I'm trying to replace the old style charger in an RV, with something that doesn't cost $20 per month to run or make a nonstop hum.
So, possibly a float charger that turns off when it isn't needed, and maybe power the charger from an inexpensive SMPS laptop power pack?
It would also be useful to relay switch off the main converter's ac input while the battery is within float range, since both converter and charger should be off while the battery has at least 12.6v~12.5v.
Help?
So, possibly a float charger that turns off when it isn't needed, and maybe power the charger from an inexpensive SMPS laptop power pack?
It would also be useful to relay switch off the main converter's ac input while the battery is within float range, since both converter and charger should be off while the battery has at least 12.6v~12.5v.
Help?
The OP description isn't really a float charger, which ideally is charge rate=self-discharge rate. Otherwise, I agree a window comparator is in order, but if the supply input is to be cut off then an auxiliary power source is required. That might be easier to do with a CMOS watchdog and alkaline cells rather than some sort of monitor-its-own-voltage-source circuit.
I was under the impression that 'Float Charging' was applying the charging voltage continuously which needs to be well regulated and ideally temperature compensated.
To maximise the battery life by preventing under charging it helps to have a boost charge facility as well.
There are some integrated circuits around to do this such as the Texas Instruments bq24450. I guess that there are others. It's possible to roll your own with comparators and someting like a 723 Voltage Regulator but why bother.
To maximise the battery life by preventing under charging it helps to have a boost charge facility as well.
There are some integrated circuits around to do this such as the Texas Instruments bq24450. I guess that there are others. It's possible to roll your own with comparators and someting like a 723 Voltage Regulator but why bother.
I guess this is not a Lead-acid battery? If it was then there would be no point in turning the charger off, just ensure that it has a properly temeperature-compensated float voltage. The temperature sensor needs to be a remotely connected one so that it can be attached to the battery (or batteries) under charge.
A Ni-Cad or Lithium rechargable battery pack will need to be disconnected when the batteries reach full charge, but each of these battery technologies require their own dedicated charger.
A Ni-Cad or Lithium rechargable battery pack will need to be disconnected when the batteries reach full charge, but each of these battery technologies require their own dedicated charger.
Something like this?
AC --> AC relay contacts -> 19.5V AC adaptor --> LM317/350 configured as a current regulator --> reverse voltage protection diode --> LM317/350 configured as a voltage regulator ---> 12V battery
12V battery --> comparator circuit w/reference and hysteresis --> FET --> AC relay coil
AC --> AC relay contacts -> 19.5V AC adaptor --> LM317/350 configured as a current regulator --> reverse voltage protection diode --> LM317/350 configured as a voltage regulator ---> 12V battery
12V battery --> comparator circuit w/reference and hysteresis --> FET --> AC relay coil
Reverse protection diode can go anywhere in the chain, having it after the voltage regulator puts a diode drop after the regulator which isn't too constant. But for charging a 12V battery, it's probably fine there.
The comparator circuit is pretty easy to pull off. Power the comparator off a 7805/08/09 or whatever's in the junk bin, and divide that voltage with a pair of resistors to establish your reference - connect this to the + terminal of the comparator. Divide the battery voltage with another divider and connect it to the - terminal. Run a hysteresis resistor from comparator output to the + terminal, sized proportionally to the reference divider resistor values to establish the proper hysteresis level.
Feed the comparator output into a logic level NFET (IRLZ24 or whatever, size doesn't really matter) and use this to switch the negative side of the AC relay coil, positive side connected to battery +.
Make sure you fuse the whole circuit. Shorting a lead acid battery can be dangerous.
The comparator circuit is pretty easy to pull off. Power the comparator off a 7805/08/09 or whatever's in the junk bin, and divide that voltage with a pair of resistors to establish your reference - connect this to the + terminal of the comparator. Divide the battery voltage with another divider and connect it to the - terminal. Run a hysteresis resistor from comparator output to the + terminal, sized proportionally to the reference divider resistor values to establish the proper hysteresis level.
Feed the comparator output into a logic level NFET (IRLZ24 or whatever, size doesn't really matter) and use this to switch the negative side of the AC relay coil, positive side connected to battery +.
Make sure you fuse the whole circuit. Shorting a lead acid battery can be dangerous.
Thanks guys!
I don't have an objection to relay logic if it might help avoid a circuitous collection of transistors, but in either case, perhaps a schematic or sketch could make whatever it is a bit more clear.
If left off the charger for 1 hour, or up to 2 days (or more!), the new style marine batteries will all be about 12.6v. I don't see any need for the charger to run nonstop and abuse the battery during those 2 days. I guess that is how the batteries get killed. So, I'd rather the charger turn off--that would at least be more efficient and cooler, wouldn't it?
I don't have an objection to relay logic if it might help avoid a circuitous collection of transistors, but in either case, perhaps a schematic or sketch could make whatever it is a bit more clear.
