Hey,
I'm currently working on a DIY stereo that will be powered by a 14.4V NiMH battery pack. I've already built a previous stereo with a similar design and the same style of battery pack, which I recharge with a "smart charger" I purchased online. My problem is this: If I turn on the stereo when the battery is charging, the charger produces noise on the line. I suppose this should be expected, as there is nothing regulating the power to the amplifiers (in this case, dual TDA7240A ICs), so the charging voltage is not only going to the battery, it's going right into the power supply for the ICs, decidedly not the best design. So I'd like to fix it in the next stereo. Is the solution as simple as adding a voltage regulator? If this is a solution, I'm thinking I'd want to use a regulator rated for the voltage of my battery pack (14.4V+). Is this a sound approach?
Thanks, SCW
I'm currently working on a DIY stereo that will be powered by a 14.4V NiMH battery pack. I've already built a previous stereo with a similar design and the same style of battery pack, which I recharge with a "smart charger" I purchased online. My problem is this: If I turn on the stereo when the battery is charging, the charger produces noise on the line. I suppose this should be expected, as there is nothing regulating the power to the amplifiers (in this case, dual TDA7240A ICs), so the charging voltage is not only going to the battery, it's going right into the power supply for the ICs, decidedly not the best design. So I'd like to fix it in the next stereo. Is the solution as simple as adding a voltage regulator? If this is a solution, I'm thinking I'd want to use a regulator rated for the voltage of my battery pack (14.4V+). Is this a sound approach?
Thanks, SCW
If you want to regulate your DC supply from batteries to remove the charger rip[ple, you'll need to have sufficient voltage difference between the battery supply voltage and the rail voltage(s) for series regulators not to 'drop out'.
For 78xx series regulators this is about 2.5volts minimum, however this can be less for a shunt regulator but this will reduce battery life....
hope this assists
Mik
For 78xx series regulators this is about 2.5volts minimum, however this can be less for a shunt regulator but this will reduce battery life....
hope this assists
Mik
It looks to me like you have basicly 2 options. You can regulate the power going to the batteries or the power going to the amp. I don't think I would regulate the charging voltage. NiMH batteries have special charging needs and if you have a charger that does the job of charging correctly don't mess with it. That leaves regulating the power to the amp. I would set up the amp to work on 12 VDC and regulate the output of the battery/charger. I think you should look for a LDO (low drop out) series regulator that need less than the 2.5 v that a 78XX needs. Or you could lower your operating voltage to 10.5 or so and use a LM317. That way as the battery ran down the amp would not be affected until you dropped out of regulation and any noise that the charging circuit makes is filtered out by the regulator.
Good luck BZ
Good luck BZ
Awesome, Thanks, this is what I wanted to hear.
I read you, BZed, I definitely don't want to mess with the charging voltage. That's why I bought a "smart" charger in the first place, NiMH batteries seem pretty finicky in their charge method, and I simply don't want to put the time into building the charger on my own... yet. (My charger was super pricey, $30+)
I'm going to give the LM317 approach a a shot, it seems like the way to go (I wasn't even aware that simple adjustable IC circuits like that were available, shows what I know.) I'm also thinking of trying out this new stereo with a 12V SLA (because it is one million times cheaper than the 12 AA NiMH battery pack I'm using). The LM317 will be easily adjusted for either battery... tremendous!
Thanks, SCW
I read you, BZed, I definitely don't want to mess with the charging voltage. That's why I bought a "smart" charger in the first place, NiMH batteries seem pretty finicky in their charge method, and I simply don't want to put the time into building the charger on my own... yet. (My charger was super pricey, $30+)
I'm going to give the LM317 approach a a shot, it seems like the way to go (I wasn't even aware that simple adjustable IC circuits like that were available, shows what I know.) I'm also thinking of trying out this new stereo with a 12V SLA (because it is one million times cheaper than the 12 AA NiMH battery pack I'm using). The LM317 will be easily adjusted for either battery... tremendous!
Thanks, SCW
Sorry, I must be misunderstanding something. Surely, when you "rock out on the go" you unplug the charger?
I used separate power supplies for he battery charger and amp. I have a dedicated smart charger for the battery, and it only goes to the battery. A switching power supply only goes to the amp. A switch toggles between battery and line power. Doesn't add a lot of weight or take up a lot of room--but it could be external if there are concerns along those lines.
Regulating the battery sucks some power and doesn't make sense to me.
I can post a pic of the way the switch and power supplies are wired if you like.
--Buckapound
Regulating the battery sucks some power and doesn't make sense to me.
I can post a pic of the way the switch and power supplies are wired if you like.
--Buckapound
For best life you never want to run a NiCad or NiMH 'dead' and never reverse polarize either chemistry. When cells are in series, one of them will always give up first at which point it reverse polarizes from the other cells delivering power through it.
G²
I think I get it. you want it kind of like the way a laptop computer charges/users power?
Another thing to consider is that the charger will probably not have enough current to both charge the battery and power the amp. Limiting current is a common feature of battery chargers, from what I know. Also, it seems possible that the current draw of the amp may change the way the charger operates, since it thinks it's only seeing a battery attached, and so may not operate as it is supposed to with respect to charging.
--Buckapound
--Buckapound
Excellent, thanks for all the input
Quick question Stratus46... I knew there were some risks in using and charging all the batteries as one big pack, and I haven't taken any major precautions yet try to extend the life of the pack (I think I probably should though, those puppies are expensive). Up until now, I usually charge the stereo before it goes completely dead. But now that you mention it perhaps I should add a failsafe into the newer model. What would you suggest? Perhaps an adjustable regulator that would just shut the stereo off if the supply voltage goes below some threshold value...? Any idea on the best way to do this. (Sorry, I'm going a bit off my own topic)
Thanks, SCW
Quick question Stratus46... I knew there were some risks in using and charging all the batteries as one big pack, and I haven't taken any major precautions yet try to extend the life of the pack (I think I probably should though, those puppies are expensive). Up until now, I usually charge the stereo before it goes completely dead. But now that you mention it perhaps I should add a failsafe into the newer model. What would you suggest? Perhaps an adjustable regulator that would just shut the stereo off if the supply voltage goes below some threshold value...? Any idea on the best way to do this. (Sorry, I'm going a bit off my own topic)
Thanks, SCW
NiCad / NiMH typically start at max voltage and fairly quickly drop to a plateau where they only slowly droop until they begin to rapidly decline. That's the point where you want to shut down and recharge. The voltage levels may be temperature sensitive.
If you are a little nuts, a microcontroller battery monitor might be a fun project. A built-in A-D converter and some software could make a fine battery monitor and consume very little power.
The Freescale (Motorola) bugs run 1-2 mA while operating so would not waste appreciable power. PIC processors can do this too. You have many options and would not be expensive and get an education to boot (pun intended). The radio controlled model folks have a great deal of info on batteries along with manufacturers of batteries and semiconductors.
Mission creep isn't too big a deal when you're simply using EEPROM already in the chip. Clocks, timers, LCD readouts are possible.
G²
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