Howdy,


There are a of couple newer devices that you might like
even more than the UC3906. Check out the UC3909
and BQ2031.

All zeners are not created equal! The 1N825 is a common
temperature compensated diode and it's uncommonly good.
Transfer standards built in the 1960's and 70's often
used zeners... and they were good enough by golly. The
venerated Fluke 335D used an ion implanted or burried
zener diode and it's still one of the most stable units
available.

Here's the deal, the battery voltage varies with temperature.
About minus 3 to minus 5 milivolts per degree C. Not very
stable! (However for temperatures between 5C to 35C it can be
safely ignored.)

Now if the circuit is exposed to the same ambient temperature
as the battery and your reference drifts about the same amount
and in the same direction as the battery, it can be only a good
thing.

A true zener has a negative temperature coefficient.
An avalanche diode has a positive temperature coefficient.
The cross over point between the two effects is around 5.6V
A common silicon rectifier diode has a negative 2 milivolts
per degree C coefficient.

It's not difficult to select a couple of parts that when
combined in series will produce the minus 5 milivolts per
degree C desired. A 6.8V zener in series with three 1N4001
running 1 milliamp of bias current is in the ball park.

Honest to god temperature compensated charging requires a
temperature sensor in the battery (thermistor usually)
but it's only needed where you're charging at a rate that
heats the battery or when charging over a very wide range
of ambient.


The above is just my opinion and all that jazz...


73,
Grumpy

Hello Jimmie,


I've used a relay to disconnect the auxilliary battery when either
the ignition is off or the auxilliary battery voltage is low ~11.5V.
There is a series diode and resistor in parallel with the relay
contacts to bring the auxilliary battery back up slowly when the
engine is running so the undervoltage lockout can reclose the relay
and not dump the discharged battery on the alternator.

The automotive "ice cube" relays are good for this I've seen some
rated as high as 80A.

Another refinement I did not try is a switch to override the undervoltage
lockout so I could jump the vehicle off the auxillary battery. Perhaps
the switch should be across the diode so the auxillary battery slowly
charges the main battery?


73,
Grumpy



JIMMIE wrote in news:b5cabbfd-f220-4c7e-9cef-
:

I want to add a couple of deep discharge type batteries to my truck
for camping but how do I intermix them with the normal auto battery
and charging system. I was thinking about getting a charger meant for
charging batteries from solar panels and connecting the solar panel
input to the generator. A 20A charger cost about $50USD .This would be
very reasonable if I knew it would work as expected.

Jimmie

Grumpy The Mule wrote in
:

A correction...

Another refinement I did not try is a switch to override the _ignition_
lockout so I could jump the vehicle off the auxillary battery. Perhaps
the switch should be across the diode so the auxillary battery slowly
charges the main battery?

"JIMMIE" wrote in message
...
I want to add a couple of deep discharge type batteries to my truck
for camping but how do I intermix them with the normal auto battery
and charging system. I was thinking about getting a charger meant for
charging batteries from solar panels and connecting the solar panel
input to the generator. A 20A charger cost about $50USD .This would be
very reasonable if I knew it would work as expected.

Jimmie

If the RV isn't being used all the time the Battery chemistry is less of an
issue. Deep cycles should be charged at roughly no more than 10 amps. and
floated at 13.2 v. But if it is being cycled, the float value is less of an
issue. You will need the long trip to insure it is up for the next stop.

If you are mounting the second battery under the hood, close to the charger,
then it is best to use NR 10 or 12 wire for the charge line to limit the
current and be able to disable the RV relay rather than leave it charging
every day on long commutes. You will need to check the water more often.

I didn't see my earlier post, again DON'T use a solar charge controller as
most regulate by shorting down the solar panel. If the system voltage is
normal, nothing happens. If it should go high for any reason then it would
simply burn out things.

On Nov 16, 4:21*pm, JIMMIE wrote:
I want to add a couple of deep discharge type batteries to my truck
for camping but how do I intermix them with the normal auto battery
and charging system. I was thinking about getting a charger meant for
charging batteries from solar panels and connecting the solar panel
input to the generator. A 20A charger cost about $50USD .This would be
very reasonable if I knew it would work as expected.

Jimmie

Hey jimmie:

TI makes a really sweet ic for charging batteries the UC3906. Is the
greatest IC since sliced bread for charging batteries. It took forever
to charge my deep cycle marine battery like a110AHr. A straight
charger it would take a week to charge 100% it's that last 15% that's
the toughest. The UC3906 charged my deep cycle marine battery to full
charge from dead in 10 hours. It's one of the greatest homebrew jobs
I've done. I used it to charge a 110AHr deep cycle marine battery for
my electric bike. I could ride 2 days on a single charge like $0.25
worth of electricty back and forth to work. 45 miles on a single
charge.

