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battery disconnect switch in car


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oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: September 22, 2014 at 5:24 AM / IP Logged  
50mA IMO is a bit high.
I had an Alpine that drained ~120mA and that was only a problem after 3-4 days, and that's with a smallish battery (~40AH). My other drains are under 10mA.
Maybe the battery is old or has lost capacity. That's often the cause of such problems.
Of course draining a battery that quick is a problem. I'd steel the vehicles after it's been sitting for a day...
Of course now I know it'll have an isolator I can steel it anytime.
I bond to chassis because my vehicles are either of monocoque design with reasonable rail gauges here & there, else proper chassis frames.
Even if monocoque did involve heavy metal gauges, their electrical bonding should be quite good so it's a matter of having a big enough connection area.   
I maintain that chassis and bodies conduct better than cables, but I have heard stories where apparently there is insufficient bonding & conduction due to insufficient spot welds or excessive corrosion. And of course non-metallic panels and glues will not conduct!
Some claim a mere 16G panel is insufficient for cranking and big amplifier etc currents but they don't seem to take panel width into account. Then again, some steels only have 6% the electrical conductivity of copper.
The simple test is to measure voltage drops during operation or cranking. If battery- to starter case is (say) only 1V, fine. If it's too high, do various measurements to see where the drop occurs.
catback 
Silver - Posts: 703
Silver spacespace
Joined: August 13, 2002
Location: Canada
Posted: September 22, 2014 at 9:42 AM / IP Logged  
If your uncle installs a battery disconnect to kill parasitic draws, there goes his gps tracker.
As for needing larger cable than factory, it's almost a requirement because of the much longer run - battery to switch and back.
If the only drain found is a gps tracker, he should have his battery tested they do go bad on weekend fair weather drivers as commonly if not more commonly than daily drivers.
pv13 
Copper - Posts: 154
Copper spacespace
Joined: April 11, 2005
Location: United States
Posted: September 22, 2014 at 1:04 PM / IP Logged  
This chevelle has been a project car for the past two and a half years. He has replaced the floor, but this car sat in western Washington state for many years, so there is no telling how much rust is hiding until he takes it apart. That is what worries me about the reliability of his electrical connections, especially further back in the vehicle.
Thank you all for your help and advice. If he still wants the switch, I'll convince him to keep it next to the battery. But he needs to find the drain. The problem is that I don't have a Digital multimeter with the capabilities to measure amp draw, and the local mechanics don't seem to know a great deal about testing voltage drops, resistance, or current. I'm pretty sure they initially claimed the gps tracker was at fault because that is the only accessory item installed in the car :).
So I will have to track down a mechanic who knows what they're doing.
Thanks again.
pv13 
Copper - Posts: 154
Copper spacespace
Joined: April 11, 2005
Location: United States
Posted: September 22, 2014 at 1:15 PM / IP Logged  
catback wrote:
If your uncle installs a battery disconnect to kill parasitic draws, there goes his gps tracker.
As for needing larger cable than factory, it's almost a requirement because of the much longer run - battery to switch and back.
If the only drain found is a gps tracker, he should have his battery tested they do go bad on weekend fair weather drivers as commonly if not more commonly than daily drivers.
Thanks for your input. Yeah, the whole point of the gps tracker is to constantly track the vehicle. But if he is taking off his negative and removing power from the tracker, it no longer functions. I have explained this to him several times :)
He replaced the battery, alternator, external voltage regulator, and corresponding cables, but still had a drain on the battery.
He needs to find a reliable mechanic who truly knows how to test vehicle electrical systems, and approach the problem analytically. Moving throughout the charging system measuring each part, cable, and connection, and determining whether they are "good" or not.
Thanks again
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: September 22, 2014 at 2:14 PM / IP Logged  
It ain't the tracker!
The units I install in the UK draw 3 milliamps except when sending and receiving on command.
Ween 
Platinum - Posts: 1,364
Platinum spacespace
Joined: August 01, 2004
Location: Illinois, United States
Posted: September 22, 2014 at 6:45 PM / IP Logged  
Is there a Menards or Home Depot near you? Both have multimeters, inexpensive units that will measure current.
