First of all, I really wonder if you are protecting something that doesn't require protection.
You want to protect a Lithium battery back with charging circuit that says it was made for 13.5 volt operation. Their specification may be a bit vague, but the design may be okay.
Regarding the lighter socket...
The plug in it can wobble if something heavy is attached. That may cause disconnects. We live in a world where everyone makes adapters that exploit an existing socket in ways never intended.
Regarding searching the internet for a design...
Sometimes this works, but many times you are not so lucky. If you want a good solution for power takeoffs inside an automobile, the HAM radio community is likely to have more experience and knowledge to share than most of us. You really need to evolve a good specification of what you need, and then have someone that has made a lot of mistakes and learned, help you out. Amtel and EEtimes are very chatty about circuit designs, but they really are just trying to advertise what the do.. which is something else.
You can do better with a design from scratch by a HAM radio operator that does mobile HAM radio as your mentor.
If you want to use either the Amtel or EETimes schematic, it can be a front end to capture the majority of the destructive power in any transients... AND THEN add a switching voltage regulator to assure a regulated 12 votl output. Viola...
The charging voltage can get as high as 14.4V. If that is to be dropped to 12V, while at the same time delivering 2A, you're talking about getting rid of nearly 5W of heat.
Actually it can be worse than that - if the batteries dying and the regulator faulty (used to be very common in the
old days) then it might go a lot higher, 17V even... Of course then lots of indicator bulbs tend to fail and you'll
be going to garage to sort it out. So basically with an old vehicle its worse and the DC-DC converter option looks
most sensible. In fact one for the whole vehicle isn't a bad idea - combining the starter battery and vehicle electrical
system was a mistake from day one. These days they should be using a smaller deep cycle battery plus ultra-caps for
the starter motor??
The first circuit limits output voltage to 24V+; the second, to 27V. Is that good enough for what you're trying to accomplish?
-Phil
Oh yes, forgot to mention that I intend to modify the first circuit to lower the max Vout to around 13V and leave it as is. Otherwise perfect for my app.
A quote from one of the designers of those elegant and simple circuits might help:
"Conclusions
The input clamping circuit described above provides a low cost method to clamp the output voltage to a safe level, preventing potentially destructive over-voltage conditions for low voltage circuits. The circuit can be easily tailored by setting the output clamp voltage and capacitance for any load, and then adjusting the control loop. At typical input conditions, the pass element's forward voltage drop is quite low, resulting in low power loss and efficiencies higher than what is achievable with the use of a linear regulator.
John Betten is an application engineer for Texas Instruments. "
If you really need reliable 12.0 volts under all conditions, you might consider (don't laugh) a step up converter plus a step down converter. Sounds a bit silly, but boost up to ~18 volts then back down to 12.0. ...[/url]
@erco I wasn't laughing and your suggestion wasn't silly at all That's exactly what I tried first i.e buck-boost DC-DC converter as seen here.
That's "their" idea but after some thoughts I decided that I did not need it. A simple protection circuit should work plenty in my particular app. Thanks anyways!
But it it cuts out when the input is above 13V, it'll be off all the time with the engine running.
-Phil
Phil, I mean to limit Vout (i.e. modifying the original circuit to Vin=15V max and adding after it 4 diodes to get 4x0.7=2V8 voltage drop) so my protected circuit might always see less then 13V. As the LiPo charging circuitry can operate from as low as 5V and my pc down to 6V I do not really care about the accuracy of "12VDC" so to speak...
So it should work as expected ... not?
If you are going to tailor the spike filtering down from 20 volts, 13 volts may be too low and arbitrary. There are times the voltage regulator is going to have the alternator provide a constant voltage above that for extended periods to recharge the battery.
You should go above the maximum output selected by the automotive voltage regulator, something above 14.2 volts. In that way the filtering circuit will not have to dissipate energy for extended periods of time... smaller componets, less heat, more reliability.
These same reasons are pretty much why they chose a cut off at 20 and 27 volts. The more more power of the spike that you filter out, the larger your filter. They pretty much just wanted to catch the destructive force of higher voltage spikes and let the downstream dissipate the rest of the energy.
Going too low with just burn up the device quickly.
If you are going to tailor the spike filtering down from 20 volts, 13 volts may be too low and arbitrary. There are times the voltage regulator is going to have the alternator provide a constant voltage above that for extended periods to recharge the battery.
You should go above the maximum output selected by the automotive voltage regulator, something above 14.2 volts.
