battery seperator + mosfet PLZ help

Mcnovy · 07-19-2005, 06:42 AM

Hello

i am looking for some schematics for at battery separator using fet's

why fet's?
diode's give me the little 0,6 volt drop, shottky about 0,2 v but thats still to much..!
so does anyone know of any schematics..?

and that is for controlling an exktra battery in the thrunk.

Thanks

babazoid · 07-19-2005, 11:47 PM

Quote: Originally Posted by Mcnovy

Hello

i am looking for some schematics for at battery separator using fet's

why fet's?
diode's give me the little 0,6 volt drop, shottky about 0,2 v but thats still to much..!
so does anyone know of any schematics..?

and that is for controlling an exktra battery in the thrunk.

Thanks

Why don't you just use a relay? Seriously, they are like 3$.

I've been using this setup for a month now, it works great. Battery charges when car is on, and as soon as I turn off the car the battery is cut from the car's power. If I drain the back battery (not possible as my M1-ATX shuts down if the power supply reaches 11v) then there is no effect on the car's power.

Later
Mark

Mcnovy · 07-20-2005, 10:23 AM

Quote: Originally Posted by babazoid

Why don't you just use a relay?

well, if my backup battery gets drained to lets say, 10 volts..
that would mean that, as soon as i turn on my car, and the relay shuts, then my altenattor and my starter battery will do as much as they can do charge the drained backup battery.
so if i turn of my car after 2 min. and the relay open, then the starter battery have drained itself to charge the the backup battery.
so the two battery's then got the same voltage, but the voltage would be something like 11 volt instead of 12,6 v that the starter battery should have.
i think its here i've also read it
http://www.surepower.com/pdf/ebr_int.pdf

in you setup and your car its would probalby work fine in the long run.
but my car have a minimum cranking voltage, and that is 12,3 volts i mean, if the voltage drops under, it want start..!

babazoid · 07-20-2005, 03:24 PM

Quote: Originally Posted by Mcnovy

well, if my backup battery gets drained to lets say, 10 volts..
that would mean that, as soon as i turn on my car, and the relay shuts, then my altenattor and my starter battery will do as much as they can do charge the drained backup battery.
so if i turn of my car after 2 min. and the relay open, then the starter battery have drained itself to charge the the backup battery.
so the two battery's then got the same voltage, but the voltage would be something like 11 volt instead of 12,6 v that the starter battery should have.
i think its here i've also read it
http://www.surepower.com/pdf/ebr_int.pdf

in you setup and your car its would probalby work fine in the long run.
but my car have a minimum cranking voltage, and that is 12,3 volts i mean, if the voltage drops under, it want start..!

Yeah, I guess I just don't see that being a problem because of the M1-ATX's 11v shutdown. My tank battery really will only ever power the PC for a few minutes (during a gas station stop for example).

Good luck!

BOWDOWN · 07-21-2005, 10:03 AM

Do you already have a FET-based isolator or do you already have it? In any case, here is one with schematic.

It is the DuoCharge from Balmer

Digital Duo Charge (DDC-12/24)

Say “so long” to switches. Put your isolator on “ice”.
The Digital Duo Charge delivers a smarter, safer and
faster way to care for your batteries.

Four built-in battery programs – Deep Cycle Flooded,
AGM, Gel and Standard Flooded – safely maintain
two battery types from the same charging source!
Unique FET-based control virtually eliminates voltage
drop while delivering up to 30 amps, so your batteries
reach full charge quickly. Should greater charging
power be required, the Duo Charge can be used to
control a separate solenoid.

Battery temperature sensing (with optional sensor)
adds even greater safety. Minimal “sleep” draw of
14mA when house voltage is less than 13V. Working
draw is just 25mA. Epoxy potted circuitry in a durable
anodized aluminum heat sink. Measures 4.6"L x 3.2W
x 1.5"W. One year limited warranty.

*Requires Battery Temp. Sensor (MC-TS-B).

They have a schematic @ http://balmar.net/page20-Duocharge.html. They also were supposed to release the Duo-Charge II, a fancier version of the first, in the Spring.

evandude · 07-21-2005, 10:19 AM

why don't you just BUY a battery isolator? look at them, they are one giant heat sink. even if you built one yourself, it would be a big pain to heat sink it properly... not to mention, screwing around with the currents going through your car electrical system, you'll probably have at least one prototype go up in flames

Mcnovy · 07-23-2005, 09:12 AM

i was hoping for a schematic with components, fets resistors etc.
not just a how to wire the thing.!

hmm, here in denmark, the relay based isolators are about 250$, and they are the cheap ones, thats why i am hoping to make one my one.!

checksum · 03-27-2006, 01:02 AM

Why are you using 2 batteries? Is this because you want more power output? Or to keep the battery life longer?

84RegalRider · 03-31-2006, 01:30 PM

2 alts are better then 1

davesaudio2 · 04-03-2006, 03:27 PM

How much current do you expect to pass through these mosfets?

Mcnovy · 06-09-2006, 05:08 PM

Quote: Originally Posted by checksum

Why are you using 2 batteries? Is this because you want more power output? Or to keep the battery life longer?

i want my amp and carputer to be mounted to the sec. battery, so that i i forget to turn of the music by mistake.. or an error accurs, then my main battery will be fully charged, and i will not get engine start trouble

Quote: Originally Posted by 84RegalRider

2 alts are better then 1

Yeah.. that would be great.. although.. my alt. is 150 amps.. so that should do it..!
and i do not have the space for a sec. alt

Quote: Originally Posted by davesaudio2

How much current do you expect to pass through these mosfets?

well.. 200 amps at least..!

i know some uses diodes.. but that makes 0,6 volts of loss.
some uses relays.. but hten the power will go both ways..!

and i am pretty shure that it is possible to make it with fets, so there would be no voltage drop