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Thread: Battery drain

  1. #21
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    Quote Originally Posted by OldSpark View Post
    Okay, how do you recover an auto-saved reply....? GRRRR!
    I've wondered the same thing but never gotten shafted. Bummer!

    You know mal, I thought the same thing but I was following a "tutorial" http://www.engblaze.com/hush-little-...p-mode-basics/

    I left my stuff all setup so I'll flash it a new sketch with output and report back tonight.

    OH and boy did my car start this morning. I thought it was going to roll over. That plus I had run the computer last night for about 5 minutes showing my uncle without the engine running or doing any charging. It would have been dead as a door nail on the last battery. So, problem solved, now to make things BETTER!

  2. #22
    North of the land of Hey Huns
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    Yeah the problem with that tutorial, is he uses a pullup resistor to trigger the AVR out of sleep mode (And he does it on pins 8-13... wtf?), which is a large drain on power. Your best bet is to use UART, or externally pull a pin down, and then flip it HIGH rather than LOW on the interrupt. This allows for zero I/O power usage, while still maintaining the interrupt.

    Glad to hear the new battery worked out for you, time to make the Arduino do all sorts of cool stuff for ya now that you don't have to worry if your car is going to start in the morning
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  3. #23
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    Yeah, I had already adapted that tutorial to be HIGH rather than LOW because immediately I saw that there would be constant power drain in standby. I guess I should have smelled the same stink with the rest of it

    The arduino is already doing tons of cool stuff. Perhaps it will do more in the future if the need arises. I need to do a work log but it does:

    ignition state
    computer power state
    power on/off computer
    ambient light sensor
    PWM for my screen backlight
    monitor steering wheel controls
    convertible roof switch (up or down)
    Dash lights
    Auxiliary power control for devices

    The Arduino and PC communicate back and forth talking about sensor status and settings from the PC (me) that need to be updated for backlight and stuff. Might do other stuff that I'm not thinking of right now. Originally it was to read the vss but I ended up just pulling speed from the GPS receiver instead.

  4. #24
    North of the land of Hey Huns
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    Wow, that's a lot of stuff. I definitely want to see a work log from you at some point, with some more details about your system

    Have you thought about tying it into OBD2? Scantool.net makes a really nifty breadboardable chip that is pretty much plug and play to let microcontrollers talk on the OBD2 bus.
    "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
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  5. #25
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    Yup, I'll get to the log. I'm just coming out of the full time bug ironing stage. The system is being reliable now so I'll have some spare time soon.

    I have an obdlink sx hooked to dash command. I'm not sure what I would use an arduino obd link for. I'm open to suggestions.

  6. #26
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    OldSpark,

    I've got a solar panel doing charging/maintenance on my secondary battery. Is it safe to keep the primary and secondary in parallel when the solar charger producing any juice?
    Former author of LinuxICE, nghost, nobdy.
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  7. #27
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    Yeah, should be fine.
    As long as batteries are charging (eg, typically above ~12.8V), they can't dump into each other.

    The whole "not paralleling" thing is to prevent a faulty battery dragging down the other and hence damaging that too.

    When paralleled for big loads or longer reserve times, that is ok (or rather, it's assumed to be necessary) provided both batteries are in similar condition - ie, no faulty battery or collapsed cells.
    The latter also applies to charging - a bad battery can drag the charger down and the good battery can discharge into the bad battery as well. Safety wise, that can be an issue - more current and hence heat to flame the bad battery. And a bigger charger might keep the voltage up, but the bad battery still absorbs the higher current.

    Also keep in mind excess voltage - that produces gassing which can be good for maintenance, but not for too long. Hence solar panels be regulated. Many say they don't need it for small panels, but I and many others disagree. Any overvoltage causes gassing. The only time a panel does not need a regulator is when its output is less than the battery's float current (ie - fully charged absorbed current; usually at a float voltage of ~13.2-13.4V) and they can vary from mA (maybe 100mA) to 1A or 2A for most car batteries.