It is to charge the new style marine batteries. My old charger shoves at it nonstop trying to tip just over 13.5, but she won't go and both the battery and charger gets hot and then you go buy a new battery, again, again. Oh bother.
If left off the charger for 1 hour, or up to 2 days (or more!), the new style marine batteries will all be about 12.6v. I don't see any need for the charger to run nonstop and abuse the battery during those 2 days. I guess that is how the batteries get killed. So, I'd rather the charger turn off--that would at least be more efficient and cooler, wouldn't it?
Reverse protection strongly implies that what's protected is behind; is your vreg protected from reverse voltage? I doubt too that the junction thermal coefficient is critical to this design. Single op amp window comparators aren't without their own issues, so I don't understand not using a jellybean dual comparator to pull this off. Actually, I like this 3-comparator approach, where the third comparator provides a charge status indicator.
I have in the past few weeks (for work) designed a charger for a sealed lead-acid (valve regulated) 24V 65 amp-hour battery pack. If the float charge voltage is set correctly (around 27.6V at 20C in this case) then the current taken by even these 65Ah batteries (Yuasa NP-L range) drop to around 60mA with new batteries. Lead-acid batteries get killed by leaving an excessive voltage across them when they should be in a float-charge regime with the float voltage temperature compensated.
Is the battery supplying current to a load all the time, even with the charger connected? If this is the case, then having a system where the charger is turned off when the battery is fully charged, and turned back on again when the voltage has fallen to a specified value is a sensible solution of course. Perhaps a cheap 'Arduino' single-board computer might be a good way to control things?
Is the battery supplying current to a load all the time, even with the charger connected? If this is the case, then having a system where the charger is turned off when the battery is fully charged, and turned back on again when the voltage has fallen to a specified value is a sensible solution of course. Perhaps a cheap 'Arduino' single-board computer might be a good way to control things?
Thank you for finding that outdated article which is good for showing the problem, as it will surely break the new marine/rv batteries. Likewise, it is so difficult to buy an updated battery charger that doesn't kill the new marine batteries--Most of the outdated chargers are built with the same assumptions as that article, with the result of about $120 waste per replacement battery per each charger mistake.
Problem: Marine/Rv battery makers didn't pause to ask anyone's permission prior to changing battery specs, and the state of the art charger design (and that article) ruins the new batteries.
Stopgap fix: Car batteries are compatible with the too high voltage of the latest overchargers. And the car batteries last longer than breaking the marine batteries in just 2 weeks.
Again, I need to charge up to 13.5 (13.5~13.6 MAX!), then turn off completely and then await the battery to fall to 12.5v (12.5~12.7) before turning back on. That specification hasn't changed since the thread title.
I thought someone might have a nice quick simple idea like a strong ccs, a zener and a relay or something just brilliantly easy like that.
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That article only substantiated my recollection that the ideal lead-acid charger has a constant-current phase, followed by a constant-voltage phase, followed by a maintenance phase. There doesn't seem to me to be a truly easy way to achieve that.
You haven't said how big the battery is. Maybe you could get by with just the ccs, window comparator, and relay circuits.
You haven't said how big the battery is. Maybe you could get by with just the ccs, window comparator, and relay circuits.
Or, an end user adjustable charger would be really great!
But I wouldn't want yet another digital chip that is determined to either overcharge or power off unexpectedly (usually both), and while all of those have such lovely advertisements and promises on the package, what really happens is a lot of attempted interaction what with beeping and blinking as well as not maintaining any settings through a power outage and it eventually forgets to work. Thus of course, with the digital charger, the battery is first ruined then run down. Well, I didn't want that particular sort of adjustment.
But I wouldn't want yet another digital chip that is determined to either overcharge or power off unexpectedly (usually both), and while all of those have such lovely advertisements and promises on the package, what really happens is a lot of attempted interaction what with beeping and blinking as well as not maintaining any settings through a power outage and it eventually forgets to work. Thus of course, with the digital charger, the battery is first ruined then run down. Well, I didn't want that particular sort of adjustment.
you can give this circuit a try:
A New Solar / Wind Charge Controller Based on the 555 Chip
just change the thresholds to what you need (uses separate trimmers for the upper and lower threshold) but you'll also need to make a current limiting circuit since it is designed to be used with solar panels which act like current sources.
One needs to add a means to disconnect the 7805 (and associated active circuit) when the input falls below a useful battery charger threshold. If that were not done, the Solar rig is running the 7805 all NIGHT long discharging the battery, the wind rig still runs the 7805 when the wind does not blow and the AC powered rig leaves the 7805 running after you unplug. . . eventually dropping the battery below threshold causing irreversible battery damage. For wind and solar this is daft. For AC, I just need an ac powered relay to enforce thoroughly disconnecting the charger when the AC is disconnected.
Anyone got a more energy efficient detector, such as one that does not cause chargers to drain batteries?
Anyone got a more energy efficient detector, such as one that does not cause chargers to drain batteries?
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