Topic: Electrical battery charging question

[MötleyRöx]

Only slightly related to motorcycles, but I trust this forum the most.
I have a 6volt/12volt charger that charges at 2,4 or 6 amps.  
It was originally meant for motorcycles batteries, and the like.
I now have a different charger for the bikes so it is collecting dust.
Could I change the connection on that to fit my 7.2volt RC car battery and use the 6volt setting at 2 or 4 amps?
My hobby battery charger took a crap and I'd rather not spend the money if it will work.  
The hobby charger charges from 0-6amps and 4-5amps is recommended for the batteries I use, which are 3000mah.
Does the question come down to nicd/nimh type vs. the auto/motorcycle type?
Thanks.

[MötleyRöx]

http://store.schumachermart.com/sc-600a.html

[kslrr]

Will not work.  In order for the 7.2v batteries to be charged at 4-5 amps, the charger needs to be able to go greater than 7.2v.  Your 7.2v batteries would only be charged to 6v.  Running it at 12v could damage your RC batteris.

[MötleyRöx]

Ok, so the hobby charger adjusts automatically for that difference?
RC cars regularly switch packs from 6 to 7 cells, or 6 volts or 7.2volts.
I am pretty sure that the electronic speed controls will run on either too.  
But, I do not know and would not consider the 7 cell over the 6, for obvious reasons.
So, no exploding, just not a great charge?
Someone with more RC knowledge than me may be able to answer that.

[kslrr]

Also, I believe that when a re-chargable battery is not charged to it's designed voltage, the life span will be decreased.

[TwoTired]

You should have stated whether the batteries are nicad or nimh.

The charger should "work", ie charge the batteries, but the automatic voltage trip points are set for a lead acid wet cell.

The high voltage fast rate charge should cease (peak at) at 7.1 volts, and switch to maintain the batteries at 6.1V or 6.6V (using the 6V setting).

The wet cell voltage is a nominal 2.1V/cell fully charged (rested).  During charge they can reach 2.4V/cell.
A nicad cell is 1.3V  charged (rested) During charge they can reach 1.4V.  So, an automatic charger intended for a wet cell battery won't be automatic for a Nicad.

Good nicad chargers monitor the battery charge voltage for delta peak.  When fully charged, the battery voltage drops about 10mV/cell, and the cells start to heat up.  Good nicad chargers notice this and reduce the charge current.

What is unknown is if your charger is a constant current type or constant voltage type.  However, it would seem that either would overcharge your nicad or nimh pack.

Your pack discharge rate is 3000mah or 3 amps (this is your C rating).  If you discharge at that rate you will notice battery heating (not good for batteries, recharge after cooling).
You can charge the batteries at that rate, too.  This would be the C/1 rate or 3 amps.  To avoid heating the pack, it is best to charge at C/10  (0.3 amps).  If you wish to maintain the battery at full charge the C/50 is desired and will keep the battery at full charge.  At a two amp rate you can expect the pack to heat up to unacceptable levels before reaching peak charge

If your charger is a constant current type, it will attempt to charge the battery at 2 amp.  You can monitor the battery for heat and charge voltage and disconnect when it is full.  But, don't expect it to be automatic for Nicad cells.

[TwoTired]

For more detail on charging batteries see;
http://www.wppltd.demon.co.uk/WPP/Batteries/Charging_Methods/charging_methods.html

[MötleyRöx]

Good info 2tired.  Thanks.

The reason I did not differentiate between nicd and nimh and simply stated the two kinds is because I have both.
Although, the nicd is basically a brick but still takes a charge that will not last more than 1 or 2 minutes.
The nimh takes a good charge and has lasted about 20-25 minutes with good power.

The charger is an oldie.  It has a dial to adjust the amperage from zero to 6 amps. 
So, it sounds like its the constant voltage type, from what you say.
It may have just blown a fuse, I still need to check, because while the better battery was not really getting hot, the charger was.

By everything you're saying, 2tired, it seems like it would be an ok thing to do for a not so loved battery pack and charger.  But, I would need to closely monitor battery temp.  Correct?

Of course I'd like to invest in a fancy charger, I was just hoping maybe I could get by.
I intend to go lipo at some point since I have the electronics capability already in the car.
But that is quite an expense in itself.

[TwoTired]

Have you been measuring the pack voltage, both when depleted and when charged?
Nicads are usually about .1 v/cell higher than nimh.  Just multiply by the number of cells to get pack voltage.  How old are these batteries?  They have caustic chemicals inside them that eventually corrode the bits inside that make power during discharge.  This effects their performance, naturally.
These batteries don't last forever and one cell can short, lowering the pack output.  Nicads can also develop "memory", where if they are not deeply cycled, lose their ability to provide current in duration.

If your charger has a dial to adjust current, it would seem more likely to be a constant current type, IMO.  Does the current diminish automatically, during charge.  If so, then it IS probably a constant voltage type, where the dial adjusts initial charge rate via voltage potential differentials between source and pack.   Does the charger have a brand/model number on it?

Have you charged the packs with higher than 3 amps?  How about when hot, like right after depleting?  Easy to damage cells with this sort of abuse.

[MötleyRöx]

Batteries are old enough that I almost don't care.  And, I have both types, nicad and nimh.  The good one (nimh) was free from an RC forum member but works pretty well.  Probably better than any that I had when I was a kid.

I do my best to follow the charger instructions, the battery marking recommendations, heat/feel test recommendations (which by the way the charger instructions point out as the best way).  But no, since I bought the vehicle I haven't checked measurements on it.  Call me lazy, but the garage where my meter is is very cold right now!