    Pretty simple isn't it? (Not?)


    But here comes a bit more complexity...

    Since solar panels (should!) have blocking diodes (typically Schottky diodes for their lower voltage drop of ~0.3V instead of a silicon diode's ~0.6V drop), it should be simple enough to use parallel diodes - one to each battery from the panel.
    Hence batteries can remain isolated (for when not charging - ie, night time or reduced sun) yet still be charged by one solar panel panel.

    One problem may be the regulator which is usually between the panel's diode and the battery, however assuming the regulator has a remote battery voltage sensing wire (as opposed to sensing its output voltage), the diode(s) could be moved to the regulator output - ie, between the reg's output and each battery.

    If the reg does not have a separate/remote sensing wire, then the battery(s) will get ~0.3V less than they should (ie, a Schottky diode's forward voltage drop). That may not be too bad, though they should be properly charged at intervals if their charge voltage isn't above 13.8V or preferably more (13.8V is not enough to reverse the sulfation built up in a non-full battery).

    If the reg does has remote sensing, then a "sensed" battery must be chosen.
    I'd sense the battery that takes the lowest charge current (or has smaller loads) as that will have the smallest voltage drop across its diode. Higher currents increase diode voltage drops and it's better to undercharge one battery than overcharge the other (ie, gassing etc).
    However, if the regulator is set for say 14.2V, then the bigger or loaded battery could be sensed. That's based on a long-term maximum charge voltage of 14.4V for lead-acid batteries. Hence if the high current battery gets 14.2V through its diode, the low current battery might get 14.3V or which is still ok. EG - the sensed battery gets 14.2V with a 0.4V diode drop, hence the regulator is outputting 14.2 + 0.4 = 14.6V. The other battery might have a 0.3V diode drop due to less current thru its diode, hence it gets 14.6 - 0.3V - 14.3V, still 0.1V under the ROT 14.4V maximum.


    Some regulators have adjustable outputs which can be increased to compensate for diode voltage drops (especially if lacking remote sensing), or reduce their output voltage (from 14.4V) to ensure that with the lowest diode voltage drop, the battery's max charging voltage is not exceeded.

    If you think all that is tricky, you can imagine why diode isolators fell out of favor for automotive dual-battery setups. Their diode drops varied from ~0.6V to well above 1V at high currents; 1.4V was not unusual.
    What do you do when your 2 battery charging voltages differ by 0.5V etc? Which battery do you sense?
    [ I tackled many diode-isolator issues in two mp3car threads involving Simbalage (simbalage21?) who was adamant that they were "the only safe" and best form of isolator (and that relays were NOT isolators LOL!). Since then I have confirmed that no emergency services here use them. (Police vehicle's battery isolating relays are controlled by their (Delco?) EMS and regularly connect and isolate. Other emergency vehicles also use relays.) In fact quite a few baulked or laughed at the suggestion. Poor simbalage, taken in by the bullsh claims and half truths favoring wasteful & backward technologies and profits. ]


    I digressed...
    I've detailed the issues that can lead to a worst case situation. You are likely to find that they have little consequence, especially for small solar installations that do not provide huge currents and hence only have small diode voltage-drop variations (I think even less with modern Schottkys).

    For piece of mind, use your voltmeter. (A $10 DMM will do.)
    You should regularly check the OC (Open Circuit) voltage of the batteries. (Allow for surface-charge dissipation after charging.)
    Don't connect unequal (voltage) or "low voltage" batteries unless you know they are merely discharged.
    Ensure that the batteries get appropriate voltages and that the regulator else panels cannot over-charge.
    Now and again perform battery maintenance - ie, an equalisation charge etc. Else connect to the car's alternator for a good blast.
    And beware warm batteries, that's a sign of overcharging. However, siting in the sun or a hot car or engine bay or housing may have an effect (ha ha).


    Speaking of the sun, it has just risen.
    I'm off to bed.
    Last edited by OldSpark; 04-13-2012 at 04:14 PM.

