A *proper* battery isolator. *Critical tech info*
02-12-2011, 10:59 AM
#1
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Join Date: Dec 2010
Posts: 17
A *proper* battery isolator. *Critical tech info*
Ok so I've finished working on the isolator circuit and as an electrician I gotta say it's completely ideal for an automotive system because unlike a contactor (isolator from ebay for 200 amps) or a solid state (canadian tire for 90 amps)
this draws ZERO from the battery when not in use and is far more robust.
I drive an 89 Jetta Mk2 TurboDiesel so I have glow plugs to warm up.
With a heavy duty isolator the contactor is wired to ignition so when you turn the key partway (either to start the gas engine, or to warm the glow plugs for diesel) this will kick in the rear battery and it will not be isolated from the starting circuit! This is the unit i'm talking about: a 200amp heavy duty isolator.
http://gadgetpro.stores.yahoo.net/efxmucore200.html
An electronic (solid state) isolator is wired to the alternator so will not connect the batteries until after starting but they are only good for 90amps (which means 45amps per battery, not enough to keep up with a real stereo system). Do not use these, they are pointless.
What I have done is purchase a timing relay. Like this one
http://www.canfieldconnector.com/products/electronic-timers/model-tmlt.htm?gclid=COeEg7qKg6cCFQPsKgodQV_ieA
but mine is simpler, instead of adjustments I simply connect a relay across two terminals to set the timing.
What happens is this:
I turn my key (to warm the glow plugs for ten seconds) and the relay gets power. It waits 17 seconds (my choice of timing) and then sends power to the contactor (first link above) which connects the batteries. By this time the car is running.
Why is this important?
Because if you allow your trunk battery to be included in the starting circuit it will send high current through its power feed, through your isolator, and into the starter along with the main engine battery. That means running 0 gauge unless you want a fire.
My car's stereo is powered from the rear battery, an optima blue top deep cycle. I only needed to run a #4 power wire to it because it will only draw a mild load while charging. Big savings, and way easier of a job.
Pictures on the way, but in summary remember you need to use #2 or larger wire for your front power circuit (especially off a 300amp alternator like mine 0 gauge is suggested). and you absolutely must avoid using two batteries to start the car. The voltages will be off, as will charge levels and they will start to see circulating currents between them in the seconds before your car starts. These currents will oppose the starting current and cause extra heat.
Why stress the system? Design it right in the first place.
any questions?
this draws ZERO from the battery when not in use and is far more robust.
I drive an 89 Jetta Mk2 TurboDiesel so I have glow plugs to warm up.
With a heavy duty isolator the contactor is wired to ignition so when you turn the key partway (either to start the gas engine, or to warm the glow plugs for diesel) this will kick in the rear battery and it will not be isolated from the starting circuit! This is the unit i'm talking about: a 200amp heavy duty isolator.
http://gadgetpro.stores.yahoo.net/efxmucore200.html
An electronic (solid state) isolator is wired to the alternator so will not connect the batteries until after starting but they are only good for 90amps (which means 45amps per battery, not enough to keep up with a real stereo system). Do not use these, they are pointless.
What I have done is purchase a timing relay. Like this one
http://www.canfieldconnector.com/products/electronic-timers/model-tmlt.htm?gclid=COeEg7qKg6cCFQPsKgodQV_ieA
but mine is simpler, instead of adjustments I simply connect a relay across two terminals to set the timing.
What happens is this:
I turn my key (to warm the glow plugs for ten seconds) and the relay gets power. It waits 17 seconds (my choice of timing) and then sends power to the contactor (first link above) which connects the batteries. By this time the car is running.
Why is this important?
Because if you allow your trunk battery to be included in the starting circuit it will send high current through its power feed, through your isolator, and into the starter along with the main engine battery. That means running 0 gauge unless you want a fire.
My car's stereo is powered from the rear battery, an optima blue top deep cycle. I only needed to run a #4 power wire to it because it will only draw a mild load while charging. Big savings, and way easier of a job.
Pictures on the way, but in summary remember you need to use #2 or larger wire for your front power circuit (especially off a 300amp alternator like mine 0 gauge is suggested). and you absolutely must avoid using two batteries to start the car. The voltages will be off, as will charge levels and they will start to see circulating currents between them in the seconds before your car starts. These currents will oppose the starting current and cause extra heat.
Why stress the system? Design it right in the first place.
any questions?
02-12-2011, 06:00 PM
#3
If you have a 300amp alternator and you are running only a 4 gauge line front to back, you have a inherent wiring problem in your system design. I find many flaws with what you are recommending to others and at the same time there is indeed some fact behind it.
A proper system would have identical batteries front and rear. A proper system would also use the appropriate guage wire front to rear for power and ground. If you have a 300amp alternator and a 4 gauge line running to the rear to charge the battery, you must have a fairly small system and too large of an alternator. Unless you are running a snowplow or a million jiggawatts of power on offroad light, all of which would make a Jetta a one in a million kind of vehicle.
