 24v will not send enough current through the body (except in very unusual situations) to be dangerous. However a wrench dropped on battery terminals can generate enough molten metal to pose a danger. Be especially careful of wearing rings (e.g. wedding rings) while working on batteries, they can cause you to lose a finger.
The most intuitive analogy is to water in a hose. Pressure is akin to Voltage. Amount of water flowing in a second is analogous to current (amperage). The total volume of water that flows out is analogous to amp-hours.
The thing that melts metals is the large amount of current that batteries can release. The energy is released at a rate of volts x amps (= watts). With a high amperage the energy is released very rapidly resulting in flying, burning metal (sparks) and molten metal.

[sailingdog]

Andre-

It isn't the volts that generally kills you.. it's the amps. Static electricity generally runs in the thousands of volts...yet due to the low amperage you generally live when the door knob zaps you. Under the proper conditions, a 12 V battery has plenty of amperage... and just enough voltage to kill you.

[Rockter]

NEGATIVE OF BATTERIES TO GROUND !!!!!

Ground for me is on the motor.

Don't put different polarities to the battery master switch !!!!!!!.
Whan you close the switch you will just short the batteries and you will have massive fire.

[Idiens]

Originally Posted by sailingdog

... a 12 V battery has plenty of amperage... and just enough voltage to kill you.

I think you got that wrong SD. You can hold both terminals of a 12V battery and hardly feel anything. 110V is a different matter. Electric welding kit usually runs at 3 to 6 V, but the amperes.... Or put another way measure your left-hand to right-hand resistance with an Ohm-meter, about a meg-ohm. V=IR for DC, so 12V can push about 12 micro-amperes through you.

[Gary M]

It takes about 70 ma of current across the heart to put it into fibrilation. At that point without help you are in trouble. The most dagerous path for electricity is from hand to hand since it crosses the heart. Electricians tend to "keep one hand in their pocket".

Generally 12 volts is not a problem since your skin resistance is so high that there is not enough current to hurt you. As has been stated the greatest dange from 12 volt battieries is to short across them, that can cause a nasty flash which may injure you. In particular I would be worried about potential damage to the eyes.

You also should keep in mind that batteries on a fast charge give of hydrogen. If it is trapped in a battery box etc. and you cause a spark you will get a little bang. Probably not serious but enough to catch your attention.

Gary

[ebs001]

SD is correct that it is the amperage that kills you not voltage. A 12 volt battery, however, does not have enough voltage to push enough amperage to kill you. Ohm's law E=IR. The amperage usually quoted that will kill you is 10ma, that's why GFCIs are designed to trip at 5ma.

[sailingdog]

If your skin is wet with salt water... you become much more conductive to electricity... Being very cautious around the batteries is generally wise. Yes, under normal circumstances, 12 VDC isn't sufficient to electrocute someone...but accidents happen, especially if you mix salt water and electricity.

BTW, pure water is a very poor conductor of electricity... Salt water is a very good conductor of electricity.