  8. #28
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    Did another couple of tests. I set everything to output and low and that didn't make a difference. But then I got to thinking about the power LED. It stays lit while in sleep. For kicks I set pin 13 HIGH and let it sleep. Now they are 2 different LED's, one red one green and the red one is brighter so this is VERY approximate stuff... but it used 23.7ma not in sleep and 10.83ma!!!! in sleep. That's 3ma extra in sleep. Again, the green LED probably doesn't pull as much but then again, perhaps it does.

    Any harm in unsoldeing it? I don't need it as the thing is installed in my dash. I could always use pin13 as a faux power light via code.

  9. #29
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    The LED should be unnecessary. (Why do I say should?) Maybe you could cut or remove its resistor instead?
    Just don't heat other components too much or cause shorts (solder runs etc), and make sure the circuit is isolated (static discharge etc).



    FYI - my lost post included the Uno's onboard regulator being capable of 25V input (20V according to Arduino) BUT the recommend upper limit of 12V is for heating reasons - the reg will thermally limit itself (hence a brown-out situation - the worst power loss any uPC etc can suffer).
    Hence assuming some front-end 12V protection (spike suppression, cap filtering, and limiting to under 16V etc), it should be fine on a vehicle's 12V PROVIDED the Uno's voltage regulator gets additional heatsinking (or its current at up to 16V etc input is within its thermal tolerance).

    I can't remember the rest... and between this line and my last paragraph was a 1hour+ phone call, so I'm gonna have breakfast.

    But as to 10k pull-up resistors, that's 0.5mA (5V/10k) or ~1.2ma (12V/10k), but bigger resistors are possible - probably 100k (ie, 0.5 or .12mA) and maybe higher, but not 1M etc unless the input circuitry uses FETs (which is quite likely). (That's right, in my lost reply I opened with a complaint about people that cause me to go looking for data etc, as opposed to my ramblings from "memory" LOL!)

    And that auto-save recovery feature is usually available at the bottom left of "this" editing/reply panel. I have used it before after a PC freeze, though furryfox (firefox) is so good it usually puts me back to whatever was being replied to, and usually with only few edits/words lost. (I duplicated the tabs and tried mp3car's auto-saved stuff and chose the better of the two.) Unfortunately that last lost reply was because some idiot hit a history URL whilst on this page. That idiot usually right-clicks such links unless on a new tab, but what can I say, I am an idiot! And firefox has changed its caching method - I used to be able to find the latest cache file with the interrupted session text...
    Last edited by OldSpark; 04-14-2012 at 12:15 AM. Reason: minor edits

  10. #30
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    I'm not sure where the resistor is for the LED. I could try tracing. I did pull the LED from a broken arduino I had and it still seemed to function (as much as it did prior). I can't tell you how much less it pulled as it was broken and can't receiver or run a sketch. I also toasted my backup arduino as I tapped pin 2 to 12v rail when I looked away to the meter... DAMN!

    I did note that the recommended range limit was 12v. I guess I figured I would take my chances as I'm not pulling much power through the arduino so it shouldn't heat as much? If it browns out will it damage the PIC or just crash? I guess if it toasts I'll just buy a new one and put a regulator inline with the power I'm feeding it. Hind sight is always 20/20 as they say (funny cause I have 20/15 and was 20/10 when I was younger) but I have a 12v regulator on the circuit. Just would be VERY difficult to rewire to tap into that. Perhaps next winter I will rebuild my circuit or pay somebody I know to make me a printed board. Maybe I'll take a stab at printing myself. I hear laser printers and magazines work wonders

    Oh and I think the internal pullups are 20k.

    Pullup Resistors
    Often it is useful to steer an input pin to a known state if no input is present. This can be done by adding a pullup resistor (to +5V), or a pulldown resistor (resistor to ground) on the input, with 10K being a common value.
    There are also convenient 20K pullup resistors built into the Atmega chip that can be accessed from software. These built-in pullup resistors are accessed in the following manner.

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