Not trying to start something, I commend you that you have looked at a issue and developed a plan for it but the rest of the plan needs the same attention.
A proper system would have identical batteries front and rear. A proper system would also use the appropriate guage wire front to rear for power and ground. If you have a 300amp alternator and a 4 gauge line running to the rear to charge the battery, you must have a fairly small system and too large of an alternator. Unless you are running a snowplow or a million jiggawatts of power on offroad light, all of which would make a Jetta a one in a million kind of vehicle.
Not trying to start something, I commend you that you have looked at a issue and developed a plan for it but the rest of the plan needs the same attention.
02-14-2011, 07:27 AM
#4
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Join Date: Dec 2010
Posts: 17
If you have a 300amp alternator and you are running only a 4 gauge line front to back, you have a inherent wiring problem in your system design. I find many flaws with what you are recommending to others and at the same time there is indeed some fact behind it.
A proper system would have identical batteries front and rear. A proper system would also use the appropriate guage wire front to rear for power and ground. If you have a 300amp alternator and a 4 gauge line running to the rear to charge the battery, you must have a fairly small system and too large of an alternator. Unless you are running a snowplow or a million jiggawatts of power on offroad light, all of which would make a Jetta a one in a million kind of vehicle.
Not trying to start something, I commend you that you have looked at a issue and developed a plan for it but the rest of the plan needs the same attention.
A proper system would have identical batteries front and rear. A proper system would also use the appropriate guage wire front to rear for power and ground. If you have a 300amp alternator and a 4 gauge line running to the rear to charge the battery, you must have a fairly small system and too large of an alternator. Unless you are running a snowplow or a million jiggawatts of power on offroad light, all of which would make a Jetta a one in a million kind of vehicle.
Not trying to start something, I commend you that you have looked at a issue and developed a plan for it but the rest of the plan needs the same attention.
Two batteries only need to be the same if interconnected when not actively charging. The second the alternator comes into play the batteries will not equalize charge which is the reason identical batteries are usually sought after. The contactor and relay isolation circuit make that issue disappear.
Also my wire gauge size is totally correct, you missed the fact that the stereo is powered from the rear battery off 0 gauge power wire. The whole point to rear batteries is that you only need a small wire to charge them. The system will never draw high amps from the front setup, and when the car is off, the isolator contactor actually separates them mechanically so that cant happen.
My system runs relatively moderate power, but is tuned and extreme quality.
This setup is electrically safe (far more so than most car audio designs I've seen). The wire sizes are actually overkill.
Its important to understand the role of isolators and switching, and how electricity works.
And no, I will not be selling these. I will however be posting my circuit diagram and photos of the system on here so anyone can copy them and make their own. Free service
02-14-2011, 07:30 AM
#5
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Join Date: Dec 2010
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also, the best twin battery systems are set up so that the starting battery is a high cranking power battery, and the second battery is a high reserve capacity deep cycle. The second battery is isolated so it cannot be used to start the car. This makes its design ideal for car stereo applications.
My next step is to install switched voltage meters in my dash, so I can check the health of both batteries from the drivers seat and gauge available power.
My next step is to install switched voltage meters in my dash, so I can check the health of both batteries from the drivers seat and gauge available power.
02-14-2011, 08:20 AM
#6
I'm having a hard time understanding..
Your amps use 1/0 awg from the 2nd battery, so when the amp asks for power, the 2nd battery gives it.
Now the 2nd battery is down on voltage, the 1st battery sends the juice to the 2nd.
But, heres where I'm lost.
If you're amps actually need the full current from the 1/0 and 2nd battery, how does a 4 awg much longer wire recharge the 2nd batt, when a 1/0 sized current has been taken?
Seems like the 2nd battery wouldn't get fully charged if running the amps hard
What am I missing?
Your amps use 1/0 awg from the 2nd battery, so when the amp asks for power, the 2nd battery gives it.
Now the 2nd battery is down on voltage, the 1st battery sends the juice to the 2nd.
But, heres where I'm lost.
If you're amps actually need the full current from the 1/0 and 2nd battery, how does a 4 awg much longer wire recharge the 2nd batt, when a 1/0 sized current has been taken?
Seems like the 2nd battery wouldn't get fully charged if running the amps hard
What am I missing?
Last edited by SOULMUSIC; 02-14-2011 at 08:23 AM.
02-14-2011, 04:39 PM
#8
Speaking as an electrician????? how on earth do you figure that a battery runs the stereo.....
My F350 diesel has stock dual batteries, no isolator or anything and has a massive current draw off of it compliments of a monster snowplow. Explain how your theory has not resulted in my vehicle dying.
My F350 diesel has stock dual batteries, no isolator or anything and has a massive current draw off of it compliments of a monster snowplow. Explain how your theory has not resulted in my vehicle dying.
