Measuring +12v (was ADC and the BSII)
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> Is the stamp communicating with the MAX186? Like when you say 0 or 4.095V
> does the ADCin variable have 0 or 4095 in it? When you connect the input
to
While we're on the topic of ADC ... is it possible for me to measure a
voltage outside of the range of the +5 rail? I'd like to measure the
battery voltage in my car.
-- Mitch
> does the ADCin variable have 0 or 4095 in it? When you connect the input
to
While we're on the topic of ADC ... is it possible for me to measure a
voltage outside of the range of the +5 rail? I'd like to measure the
battery voltage in my car.
-- Mitch
Comments
Vout = (R1/(R1 + R2)) * Vin
Vin
^^^^^----Vout
^^^^^
GRND
12V R2 Vout R1 GRND
The idea is to make Vout the near the max of your ADC ~5V. Remember a
battery can float as high as 15V
Some rough rules of thumb for lead acid batteries: 14.2v fully charged no
load, 13.8v fully charged small load ~1amp, 12.6v fully charged heavy load
~20amp. 11.2v and less is a "dead" battery. A healthy car battery should
sustain a voltage above 10v under 400amps for 10secs.
Original Message
From: "Mitchell D. Miller" <mdmiller2@h...>
To: <basicstamps@egroups.com>
Sent: Saturday, July 29, 2000 11:41 PM
Subject: Re: [noparse][[/noparse]basicstamps] Measuring +12v (was ADC and the BSII)
> > Is the stamp communicating with the MAX186? Like when you say 0 or
4.095V
> > does the ADCin variable have 0 or 4095 in it? When you connect the input
> to
>
> While we're on the topic of ADC ... is it possible for me to measure a
> voltage outside of the range of the +5 rail? I'd like to measure the
> battery voltage in my car.
>
> -- Mitch
> sustain a voltage above 10v under 400amps for 10secs.
How long should I be able to draw 4A and still start the car afterward?
Been looking at those electric coolers, and have considered controlling it
so that it doesn't completely run my car battery down!
-- Mitch
It all depends on the amp-hours the car battery is rated for, the outside
air temp, the condition (age) of the electrolyte. An electric cooler can
kill a highway trucks' battery system in 6 hours (800 amp-hours +).
Automotive batteries are not deep cycle, they are designed to give a huge
current for a short time and then be recharged by the alternator.
Another thought is: will the electric cooler like being controlled? I
imagine they use the peltier (sp?) effect. Will the thermo-electric cooler
like PWM?
Maybe a safer (no dead battery) solution might be to have a deep cycle golf
cart battery just for the cooler? Isolate the golf cart battery with a diode
circuit that will allow the alternator to charge it. But what would the fun
be in that [noparse]:)[/noparse]
Please let us know how your project comes along.
> imagine they use the peltier (sp?) effect. Will the thermo-electric cooler
> like PWM?
The stuff I'd seen indicates peltier devices work fine with PWM. I've not
opened up a commercial unit, but suspect they simply turn the unit on until
a certain temperature is reached, then shut it off. I'd like to modify it
to actually maintain the temperature by using PWM.
> Maybe a safer (no dead battery) solution might be to have a deep cycle
golf
> cart battery just for the cooler? Isolate the golf cart battery with a
diode
> circuit that will allow the alternator to charge it.
I thought of doing this, too. Not sure of some of the mechanics involved.
If a diode has a .6v drop, then that means that it'll never even see the
full charging potential, right? Also, how much current will it draw after
powering the cooler all night and now you start the car to charge it?
-- Mitch
> If a diode has a .6v drop, then that means that it'll never even see the
full charging potential, right?
Thats right, if you go to an RV center they have a diode block that has a
voltage sense connector for the alternator that figures that all out for
you. It has hook up and forget instructions.
>Also, how much current will it draw after
> powering the cooler all night and now you start the car to charge it?
Alternators have a current limiting circuit in them. A 60 amp alt will not
do 65 amps. There should be no problem with charging the deep cycle while
driving. Large marine alternators make great emergency arc welders.
Remember that if your main battery is in good condition it will take very
little current from the alt. Your lights and accesories in the car are
always run by the alt when the engine is running. Visit your local RV
dealer and ask about isolators.
>The stuff I'd seen indicates peltier devices work fine with PWM
Thats great!
Good luck, and keep us updated.
Matthew