Be sure to check the V/I curve of the series diodes you choose. For example, at 3A, the nominal 0.6V forward voltage of a 1N4001 becomes 1.0V. Four of these diodes in series under those circumstances would drop 4.0V, not 2.4V.
Be sure to check the V/I curve of the series diodes you choose. For example, at 3A, the nominal 0.6V forward voltage of a 1N4001 becomes 1.0V. Four of these diodes in series under those circumstances would drop 4.0V, not 2.4V.
Comments
Duane J
The winner is this simple circuit : http://atmelcorporation.wordpress.com/2013/10/30/automotive-circuit-design-headaches/
There's also worth mentioning (2nd place) circuit: http://www.eetimes.com/document.asp?doc_id=1272768
I consider it solved - thank you.
-Phil
The ones I linked to can be panel mounted...
And they're IP67
You want to protect a Lithium battery back with charging circuit that says it was made for 13.5 volt operation. Their specification may be a bit vague, but the design may be okay.
Regarding the lighter socket...
The plug in it can wobble if something heavy is attached. That may cause disconnects. We live in a world where everyone makes adapters that exploit an existing socket in ways never intended.
Regarding searching the internet for a design...
Sometimes this works, but many times you are not so lucky. If you want a good solution for power takeoffs inside an automobile, the HAM radio community is likely to have more experience and knowledge to share than most of us. You really need to evolve a good specification of what you need, and then have someone that has made a lot of mistakes and learned, help you out. Amtel and EEtimes are very chatty about circuit designs, but they really are just trying to advertise what the do.. which is something else.
You can do better with a design from scratch by a HAM radio operator that does mobile HAM radio as your mentor.
If you want to use either the Amtel or EETimes schematic, it can be a front end to capture the majority of the destructive power in any transients... AND THEN add a switching voltage regulator to assure a regulated 12 votl output. Viola...
I can't beat ip67( Granted its 12V )
but panels are easy
http://www.powerwerx.com/powerpole-accessories/
i wish they dumped the cig plug on all cars for APPs .
Actually it can be worse than that - if the batteries dying and the regulator faulty (used to be very common in the
old days) then it might go a lot higher, 17V even... Of course then lots of indicator bulbs tend to fail and you'll
be going to garage to sort it out. So basically with an old vehicle its worse and the DC-DC converter option looks
most sensible. In fact one for the whole vehicle isn't a bad idea - combining the starter battery and vehicle electrical
system was a mistake from day one. These days they should be using a smaller deep cycle battery plus ultra-caps for
the starter motor??
Never seen those panels. May consider it instead.
And yeah, the cig plug should have been dumped a long time ago... together with the body of the first moron who thought to use it as a power outlet...
Oh yes, forgot to mention that I intend to modify the first circuit to lower the max Vout to around 13V and leave it as is. Otherwise perfect for my app.
A quote from one of the designers of those elegant and simple circuits might help:
"Conclusions
The input clamping circuit described above provides a low cost method to clamp the output voltage to a safe level, preventing potentially destructive over-voltage conditions for low voltage circuits. The circuit can be easily tailored by setting the output clamp voltage and capacitance for any load, and then adjusting the control loop. At typical input conditions, the pass element's forward voltage drop is quite low, resulting in low power loss and efficiencies higher than what is achievable with the use of a linear regulator.
John Betten is an application engineer for Texas Instruments. "
@erco I wasn't laughing and your suggestion wasn't silly at all
That's "their" idea but after some thoughts I decided that I did not need it. A simple protection circuit should work plenty in my particular app. Thanks anyways!
-Phil
Phil, I mean to limit Vout (i.e. modifying the original circuit to Vin=15V max and adding after it 4 diodes to get 4x0.7=2V8 voltage drop) so my protected circuit might always see less then 13V. As the LiPo charging circuitry can operate from as low as 5V and my pc down to 6V I do not really care about the accuracy of "12VDC" so to speak...
So it should work as expected ... not?
http://www.powerstream.com/DC-UPS-1212.htm
An interesting concept (added to my folder for future ref.) but a bit over for what I need at the moment - thanks anyway!
You should go above the maximum output selected by the automotive voltage regulator, something above 14.2 volts. In that way the filtering circuit will not have to dissipate energy for extended periods of time... smaller componets, less heat, more reliability.
These same reasons are pretty much why they chose a cut off at 20 and 27 volts. The more more power of the spike that you filter out, the larger your filter. They pretty much just wanted to catch the destructive force of higher voltage spikes and let the downstream dissipate the rest of the energy.
Going too low with just burn up the device quickly.
Thanks Loopy, I'm going 15V path.
-Phil
Good point Phil, thanks!