How many volts are required to crank a 4.0?

I want to install an alarm circuit that will sound when my battery gets below the engine starting voltage. I use my outlets a lot with my truck off and have drained the battery a little low before. My question is does anyone have a good idea what voltage to set it to trip at?

 

Its not so much voltage you need you need AMPS to do the work. As for starting its around 80 to 150 amps( depends on engine temp) at 12.4 volts. Of course the lower the voltage the higher the amps have to go to make up the difference.

I will give you a better idea use a second battery problem solved.

Automotive SLI batteries are usually lead-acid type, and are made of six galvanic cells in series to provide a 12 volt system. Each cell provides 2.1 volts for a total of 12.6 volt at full charge.

 

A fully charged battery is 12.2 volts I believe, and a fully discharged battery is 10.5. It is never a good idea to run a battery down past half way, and that is especially true of a starting battery. Deep cycles can take more abuse. I would set the trigger around 11.5 volts. If that doesn't provide enough power for your other needs, you'll need to add a deep cycle on an isolated circuit.

 

i know some remote starters have that feature built in where they will start the car automaticly when battery gets drained....

 

sounds like second battery time.

 

Battery is pretty weak at 12.2 volts a fully charged battery is 12.7 as the voltage drops the current climbs. There are any number of voltage cut offs on the market generally used on stuff that has a lot parasitic drains like cop cars ambos etc.

 

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sounds like a second deep cycle battery is what I need. I wasn't looking to add a battery in my bed but it would be the best route I guess. Has anyone ever used a Odyssey battery. I had one on a motorcycle I built but only had it for a month, so I never got to see how it performed. I hear they are supposed to be the best, and they are half the size of a stock battery. Maybe if I run two 12 volt odysseys parallel that will give me twice the amperage and a longer lasting 12 volts, and will still fit under the hood...

 

unless you had the amperage to keep up.

power is voltage multiplied by current.

 

No, 12V is just the nominal voltage. Mainah is correct that a fully charged battery is 12.7V. It depends on the battery though. An older battery may never reach 12.7. When the vehicle is running most everything is operating on 14 V. When operating on just the battery, the voltage is another way of looking at the specific gravity. Both decrease as the stored charged is used. Most all components work off a wide range of voltages.

 

The Sears Platinum is a rebadged Odyssey. Very good battery. You need a deep cycle for the second battery, not a starting battery. They are not the same. I agree that a second battery is a good idea. Determine your demand and then size it accordingly. Some people also attach a solar charger to their aux. battery and extend the operating time even farther.

Here's a good website that I have bookmarked for my own use:
http://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html

 

I see it's been mentioned before. You could have a fully charged batter at 12.6V with 50 CCA, and your truck will not start. Aqt the same time you could have a battery at 10.5V with 600CCA, and your truck will start. With 12v, and 200cca, it will be very slow cranking, but should start, baring your not in cold temperatures.

 

As stated above by maineah. I think it was called a battery buddy.It cut the power when battery was getting low.. Its set to have enough power left to start vehicle.

 

support

 

The only problem with that is at 10.5 volts you do not have 600 CCA you have a very dead battery. The rated CCA is only at 12.7 and falls like a rock as the voltage drops. You could have a 1000 amp battery and at 10 volts it won't crank or lights the lights. A good battery pushed beyond it's rated amperage may not start an engine but just about any thing out there now in a decent state of tune will start easily. Starting batteries have a lot of short duration amperage but not much reserve it is what they were intended for so they don't do well with the likes of inverters that draw heavy current over a longer time span the inverter full load is going to draw 30+ amps a start battery won't be able to sustain that for very long. If you need to run the inverter a battery isolator and a deep cycle battery will be your only way out.

 

Can I hook the Deep cycle battery up so my alternator will charge it while my engine is running?

 

Sure you can. That's how the batteries in travel trailers charge while you drive. You can probably google around and find wiring diagrams. It's easy. You will need it "isolated" though. There is more than one way to do that. I use a relay triggered off an acc wire. You can buy actual isolators too. I've used both schemes in the past.

 

Not quite so simple as all batteries have some internal resistance.
If a new battery has an internal resistance of 5 milli-ohms, and all the connections back to the starter add another 5 milli-ohms, then at 250 amps, the voltage drop is 250 amps x .01 ohms = 2.5 volts. This is common to have only 10 volts at the starter and it will turn over just fine. As the battery ages, sulfates and corrodes internally; this resistance goes up, and the voltage at the starter drops (which provides less current and less/slower starting. There are other factors as well:
Cold weather will also increase the internal resistance and reduce the capacity of the battery.
When a battery is rated at 550 CCA or 550 Cold Cranking Amps, it indicates that the battery can supply 550 amps at 0 degF, and the voltage will be 7.2 volts or higher.
This means when the internal voltage is at 12.5 volts (fully charged at 0 degF) -7.2 = 5.3 Volts at 550 amps = 5.3 /550 = 10 milli-ohms.
Note that cold engines are more difficult to crank over due to tighter components and thicker oil. The battery also loses about 50 - 60 % of its capacity. Clean an lower viscosity oils at the W rating (10W -30) will also alleviate the power required to start.

 

@jvalky, did you look at the last post date? May 8, 2012. How'd you even find this thread?