73 OM
n8zu

Agreed! I designed a DC UPS power supply for Harris using the
UC3906 to charge a 4Ahr gell cell for wireless pbx. The only
down side is it requires some head voltage for the regulator,
so it won't work well off a 12V vehicle system unless the engine
is running and then not so great.

I still have two of those Harris power supplies one runs an HT
monitoring a repeater and the other runs a scanner and a small
transmitter. The batteries are ten years old and show little
loss of capacity.



raypsi wrote in news:355e6bae-ab52-4d0e-8fde-
:

TI makes a really sweet ic for charging batteries the UC3906. Is the
greatest IC since sliced bread for charging batteries. It took forever
to charge my deep cycle marine battery like a110AHr. A straight
charger it would take a week to charge 100% it's that last 15% that's
the toughest. The UC3906 charged my deep cycle marine battery to full
charge from dead in 10 hours. It's one of the greatest homebrew jobs
I've done. I used it to charge a 110AHr deep cycle marine battery for
my electric bike. I could ride 2 days on a single charge like $0.25
worth of electricty back and forth to work. 45 miles on a single
charge.

73 OM
n8zu

On Nov 17, 7:41*pm, Grumpy The Mule wrote:
Agreed! *I designed a DC UPS power supply for Harris using the
UC3906 to charge a 4Ahr gell cell for wireless pbx. *The only
down side is it requires some head voltage for the regulator,
so it won't work well off a 12V vehicle system unless the engine
is running and then not so great.

I still have two of those Harris power supplies one runs an HT
monitoring a repeater and the other runs a scanner and a small
transmitter. *The batteries are ten years old and show little
loss of capacity.

raypsi wrote in news:355e6bae-ab52-4d0e-8fde-
:



TI makes a really sweet ic for charging batteries the UC3906. Is the
greatest IC since sliced bread for charging batteries. It took forever
to charge my deep cycle marine battery like a110AHr. A straight
charger it would take a week to charge 100% it's that last 15% that's
the toughest. The UC3906 charged my deep cycle marine battery to full
charge from dead in 10 hours. It's one of the greatest homebrew jobs
I've done. I used it to charge a 110AHr deep cycle marine battery for
my electric bike. I could ride 2 days on a single charge like $0.25
worth of electricty back and forth to work. 45 miles on a single
charge.

73 OM
n8zu- Hide quoted text -

- Show quoted text -

I think I am going to try charging it through a 10 amp constant
current source. If it works the way I am thinking as the battery nears
full charge the pass transistor should saturate applying nearly full
generator voltage across the battery topping off the battery. Im
thinking(hoping) that when this occours the voltage drop across the
transistor may be just enough to yield nearly the ideal float voltage
for the batteries.
The batteries normally power my heater and lights for my popup camper
and a couple of radios that are mostly used for rx. With only an
initial charge from the battey charger before leaving home I can camp
about 4 days. With some additioal charging I am hoping to extend it
another 2 oor 3 days. Since our trips usually include a few hours a
day of driving I thought I would use this oppurtunity to top off the
batteries. I have leaned against the idea of just running the engine
for that purpose. The incandescent bulbs I am using in the camper are
the main draw on the batteries perhaps going to LEDs would help.

Howdy,


The saturation voltage will probably be less than a volt,
likely only a few tenths of a volt. When the vehicle is
running the output voltage could be too high. A transistor
that comfortably handles the ten amps is going to be something
like a 2N2955 or 2N3055 there are curves on the data sheets
that tell the story. As the current souce runs out of compliance
and the current drops, the output voltage rises because the
saturation voltage decreases.

There is an easy fix if you use a PNP pass transistor. Clamp
the base at 13.6V plus a base emitter drop, say 0.8V, the output
can't rise higher than the float voltage.

Better yet, use a TL431 to sense the battery voltage to end the
constant current charge by reducing the bias and enter float mode.
(The TL431 is a very handy device and cheap. Check the app notes
and I'm sure you'll find many other uses for it.) Then either NPN
or PNP will work, choose your poison.

I modified a junky old eight amp Kmart charger like this with a
PNP device for charging the six volt battery in my tractor.

You'll need some sort of short circuit protection. During a short
the ten amps times the supply voltage will be dissipated in the pass
device. Could be a fuse or breaker or active protection. I left
this out of my first attempt and the pass device didn't like being
shorted for even a moment. Luckily I tested this before putting it
all back together rather than finding out later on in a snow storm.
The existing thermal breaker was much too slow.

