# Charging 6V packs

• posted

A buddy just gave me a couple of 6V NiMH receiver flight packs.

Is there an inexpensive wall type charger available for these packs or do I need something like an Accu-Cycle for them?

DB

• posted

the same one you charge a normal receiver pack will charge it, just change the charging time to suit the packs capacity so if its a 50ma charger and a 800mah pack 800/50=16hours for a totally flat battery (and a bit extra for luck)

• posted

These are 5 cell, 6V packs. A regular wall charger is for 4.8V. They won't charge on a 4.8V wall charger, tried it.

DB

• posted

Most wall wart chargers are dumb chargers. They do not know how many cells the battery has. The wall charger should charge that pack. If it won't, there is either something wrong with the charger or the battery pack. If you have a voltmeter, hook it up to the battery pack and check it. I'm thinking a break in the wire in your battery pack. If the charger charges your 4 cell packs, then it should be ok for your 5 cell pack.

I would recommend getting one of those charger/cyclers. You can manage your batteries a whole lot easier with one. I have had the Triton and it worked fine. I now have the Multiplex LN-5014 and find it easier to set up.

• posted

Yes, the 4.8 volt chargers will not really do the job properly. However, you can make your own easily, if you have a 9 or 12 volt wall wart. It must be able to supply the current you require. Most will supply up to 300 milliamperes (.3 amps) and are suitable. You will want to charge the 6 volt pack, usually, at 1/10 the rated capacity. So, all you will need is a resistor in either the plus or minus line of the charger you are preparing. Let us say it is a 9 volt one...so you will want to drop the voltage by 3 volts (obviously if it is a12 volt charger, you will want to drop it by 6 volts). Now we use ohms law to find the value of the resistor which is E/I=R. That is the voltage (E) divided by the current (I) gives us the resistance (R). So let us say you have a 9 volt charger and the pack is say 800 mah rated. You are going to want to have 6 volts in at 80 mah (or in the formula .080 amps)..therefore 3 (volt drop) divided by the current 80 mah (.080) gives us 37.5 ohms. This is the value of the resistor you will use (or as close to it as you can get at Radio Shack). Now you need to know the wattage of the resistor. Again a formula I2R or properly written= current squared times the resistance gives us the power...so here we go again..we have the current of .080 squared is .0064 times the resistance, which in this case is 37,5 ohms...so the answer, .0064 times 37.5 is .24 or .24 watts to be specific...so you can use a 1 watt resistor and be perfectly safe. Any more questions, so I don't bore the heck out of everyone, please email me directly. Frank Schwartz

• posted

a purely resistance based option such as this "will not" and "can not" produce a known current charger, as the battery voltage is not constant you can just as easily over or undercharge your battery which goes to show a little knowledge of ohms law can be dangerous how ever well meaning the answer and as a side note sorry but my first answer was wrong my brand new Futaba RX and TX charger will not charge a 6 volt pack as the no load volts is only 5.8 volts but the charger I have used in the past for my 6 volt packs is an old Sanwa 4.8v rx charger it has a no load voltage of

7v and will charge a 6v pack, so I was wrong and I can still learn new tricks(and to make sure I have just tried them) Kevin
• posted

I'm thinking Franks advice is best so far. IMHO the Rx side of the wall wart won't charge it, but the TX side would. You'd have to monitor the pack so not to over charge it. mk

• posted

Characterization* of the Futaba charger FBC-8B(4) would tell you that a 5 cell Ni-Cd using the receiver side of the charger, would charge at 45 mA. Using the transmitter side it would charge at 80 mA. These chargers are essentially a constant power device, rather than constant current or voltage.

*plotting the voltage vs current output of the charger.

The minimum charge current to reliably charge Ni-Cds or Ni-Mh is C/20. You can charge a pack a lower rates but things begin to deteriorate rather quickly and you might end up with less than a full charge in a reasonable time period.

• posted

I have an article that addresses the use of various wall warts from cordless appliances and how to characterize them to use for charging your model batteries.

e-mail me if you want a copy of the .pdf file.

• posted

the new Futaba models like a MB82C03 wont charge a 6 volt pack as the no load volts is less than 6V

• posted

Actually, I do have an Accu-Cycle and it does charge the battery. So the battery is fine. As noted here, the Futaba wall charger just doesn't have enough poop to charge the 6V packs.

But the Accu-Cycle will only charge one receiver pack at a time. I'm looking to charge multiples. And with the help that folks have offered here I think I'm on my way.

Thanks guys, Dave

• posted

| a purely resistance based option such as this "will not" and "can not" | produce a known current charger, as the battery voltage is not constant | you can just as easily over or undercharge your battery which goes to | show a little knowledge of ohms law can be dangerous how ever well | meaning the answer

Yes, it will not produce a completely constant current, but it's usually close enough. C/10 vs. C/8 isn't a very big difference, after all, and when charging a NiCd or NiMH cell at a low rate, it'll usually get close to 1.4 volts rather quickly, even though it's not anywhere near fully charged.

| and as a side note sorry but my first answer was wrong my brand new | Futaba RX and TX charger will not charge a 6 volt pack as the no load | volts is only 5.8 volts

You've got to be careful how you measure this `no load voltage'. Your DC multimeter wants to measure a constant voltage, but the wal-warts used for chargers often have only a single rectifier and maybe some resistance to adjust the charge rate. The voltage may actually vary from 0 to 8 volts each cycle, but your multimeter will probably pick some voltage in between -- perhaps an RMS value if it's a good multimeter, and if not, who knows what it will pick?

| but the charger I have used in the past for my 6 | volt packs is an old Sanwa 4.8v rx charger it has a no load voltage of | 7v and will charge a 6v pack

... but it'll probably charge it more slowly than it'll charge a 4 cell pack.

