# Switch the Negative? Fuse the Negative?

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e-doggies
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Joined: 12/30/2007
Points: 280

In a simple DC circuit consisting of a battery, a fuse, a switch, and a load, does it matter if the switch or fuse are on the positive side of the battery, or the negative?

Electrons flow from negative to positive, right? But I usually see the fuse and switch on the positive side of the battery.

Would someone set me right on this. It would solve a wiring problem if I could put the main battery cut-off switch between the battery and the load on the negative side.

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antiscab
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Joined: 07/07/2007
Points: 1585
Re: Switch the Negative? Fuse the Negative?

for a circuit that simple,
it makes no difference where in the cricuit the fuse or the switch is.

Matt

__________________

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst replacement TC Charger
conversion
Spent so far: \$5800 + \$7000 + \$1720 + \$960 + \$320 + \$720 + \$140 + \$600
Cost to do it again: \$2500 + \$5600 + \$1720 + \$960 + \$320 + \$720 + \$140 + \$600
Cost for a Petrol bike:\$6000 + + \$1440 + \$6000 + \$800 + \$1400 + \$3200 servicing
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chas_stevenson
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Joined: 12/06/2006
Points: 1309
Re: Switch the Negative? Fuse the Negative?

I would like to clarify the statement made by Matt. The statement is correct however, the switch should be nearest the battery then the fuse in the same wire. The reason the switch should be first is so when changing the fuse the switch can be turned off thereby disconnecting that side of the battery from the fuse. Just a safety thing. I would also add the use of a frame ground, plus or minus, would require the switch and fuse be on the opposite pole of the battery from the frame ground, again a safety issue. Here are some illustrations;

Grandpa Chas S.

e-doggies
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Joined: 12/30/2007
Points: 280
Re: Switch the Negative? Fuse the Negative?

Thanks Matt and Grandpa. I didn't think it should make a difference which side the switch is on. I never considered the position of the fuse relative to the switch though.

Specifically, I have (4) 12V AGM's in series connected to a 48V contoller. Somewhere in there, a 100A Battery Disconnect Switch.

I'm adding a PakTrakr and do not want the current drain on just one (Batt#1) battery 24/7. So I am looking for a way to turn the PT On and Off easily. Easiest option I can see is to run the negative (black) lead from the PT Sensor through my main disconnect, instead of directly to the negative terminal on Batt#1. When I pull-out the key and walk away, everything will be off (I won't have to remember to throw a separate switch). But, as Ken Hall pointed out to me, I will lose accumulated data every time I power off the PT. That's not a concern to me, since I'm not logging data.

I considered the frame ground, and since nothing is grounded to the frame anywhere, I think putting the main power switch on the negatve side will be safe enough.

Harlow

antiscab
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Joined: 07/07/2007
Points: 1585
Re: Switch the Negative? Fuse the Negative?

gday Harlow,

switching the negative side of the modules for the paktrakr is exactly how i turn mine off on my emax.

Chas,
thanks for the correction.
i keep forgetting that point, on the battery packs i tend to wire, i put one or more contactors in the middle of the pack depending on voltage. so correct placement of the fuse(s) isn't something i have to worry about very often.

Matt

__________________

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst replacement TC Charger
conversion
Spent so far: \$5800 + \$7000 + \$1720 + \$960 + \$320 + \$720 + \$140 + \$600
Cost to do it again: \$2500 + \$5600 + \$1720 + \$960 + \$320 + \$720 + \$140 + \$600
Cost for a Petrol bike:\$6000 + + \$1440 + \$6000 + \$800 + \$1400 + \$3200 servicing
Total spent: \$17260
Total to do again: \$12560
Total to have used a petrol bike: \$18840
Total distance travelled so far: 79'120km

ruprek
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Joined: 07/29/2007
Points: 126
Re: Switch the Negative? Fuse the Negative?

I don't know if this enters into the equation, but I know that for a brushless controller, Kelly's anyway, the last thing you want to do (literally) is disconnect the ground. If I glossed over something, mea culpa.

e-doggies
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Joined: 12/30/2007
Points: 280
Re: Switch the Negative? Fuse the Negative?

ruprek,

So if you leave the positive connected, and disconnect the negative from the battery to a Kelly brushless controller, it's bad? What happens?

colin9876
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Joined: 10/23/2008
Points: 289
Re: Switch the Negative? Fuse the Negative?

Can anyone clarify this 'connected to the ground' thing.
Neither of my wires from my battery or to the motor are connected to the frame etc? With rubber tyres this wouldnt be connected to the ground anyway?

chas_stevenson
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Joined: 12/06/2006
Points: 1309
Re: Switch the Negative? Fuse the Negative?

Frame grounding is not repeat NOT needed on a bike or scooter. This is something normally done on automobiles. There is no requirement to ground the frame on a bike or scooter, the only reason I said anything about it is, I am never sure about every vehicle out there. Maybe some manufacture will use the frame as ground. If this happens then you have to use the ungrounded side as you power on and off. If the vehicle in question do not use the frame as ground then don't worry about.

One example I can think of on a bike is the little generators used to power lights. The ones that are spring loaded and place a roller on the side of a tire to generate the power as you peddle. Have you ever looked at these closely? There is one wire going to the lights and the bike frame is used as the second wire to complete the circuit. This is one time when the frame is used as a ground on a bike.

Grandpa Chas S.

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