Last edited by MR2NR; 02-14-2011 at 05:31 PM.
02-14-2011, 08:54 PM
#9
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Join Date: Dec 2010
Posts: 17
Redundant is perfectly fine, redundant is safe and max power capacity.
As for your truck its a totally different system. Those batteries are for the trucks built in electronics not anything specific. No need for isolation.
and father yuli not a single part of this is wrong
SOULMUSIC:
here i'll try to clarify.
The isolating is extremely important, because you do not want current from the rear battery used to help start the car, that would be HIGH current and require running 0 gauge all the way through the car. also very dangerous for fires if there were ever a short circuit.
Also isolating them so completely protects the two batteries from damaging each other because they will have unequal charges (unlike buddys truck setup which is totally different and not suitable for this application to begin with). The two batteries also have different charge characteristics and voltage outputs because of construction.
As for the sizing...
In high powered stereo generally it will never be drained right to death. the extra battery is just to supply a buffer of easily accessible energy for the system, and to allow you to run it with the engine off without risking your main battery, so the car will always start.
You can tell how much its safe to use with the engine off by looking at the reserve capacity and doing some tricky math.
When the battery needs charging, the alternator takes care of it.. it will not be feeding hundreds of amps to the rear battery to charge, a battery can only take charge at a certain rate, which is much lower.. it should never exceed 40 amps or so at 13 volts. This is more than handled by the #4 wire.
The reason people run heavy wire to the back is because they are not using dual batteries properly isolated, they are running their stereo off their alternator and main battery directly which does not make sense when you can put the power source right by the amps and run 3 feet of 1/0 wire instead of 15 feet.
Electrically speaking what I have done (especially with the capacitor, which isnt really needed but is kind of cool to have) is overkill.
I'm not about being a cheapass, I am exercising my brain here and using a lot of advanced electrical/electronics understanding to make this more interesting.
Ignition switching, resistance timing circuits, multiple voltage sources, parallel grounds, high power generation.. its all just cool practice.
It would have been simpler just to run a single #2 to the back, throw a cap on it, and run off the alternator and high quality engine battery.
But for an electrician with nothing else to do and a creative mind that just isnt "redundant" enough. I will never see a voltage drop on any other electronics, never see my lights dim even at max power, and I can run all afternoon with my stereo then it will charge up in no time. It's just fantastic.
It's not however, the cheapest way to do it... and people cut so many corners they get pissy when someone does it right.
Never, ever, ever hook up a spare battery without an isolator... unless in the engine bay of a large truck. Almost everything a truck does with power is with the engine running. Totally different purpose.
As for your truck its a totally different system. Those batteries are for the trucks built in electronics not anything specific. No need for isolation.
and father yuli not a single part of this is wrong
SOULMUSIC:
here i'll try to clarify.
The isolating is extremely important, because you do not want current from the rear battery used to help start the car, that would be HIGH current and require running 0 gauge all the way through the car. also very dangerous for fires if there were ever a short circuit.
Also isolating them so completely protects the two batteries from damaging each other because they will have unequal charges (unlike buddys truck setup which is totally different and not suitable for this application to begin with). The two batteries also have different charge characteristics and voltage outputs because of construction.
As for the sizing...
In high powered stereo generally it will never be drained right to death. the extra battery is just to supply a buffer of easily accessible energy for the system, and to allow you to run it with the engine off without risking your main battery, so the car will always start.
You can tell how much its safe to use with the engine off by looking at the reserve capacity and doing some tricky math.
When the battery needs charging, the alternator takes care of it.. it will not be feeding hundreds of amps to the rear battery to charge, a battery can only take charge at a certain rate, which is much lower.. it should never exceed 40 amps or so at 13 volts. This is more than handled by the #4 wire.
The reason people run heavy wire to the back is because they are not using dual batteries properly isolated, they are running their stereo off their alternator and main battery directly which does not make sense when you can put the power source right by the amps and run 3 feet of 1/0 wire instead of 15 feet.
Electrically speaking what I have done (especially with the capacitor, which isnt really needed but is kind of cool to have) is overkill.
I'm not about being a cheapass, I am exercising my brain here and using a lot of advanced electrical/electronics understanding to make this more interesting.
Ignition switching, resistance timing circuits, multiple voltage sources, parallel grounds, high power generation.. its all just cool practice.
It would have been simpler just to run a single #2 to the back, throw a cap on it, and run off the alternator and high quality engine battery.
But for an electrician with nothing else to do and a creative mind that just isnt "redundant" enough. I will never see a voltage drop on any other electronics, never see my lights dim even at max power, and I can run all afternoon with my stereo then it will charge up in no time. It's just fantastic.
It's not however, the cheapest way to do it... and people cut so many corners they get pissy when someone does it right.
Never, ever, ever hook up a spare battery without an isolator... unless in the engine bay of a large truck. Almost everything a truck does with power is with the engine running. Totally different purpose.