Also note that you'll need *more* than 1.4 volts/cell to fully charge a NiCd or NiMH cells, so 7.0 constant volts probably is *not* enough to fully charge your 5 cell pack. But the voltage probably goes higher than that, so it may work anyways.

• posted

trouble is trying to work out when your battery is charged when you have no idea of the charge you have put in a bit like trying to fill a bath to a known level blindfolded with a hose from your garden

er no a resitance charger is of no use in charging NiCads, NiMh, lead acids, LiPo's, even a cheap charger will use a active current regulator a passive option will not be used at all The voltage may actually vary

• posted

| > Yes, it will not produce a completely constant current, but it's | > usually close enough. C/10 vs. C/8 isn't a very big difference, after | > all, and when charging a NiCd or NiMH cell at a low rate, it'll | > usually get close to 1.4 volts rather quickly, even though it's not | > anywhere near fully charged. | > | trouble is trying to work out when your battery is charged when you have | no idea of the charge you have put in a bit like trying to fill a bath | to a known level blindfolded with a hose from your garden

Cute analogy ... but fundamentally wrong.

When you overfill your bathtub, what happens? Water goes everywhere, then you get mold ...

When you overcharge your NiCd/NiMH battery at a low rate (around C/10), what happens? It gets warm. As long as you don't overcharge it like this for days at a time, no damage is done.

Wall-warts overcharge your NiCd/NiMH batteries. In small doses, this isn't a problem.

| > | Futaba RX and TX charger will not charge a 6 volt pack as the no load | > | volts is only 5.8 volts | > | > You've got to be careful how you measure this `no load voltage'. Your | > DC multimeter wants to measure a constant voltage, but the wal-warts | > used for chargers often have only a single rectifier and maybe some | > resistance to adjust the charge rate. | | er no a resitance charger is of no use in charging NiCads, NiMh, lead | acids, LiPo's, even a cheap charger will use a active current regulator | a passive option will not be used at all

Have you ever opened up a wal-wart charger for NiCd/NiMH batteries? If you do, you'll typically find a transformer, a single diode and maybe a resistor.

Perhaps there might be a bridge rectifier instead of a single diode (but I don't recall ever seeing this) but you're not likely to find a voltage regulator.

You'll probably find a voltage regulator in a charger meant for LiPo or Pb batteries, but they're charged differently and they're not what we're discussing here.

| > The voltage may actually vary from 0 to 8 volts each cycle, but | > your multimeter will probably pick some voltage in between -- | > perhaps an RMS value if it's a good multimeter, and if not, who | > knows what it will pick?

• posted

but if you dont know what you are putting in you have no idea if its charged over filling like a bath is ok but 1/2 filling the bath causes problems thats my point timed charging of batteries needs at least an idea of the current its no good putting a battery on charge for 14 hours and it takes 26 to charge it????

that I will agree on

• posted

| > When you overcharge your NiCd/NiMH battery at a low rate (around | > C/10), what happens? It gets warm. As long as you don't overcharge | > it like this for days at a time, no damage is done. | > | but if you dont know what you are putting in you have no idea if its | charged over filling like a bath is ok but 1/2 filling the bath causes | problems thats my point timed charging of batteries needs at least an | idea of the current its no good putting a battery on charge for 14 hours | and it takes 26 to charge it????

But Frank Schwartz's post (which you responded to) gave the math needed to calculate the appropriate resistor value for a desired charge rate.

... though he did make an error. I'd suggest assuming 1.4 volts/cell for purposes of calculating the charge rate rather than the usually given 1.2 volts/cell. While charging NiCd/NiMH cells, they go to 1.4 volts relatively soon. Using 1.2 volts instead for your math will give you a slower than desired charge rate.

In any event, you don't need any special equipment to determine when your slow charging (C/10 or so) wal-wart has fully charged your NiCd/NiMH batteries -- they will get warm when fully charged. If they're not warm, then either 1) they're not fully charged yet, or 2) they only became fully charged a few minutes ago, and haven't had time to get warm yet. Either way, let them charge some more.

I believe that the NiCd charge cycle is actually endothermic -- that the cells will get *cooler* as they charge during most of the cycle, as long as the charge rate is low. (I don't think NiMH cells do this, however.) Once the battery is fully charged, however, all that energy goes into heat, and the cells start getting warmer in both cases.

Though really, if you're at all serious about the hobby, I'd suggest getting a peak charger of some sort, even a cheap one, something that can charge either 1-8 cells (for glow fliers. `1 cell' capability is for the glow ignitor) or 4-8 cells (for glider fliers.) (If you're an electric flier, you'll also need something that can charge your power packs, which might be another charger entirely.)

If you ever forget to charge your batteries over night, it's just too tempting to try and push it with a few hours of charge. You really should have a peak charger of some sort, and then you can just use the wal-warts for the occasionally needed formative charges.

• posted

Try this from MPI - RX side charges 6V at 150mah, 4.8v at 180mah. I us

6V NiMH, form 1800 to 2700. I do a full charge for 18+ hours on th larger, and about 16hours for the smaller. I use TME pulse units tha then go to pulse leaving the batteries at a full charge. Never had an problems, and the cost is reasonable. My only complaint on the MPI wal charges, is the RX lead is very short. Either solder new leads or use servo extension - the drop is minimal.