Breakin' out the allen wrench now, hoping its just a fuse.    If it is, I'm going to monitor the temp of the charger a lot more closely.

Still though, let me know everything you know.     Battery charger is still registering when I discharge the batt.

[MötleyRöx]

Here's the old RC10T (with battery) in question.
Also, the charger... maybe I should ask Chuck.

[MötleyRöx]

Does anyone see a fuse? 

[1080]

Looks like a circuit breaker on the bottom right hand corner. Press in with a pen it should reset and if pops again with no leads attached then you have a circuit problem.

[MötleyRöx]

It does not have any sort of popping or clicking feel.
Nothing happens w/ anything hooked up to the charger (input or output), or not hooked up, other than acting like it is discharging the battery.
I even tried to charge for a while and heat test the charger to see if the meter was faulty.  No heat.

Yes the battery is fine.  It is still discharged but powers up the car.  And the brick still powers up the car too.

[TwoTired]

This is the kind of troubleshooting a multimeter is made for.    But, if you are too lazy to go get it, I'm too disinterested to help further.

Call me lazy, but the garage where my meter is is very cold right now!

...unless you want to use your fingers to check if line voltage can be bridged across the black and white wires, of what is likely a circuit breaker in the upper right corner in the backside picture.  You want to feel a tingling sensation between the fingers with the unit plugged into the wall socket.
I wouldn't.  But, I also have no objections to using a multimeter to probe electrical circuits.

[Inigo Montoya]

Given the cheap prices for a charger, I would not bother to hook up a 6 volt charger. You might charge the batteries but it will damage them, not so that they do not work but power and life will be decreased quite a bit, especially the power as in voltage.
As for the difference in charging between nicd and nimh, when I was into rc, there was no difference other than the time it took to charge. nimh was a recent thing so people had questions and though they needed to be charged slower than nicd.
Given that a new battery can be had for about $15, they sound cheap but a new peak charger that is ac/dc is only $50.

Also, now this was a few years ago, it was demonstrated a couple times by the folks at R/C car action, that charging a battery below its rated voltage could increase the internal resistance of the cells.

Did you know that a dead shorted 7 cell pack could produce well over 100 amps? There is a lot of power in those little things.

[MötleyRöx]

This is the kind of troubleshooting a multimeter is made for.    But, if you are too lazy to go get it, I'm too disinterested to help further.

Call me lazy, but the garage where my meter is is very cold right now!

...unless you want to use your fingers to check if line voltage can be bridged across the black and white wires, of what is likely a circuit breaker in the upper right corner in the backside picture.  You want to feel a tingling sensation between the fingers with the unit plugged into the wall socket.
I wouldn't.  But, I also have no objections to using a multimeter to probe electrical circuits.

2tired.  Now, now.  The garage is buried in snow, I've been working since I started this thread, and there's no light in the garage for some reason.  I had a feeling you would be the one to call me lazy.   

But, I've got a day off.  I can make my way out there today.

I was thinking though.  wouldn't it be better to use my tongue than a finger?   

Yeah, Inigo, I'll probably end up getting a new charger if this one is toast.  Just sounds to be the better option, but Its still an interesting discussion.  And, like I said, the batts and motorcycle charger are not dear to me so, I wasn't too worried about killing either.

[MötleyRöx]

The meter showed no voltage, so I used my tongue.
No tingling.

Think its as simple as a non-operational circuit breaker?

[1080]

Looks like the circuit breaker is for the battery charge line. After looking at again the item I have circled is another item of interest. Could be another breaker or fuse compartment. It is hard to determine with photo angle. Is there any writing on that circled item?

[MötleyRöx]

Yes, there is.  It says Trimax pan-1.4a... sounds like fuse jargon to me.
Good eye.  I hadn't even noticed that was a separate piece from the breaker.
I also tested that breaker with a battery plugged in because I had that same theory as you... no voltage.

[1080]

 Sounds like a fuse, but your not out of the woods yet. Replacing it with a new fuse still could pop. 

 

[MötleyRöx]

Well, I think the charger got really hot.
I was putting a "good" charge into the battery and ran the charger for about 45 minutes.
Next time I went to charge, nothing.

So, perhaps, if it does work after a fuse change... I'll need to charge 15 minutes, cool, charge another 15, cool, etc.

[TwoTired]

That fuse is in the primary or "line" circuit, between line plug and transformer.  It kind of looks like a thermal self resetting breaker.  But, I can't find the numbers you referenced in their catalog, so I can't verify how it is supposed to work.
http://www.trimaxcb.com/site/home.php

Use your ohmmeter set to about 20000 ohms (or better yet auto range ohms) and measure across the wall plug (not plugged into the wall).  A fail condition on the meter would be infinity ohms, and indicates an open circuit.
You can then individually measure across the line cord breaker terminals, or the transformer primary itself.

If the breaker remains open circuit, despite resetting attempts, it will have to be replaced or defeated (safety alert).  If the transformer primary terminals read open circuit, you will need another transformer.

[MötleyRöx]

Ok.
Putting brain into think mode.
Will get back to you after testing and/or exploding.

[MötleyRöx]

Across the breaker are very low ohms.
The 'fuse' does look like a heat operated sort of doohickey.  All seems fine there too.
My meter doesn't show infinity... but, I am getting what I think would be that measurement across the transformer.  It reads as 1., which is what it reads when the leads are not connected in the ohm setting.