Suppose you have a device (HF transceiver) that requires 11.7V to 15.8V
DC to run and you want to run it from lead acid batteries. If you use a
12V (6 cell) battery, a large part of the battery life will be to low of
a voltage to run the radio, especially when you take into account the
voltage drop in the power wire. A 7 cell battery would be great but
I've never seen one and I can't find single cells to make my own pack
that aren't gigantic.

So it seems to me the best solution is a DC to DC converter. What I am
wondering is would it be easier to step up the voltage of a 12V battery
when it drops below say 12V or step down from 24V? Depending on the
radio I use, I will need between 20 to 40A peek, average current should
be much less though.


--
Chris W
KE5GIX

"Protect your digital freedom and privacy, eliminate DRM,
learn more at http://www.defectivebydesign.org/what_is_drm"

Ham Radio Repeater Database.
http://hrrdb.com

" Chris Wanker "
>
> Suppose you have a device (HF transceiver) that requires 11.7V to 15.8V DC
> to run and you want to run it from lead acid batteries.


** That voltage range shows it has been DESIGNED to run from a lead-acid
battery - while under charge or not.


> If you use a 12V (6 cell) battery, a large part of the battery life will
> be to low of a voltage to run the radio,

** Absolute BOLLOCKS !!!!!!!!!!!!!!


> especially when you take into account the voltage drop in the power wire.

** Use thick enough wire - fool.


> So it seems to me the best solution is a DC to DC converter.


** Ridiculous.



> Chris W
> KE5GIX

** Says it all.



...... Phil

On Fri, 14 Mar 2008 17:43:38 +1100, Phil Allison wrote:

> " Chris Wanker "
>>
>> Suppose you have a device (HF transceiver) that requires 11.7V to 15.8V
>> DC to run and you want to run it from lead acid batteries.
>
>
> ** That voltage range shows it has been DESIGNED to run from a lead-acid
> battery - while under charge or not.
>
>
>> If you use a 12V (6 cell) battery, a large part of the battery life
>> will be to low of a voltage to run the radio,
>
> ** Absolute BOLLOCKS !!!!!!!!!!!!!!
>
(balance of tirade snipped)

Even for a slow (> 10 hour) discharge, a lead acid battery's terminal
voltage is about 1.75V/cell, or 10.5V for a 6-cell, '12V' battery.

Nominal cell voltages are just that -- nominal. Usually they're the
unloaded voltage of the cell after it's discharged for a bit. If you
want to extract all the useful energy in a battery, you have to take
things much lower than the nominal.

More like they were designed to run off of nominal automotive voltages,
with the expectation that you'd have the car running when you were in
transmit.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

On Fri, 14 Mar 2008 00:46:29 -0500, Chris W wrote:

> Suppose you have a device (HF transceiver) that requires 11.7V to 15.8V
> DC to run and you want to run it from lead acid batteries. If you use a
> 12V (6 cell) battery, a large part of the battery life will be to low of
> a voltage to run the radio, especially when you take into account the
> voltage drop in the power wire. A 7 cell battery would be great but
> I've never seen one and I can't find single cells to make my own pack
> that aren't gigantic.
>
> So it seems to me the best solution is a DC to DC converter. What I am
> wondering is would it be easier to step up the voltage of a 12V battery
> when it drops below say 12V or step down from 24V? Depending on the
> radio I use, I will need between 20 to 40A peek, average current should
> be much less though.

I'd step up from below, either with a flyback converter or with an
isolated output, connected between the battery's positive terminal and
your load. Then the converter only needs to supply the difference
between the battery output and 12V.

I haven't actually done it, so I dunno the right answer.

You may find that some of your gear works just fine down to the bitter
end of your discharge curve, 11.7V rating or no.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

"Tim Wescott"
" Chris Wanker "
>>>
>>> Suppose you have a device (HF transceiver) that requires 11.7V to 15.8V
>>> DC to run and you want to run it from lead acid batteries.
>>
>>
>> ** That voltage range shows it has been DESIGNED to run from a lead-acid
>> battery - while under charge or not.
>>
>>
>>> If you use a 12V (6 cell) battery, a large part of the battery life
>>> will be to low of a voltage to run the radio,
>>
>> ** Absolute BOLLOCKS !!!!!!!!!!!!!!
>>
> (balance of tirade snipped)
>
> Even for a slow (> 10 hour) discharge, a lead acid battery's terminal
> voltage is about 1.75V/cell, or 10.5V for a 6-cell, '12V' battery.


** Irrelevant garbage.

Standard lead-acid ( ie car ) batteries are NOT designed for deep
discharge.

It destroys them very quickly.

An end point of 11.7 volts is a safe one and gets the most LIFE from such
batteries.



> Nominal cell voltages are just that -- nominal. Usually they're the
> unloaded voltage of the cell after it's discharged for a bit. If you
> want to extract all the useful energy in a battery, you have to take
> things much lower than the nominal.


** Not with standard car batteries you DON'T !!!


> More like they were designed to run off of nominal automotive voltages,


** Yep.

Bet the Tx still operates fine at 10.7 volts too.

While destroying the damn battery.




