tomdrobin
Perry, MI
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Joined: 06/20/2003
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Yahooligan wrote:tomdrobin wrote:I don't understand the arcing comment though. If something is drawing current, you can get an arc on either cable when connecting or disconnecting.
You are much less likely to get an arc/spark, if at all, when you do the ground last. Why? Due to the way electricity flows. There is little to no current flowing through the ground, all the load is on the positive side of the battery. Anything that produces a load on the battery pulls the energy from the positive side, by connecting the negative first the circuit is almost complete. Anything that is going to pull current will pull from the + side, and if it's substantial then you will get a substantial arc.
By connecting + first you avoid the potential for an arc, anything that is going to pull a load will still pull from the + side regardless of which is connected first, anything that makes its way back to the ground will be residual and is typically not enough to cause a spark. Electricity doesn't flow backwards here.
Also by connecting the - last there is no power spike headed towards your electronics, doing the - last means whatever is pulling a load only pulls what is needed for the load and not what is needed to arc, which is a lot more energy, which then gets fed into your electronics.
You'll be hard pressed to find any battery mfr that says NOT to connect + first and - last for all the reasons stated in this thread.
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tomdrobin
Perry, MI
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Joined: 06/20/2003
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tomdrobin wrote:Yahooligan wrote:tomdrobin wrote:I don't understand the arcing comment though. If something is drawing current, you can get an arc on either cable when connecting or disconnecting.
You are much less likely to get an arc/spark, if at all, when you do the ground last. Why? Due to the way electricity flows. There is little to no current flowing through the ground, all the load is on the positive side of the battery. Anything that produces a load on the battery pulls the energy from the positive side, by connecting the negative first the circuit is almost complete. Anything that is going to pull current will pull from the + side, and if it's substantial then you will get a substantial arc.
By connecting + first you avoid the potential for an arc, anything that is going to pull a load will still pull from the + side regardless of which is connected first, anything that makes its way back to the ground will be residual and is typically not enough to cause a spark. Electricity doesn't flow backwards here.
Also by connecting the - last there is no power spike headed towards your electronics, doing the - last means whatever is pulling a load only pulls what is needed for the load and not what is needed to arc, which is a lot more energy, which then gets fed into your electronics.
You'll be hard pressed to find any battery mfr that says NOT to connect + first and - last for all the reasons stated in this thread.
I disagree. Fundamental electrical theory. In a series circuit current flow (amps) is the same everywhere in that circuit. The same amperage flows in the negative and positive terminals. Voltage spikes are most likely to happen on disconnect because if current is flowing in an inductive load (any kind of coil ie; motor) that current builds up an a magnetic force. Upon disconnect that magnetic force will create a spike much higher than the source voltage. The reasons for recommending hooking up the negative last and disconnecting it first are to avoid an arc from the postive if your tool touches something at ground potential.
Voltage = potential difference (EMF) = pressure
Amerage = current flow
Power = amps x volts (ohms law)
I'm not infallible for sure. But, that's the way I understand it.
I've a degree in electrical engineering tech.
NIASE Master Mechanic
25 Years As an engineering tech for GM engineering.
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Yahooligan
Temecula, CA
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Joined: 11/05/2007
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tomdrobin wrote:tomdrobin wrote:Yahooligan wrote:tomdrobin wrote:I don't understand the arcing comment though. If something is drawing current, you can get an arc on either cable when connecting or disconnecting.
You are much less likely to get an arc/spark, if at all, when you do the ground last. Why? Due to the way electricity flows. There is little to no current flowing through the ground, all the load is on the positive side of the battery. Anything that produces a load on the battery pulls the energy from the positive side, by connecting the negative first the circuit is almost complete. Anything that is going to pull current will pull from the + side, and if it's substantial then you will get a substantial arc.
By connecting + first you avoid the potential for an arc, anything that is going to pull a load will still pull from the + side regardless of which is connected first, anything that makes its way back to the ground will be residual and is typically not enough to cause a spark. Electricity doesn't flow backwards here.
Also by connecting the - last there is no power spike headed towards your electronics, doing the - last means whatever is pulling a load only pulls what is needed for the load and not what is needed to arc, which is a lot more energy, which then gets fed into your electronics.