Is the fuse box under the dash the original one (with glass fuses?) or has it been upgraded? The original only has four fuses and circuit breakers for the battery draw circuits, granted they do supply multiple items.The multimeter (in ammeter mode) connected in series on the battery or ground cable will show the current draw (50mA or so). Disconnect the tracker, check draw. Remove the fuses one at a time (for the battery supplied circuits) noting draw.
The courtesy/dome light circuit might be tricky as you'll need the door open to access the fuse box easier. If the bulbs are accessible, remove them first. ..then the fuse. When the current draw drops to minimal (10mA or less), the offending circuit should be identified. Battery circuits under the hood to disconnect would be the alternator, voltage regulator (if present), horn relay (may have key buzzer built in) assuming the draw hasn't been found.
Hope this helps.
Mark
pv13 
Copper - Posts: 154
Copper spacespace
Joined: April 11, 2005
Location: United States
Posted: September 22, 2014 at 7:05 PM / IP Logged  
Ween wrote:
Is there a Menards or Home Depot near you? Both have multimeters, inexpensive units that will measure current.
Is the fuse box under the dash the original one (with glass fuses?) or has it been upgraded? The original only has four fuses and circuit breakers for the battery draw circuits, granted they do supply multiple items.The multimeter (in ammeter mode) connected in series on the battery or ground cable will show the current draw (50mA or so). Disconnect the tracker, check draw. Remove the fuses one at a time (for the battery supplied circuits) noting draw.
The courtesy/dome light circuit might be tricky as you'll need the door open to access the fuse box easier. If the bulbs are accessible, remove them first. ..then the fuse. When the current draw drops to minimal (10mA or less), the offending circuit should be identified. Battery circuits under the hood to disconnect would be the alternator, voltage regulator (if present), horn relay (may have key buzzer built in) assuming the draw hasn't been found.
Hope this helps.
Mark
Thank you Mark. That does help. I told him to do a parasitic draw test in the past, but for some reason it never got done. He is going to be taking the car to his mechanic soon, and I will definitely pass on your suggestions. Thanks again
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: September 23, 2014 at 3:20 AM / IP Logged  
Of course if it is the tracker, put a switch on that & forget battery isolation.
And FWIW, when he has problems with the alternator or regulator, replace them with a modern alternator with integral regulator. They are far superior and overcome various problems with external regulators. I suggest 2-wire types ie with S&L "small" wires - namely Sense (which goes direct to the battery + terminal) and chargeLamp which goes to the dash charge lamp (and electric fuel pump and dual-battery isolator relays etc). You merely connect the L terminal to the original regulator's chargeLight output and run a (thin) wire from S to batt+ (which can be fused tho preferably the wire is thin enough to be its own fuse).
pv13 
Copper - Posts: 154
Copper spacespace
Joined: April 11, 2005
Location: United States
Posted: September 23, 2014 at 3:23 AM / IP Logged  
oldspark wrote:
Of course if it is the tracker, put a switch on that & forget battery isolation.
And FWIW, when he has problems with the alternator or regulator, replace them with a modern alternator with integral regulator. They are far superior and overcome various problems with external regulators. I suggest 2-wire types ie with S&L "small" wires - namely Sense (which goes direct to the battery + terminal) and chargeLamp which goes to the dash charge lamp (and electric fuel pump and dual-battery isolator relays etc). You merely connect the L terminal to the original regulator's chargeLight output and run a (thin) wire from S to batt+ (which can be fused tho preferably the wire is thin enough to be its own fuse).
That's a good point. I'll make sure to pass on the advice. Thanks
yellow_cake 
Copper - Posts: 178
Copper spacespace
Joined: December 01, 2011
Location: Saskatchewan, Canada
Posted: September 24, 2014 at 3:50 AM / IP Logged  
If you go on youtube, search for parasitic battery drain by EricTheCarGuy, that video in my opi nion is very helpfu.
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