LEDs would be a huge improvement.


73,
Grumpy


JIMMIE wrote in news:1fa6ec49-6eab-4cb6-8eeb-
:

I think I am going to try charging it through a 10 amp constant
current source. If it works the way I am thinking as the battery nears
full charge the pass transistor should saturate applying nearly full
generator voltage across the battery topping off the battery. Im
thinking(hoping) that when this occours the voltage drop across the
transistor may be just enough to yield nearly the ideal float voltage
for the batteries.
The batteries normally power my heater and lights for my popup camper
and a couple of radios that are mostly used for rx. With only an
initial charge from the battey charger before leaving home I can camp
about 4 days. With some additioal charging I am hoping to extend it
another 2 oor 3 days. Since our trips usually include a few hours a
day of driving I thought I would use this oppurtunity to top off the
batteries. I have leaned against the idea of just running the engine
for that purpose. The incandescent bulbs I am using in the camper are
the main draw on the batteries perhaps going to LEDs would help.

On Nov 18, 2:46*am, Grumpy The Mule wrote:
Howdy,

The saturation voltage will probably be less than a volt,
likely only a few tenths of a volt. *When the vehicle is
running the output voltage could be too high. *A transistor
that comfortably handles the ten amps is going to be something
like a 2N2955 or 2N3055 there are curves on the data sheets
that tell the story. As the current souce runs out of compliance
and the current drops, the output voltage rises because the
saturation voltage decreases.

There is an easy fix if you use a PNP pass transistor. *Clamp
the base at 13.6V plus a base emitter drop, say 0.8V, the output
can't rise higher than the float voltage.

Better yet, use a TL431 to sense the battery voltage to end the
constant current charge by reducing the bias and enter float mode.
(The TL431 is a very handy device and cheap. *Check the app notes
and I'm sure you'll find many other uses for it.) *Then either NPN
or PNP will work, choose your poison.

I modified a junky old eight amp Kmart charger like this with a
PNP device for charging the six volt battery in my tractor.

You'll need some sort of short circuit protection. *During a short
the ten amps times the supply voltage will be dissipated in the pass
device. *Could be a fuse or breaker or active protection. *I left
this out of my first attempt and the pass device didn't like being
shorted for even a moment. *Luckily I tested this before putting it
all back together rather than finding out later on in a snow storm.
The existing thermal breaker was much too slow.

LEDs would be a huge improvement.

73,
Grumpy

JIMMIE wrote in news:1fa6ec49-6eab-4cb6-8eeb-
:



I think I am going to try charging it through a 10 amp constant
current source. If it works the way I am thinking as the battery nears
full charge the pass transistor should saturate applying nearly full
generator voltage across the battery topping off the battery. Im
thinking(hoping) that when this occours the voltage drop across the
transistor may be just enough to yield nearly the ideal float voltage
for the batteries.
The batteries normally power my heater and lights for my popup camper
and a couple of radios that are mostly *used for rx. With only an
initial charge from the battey charger before leaving home I can camp
about 4 days. With some additioal charging I am hoping to extend it
another 2 oor 3 days. Since our trips usually include a few hours a
day of driving I thought I would use this oppurtunity to top off the
batteries. I have leaned against the idea of just running the engine
for that purpose. The incandescent bulbs I am using in the camper are
the main draw on the batteries perhaps going to LEDs would help.- Hide quoted text -

- Show quoted text -

Saturation voltage my oh my. A simple DC to DC convertor on the gate
of a FET of like 4 milli ohm so no more Vsat. I've done it with the
UC3906 which is designed to charge lead acid. All you need is a source
that'll will handle all that current. All the tricks I've seen done
with lead acid charging constant current will fawk up ur battery
unless you know when to shut it off like the UC3906 does.
Maybe 3 TL431's as sensors and you can do it. But the UC3906 can
sense a shorted cell and will not charge the battery if there is a
shorted cell.

73 OM
n8zu

Howdy,

Geez... I read this and it confused me. I haven't been
sleeping much and shouldn't post late at night.

The easy fix is to use an emitter follower circuit
where the the constant current load is connected to
the emitter. If you put the regulator in the Positive
side lead use an NPN.

In my instance the current regulator's pass transistor
is in the negative lead so the heatsink is at the same
potential as the vehicle chassis. No insulating hardware
is required.


73,
Grumpy

Grumpy The Mule wrote in
:


There is an easy fix if you use a PNP pass transistor. Clamp
the base at 13.6V plus a base emitter drop, say 0.8V, the output
can't rise higher than the float voltage.