You'll be hard pressed to find any battery mfr that says NOT to connect + first and - last for all the reasons stated in this thread.
I disagree. Fundamental electrical theory. In a series circuit current flow (amps) is the same everywhere in that circuit. The same amperage flows in the negative and positive terminals. Voltage spikes are most likely to happen on disconnect because if current is flowing in an inductive load (any kind of coil ie; motor) that current builds up an a magnetic force. Upon disconnect that magnetic force will create a spike much higher than the source voltage. The reasons for recommending hooking up the negative last and disconnecting it first are to avoid an arc from the postive if your tool touches something at ground potential.
Voltage = potential difference (EMF) = pressure
Amerage = current flow
Power = amps x volts (ohms law)
I'm not infallible for sure. But, that's the way I understand it.
I've a degree in electrical engineering tech.
NIASE Master Mechanic
25 Years As an engineering tech for GM engineering.
Would this apply regardless of what type of circuitry is connected?
Here's where it gets confusing (for me).
Take a 12v, 10w bulb and connect it to a 12v battery. Assuming exactly 10w, that would be 0.83A draw. Using a DVOM in series with the bulb on the + side for the bulb in question showed an actual draw of 0.9A. Moving to the - side showed -0.9A (flow from the bulb to the battery vs. battery to the bulb). In typing this out and re-reading what you said, I think it's a little more clear to me. I took your post to mean there was current being drawn from both sides, I should've taken flow literally; Current was flowing back into the battery.
Now, that said, and safety reasons aside, would and arc on the - side at the power source cause the same spike across the entire circuit as an arc on the + side at the power source? I suppose it would have to otherwise it wouldn't arc, being a loop it wouldn't matter where in the circuit this occurred.
In fact, when it comes to electrical connectors the negative is almost always, if not always, the first to connect and last to disconnect due to the ground pin being longer from what I've seen.
So I was wrong with my previous post, it happens.  At the end of the day I'm happy to have learned something new and hope other people come away learning something as well instead of being more confused.
I appreciate you taking the time to explain this in more detail!
--
Hogan & Clan
2005 Nissan Titan CC SE 4x4
2010 Keystone Hideout 31BHSWE
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John H
Kansas City Mo.
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Joined: 04/11/2002
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All in all, For my self I thank both tombrobin, & yahooligan for you educational debate, for both of you trying to pass on their knowledge. But, for the conclusion at the last two post, allowing me and maybe others like my self to want to know the question of, "WHY" ??? If I can understand the reasoning behind a situation, why. I am in a far,far,far, better position to implement a decision. Knowing why that it is the right way. Rather than on the other hand, doing what everybody says to do, & not knowing why, or in reality if that, they or it, is really right. It goes back to the axiom's, "Knowledges (TRULY) is Power", or "To Know is to be Forewarned". Thanks guys for you willingness to take the time to educate, for those who care to listen. If it was not for those individuals who want to be informed, this form would only exist as chatty bunk .
John H
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NogginBoink
Dallas, TX
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welove2drive wrote:As with any connection of this kind it is always better to use the -, or ground side. This prevents the possability of a short if any of the cables touch anything grounded.
A disconnected positive terminal would also prevent a short in such an instance.
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Arn
Ottawa Valley, Ontario, Canada
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Joined: 06/09/2004
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Just purchased a blade type disconnect & the instructions state to connect to negative side & not for marine use.
Arn
1958 Me
1963 Her
Sometimes a 2002 granddaughter & 1 or 2 friends
Sometimes a 2004 black lab
2010 Rockwood Ultra-Lite Rear Lounge 2604SS
2005 F-150 XLT Super Crew 4x4, 5.4 Triton, 3.73 LS, tow package, Prodigy Controller
Life is good my friends, life is good
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welove2drive
Southwestern Illinois
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If you were to disconnect the postive cable as you say and wanted to plug the trailer in for lights or anything if the positive cable was resting on the frame or something metal attached to the frame the charging system would be shorted to ground. Not the case if the ground cable is the one that is disconnected.
NogginBoink wrote:welove2drive wrote:As with any connection of this kind it is always better to use the -, or ground side. This prevents the possability of a short if any of the cables touch anything grounded.
A disconnected positive terminal would also prevent a short in such an instance.
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