....... Phil

On Sat, 15 Mar 2008 15:25:39 +1100, Phil Allison wrote:

> "Tim Wescott"
> " Chris Wanker "
>>>>
>>>> Suppose you have a device (HF transceiver) that requires 11.7V to
>>>> 15.8V DC to run and you want to run it from lead acid batteries.
>>>
>>>
>>> ** That voltage range shows it has been DESIGNED to run from a
>>> lead-acid battery - while under charge or not.
>>>
>>>
>>>> If you use a 12V (6 cell) battery, a large part of the battery life
>>>> will be to low of a voltage to run the radio,
>>>
>>> ** Absolute BOLLOCKS !!!!!!!!!!!!!!
>>>
>> (balance of tirade snipped)
>>
>> Even for a slow (> 10 hour) discharge, a lead acid battery's terminal
>> voltage is about 1.75V/cell, or 10.5V for a 6-cell, '12V' battery.
>
>
> ** Irrelevant garbage.
>
> Standard lead-acid ( ie car ) batteries are NOT designed for deep
> discharge.
>
> It destroys them very quickly.
>
> An end point of 11.7 volts is a safe one and gets the most LIFE from
> such batteries.
>
>
>
>> Nominal cell voltages are just that -- nominal. Usually they're the
>> unloaded voltage of the cell after it's discharged for a bit. If you
>> want to extract all the useful energy in a battery, you have to take
>> things much lower than the nominal.
>
>
> ** Not with standard car batteries you DON'T !!!
>
>
>> More like they were designed to run off of nominal automotive voltages,
>
>
> ** Yep.
>
> Bet the Tx still operates fine at 10.7 volts too.
>
> While destroying the damn battery.
>
Oh gee, Phil, it's so nice that you're willing to talk to all of us even
though you're so much smarter than everyone else. You must be a social
disaster if you can't find people as smart as you to hang with.

So, where _exactly_ does the OP mention that he's using car batteries in
the original post? All I see is "lead acid", with no mention that
they're not, indeed, deep discharge.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

"Tim Wescott"

>
> So, where _exactly_ does the OP mention that he's using car batteries in
> the original post? All I see is "lead acid", with no mention that
> they're not, indeed, deep discharge.


** So, anyone here is 100% ENTITLED to presume they are NOT !!

YOU POSTURING ASS.




........ Phil

Tim Wescott wrote:
> On Sat, 15 Mar 2008 15:25:39 +1100, Phil Allison wrote:
>
>> "Tim Wescott"
>> " Chris Wanker "
>>>>> Suppose you have a device (HF transceiver) that requires 11.7V to
>>>>> 15.8V DC to run and you want to run it from lead acid batteries.
>>>>
>>>> ** That voltage range shows it has been DESIGNED to run from a
>>>> lead-acid battery - while under charge or not.
>>>>
>>>>
>>>>> If you use a 12V (6 cell) battery, a large part of the battery life
>>>>> will be to low of a voltage to run the radio,
>>>> ** Absolute BOLLOCKS !!!!!!!!!!!!!!
>>>>
>>> (balance of tirade snipped)
>>>
>>> Even for a slow (> 10 hour) discharge, a lead acid battery's terminal
>>> voltage is about 1.75V/cell, or 10.5V for a 6-cell, '12V' battery.
>>
>> ** Irrelevant garbage.
>>
>> Standard lead-acid ( ie car ) batteries are NOT designed for deep
>> discharge.
>>
>> It destroys them very quickly.
>>
>> An end point of 11.7 volts is a safe one and gets the most LIFE from
>> such batteries.
>>
>>
>>
>>> Nominal cell voltages are just that -- nominal. Usually they're the
>>> unloaded voltage of the cell after it's discharged for a bit. If you
>>> want to extract all the useful energy in a battery, you have to take
>>> things much lower than the nominal.
>>
>> ** Not with standard car batteries you DON'T !!!
>>
>>
>>> More like they were designed to run off of nominal automotive voltages,
>>
>> ** Yep.
>>
>> Bet the Tx still operates fine at 10.7 volts too.
>>
>> While destroying the damn battery.
>>
> Oh gee, Phil, it's so nice that you're willing to talk to all of us even
> though you're so much smarter than everyone else. You must be a social
> disaster if you can't find people as smart as you to hang with.
>
> So, where _exactly_ does the OP mention that he's using car batteries in
> the original post? All I see is "lead acid", with no mention that
> they're not, indeed, deep discharge.
>

Deep Cycle or not,It's better not to cycle any lead acid battery below
50% depth of discharge,for best life..The more 'shallow' the
discharge,the longer they will last. You can drain them down to 10.8V a
few times,but not on a constant basis,they will only take that kind of
punishment a couple times before they fail completely.

11.7-15V sounds like the usual '12Volt/automotive use' voltage range.

On Mar 14, 6:46=A0pm, Chris W <1qaz...@cox.net> wrote:
> Suppose you have a device (HF transceiver) that requires 11.7V to 15.8V
> DC to run and you want to run it from lead acid batteries. =A0If you use a=

> 12V (6 cell) battery, a large part of the battery life will be to low of
> a voltage to run the radio,

If you have a good lead acid battery and you keep below C/10 amps, you
should be above 11.7 for at least 50% of total capacity. If you are
going to draw say C/5 amps then 11.7 will be reached in 30% of total
capacity. Here are some curves that will give you what you need to
know

http://www.arttec.net/Solar_Mower/4_Ele ... arging.pdf

Cheers

Chris W wrote:
> Suppose you have a device (HF transceiver) that requires 11.7V to 15.8V
> DC to run and you want to run it from lead acid batteries. If you use a
> 12V (6 cell) battery, a large part of the battery life will be to low of
> a voltage to run the radio, especially when you take into account the
> voltage drop in the power wire. A 7 cell battery would be great but
> I've never seen one and I can't find single cells to make my own pack
> that aren't gigantic.
>
> So it seems to me the best solution is a DC to DC converter. What I am
> wondering is would it be easier to step up the voltage of a 12V battery
> when it drops below say 12V or step down from 24V? Depending on the
> radio I use, I will need between 20 to 40A peek, average current should
> be much less though.
>
>

I think the "best solution" is to add a circuit that warns you
to shut down - or automatically disconnects the load - when the
voltage drops to ~ 11.7. The idea is to protect the battery
when that voltage is reached, not to get more out of it.
Discharging a lead acid battery too far damages it.

Ed