NiCad Battery Charger repair

No.

Probably not.

Repair the one you have.

snipped-for-privacy@mindspring.com wrote in news: snipped-for-privacy@h2g2000hsg.googlegroups.com:

It MIGHT help if you identified WHAT the "mid-1980's equipment" IS;make,model,serial number. Somebody here may have a manual or link to one.

innews: snipped-for-privacy@h2g2000hsg.googlegroups.com:

Hello Jim and thanks for the input. I was afraid that I had already given too much information!

The equipment is a Topcon GTS-2B Geodetic Total Station, used for land surveying. Most of the device is mechanical or optical/mechanical, but the distance measuring function uses an 8.4 volt battery pack.

The battery charger is a Topcon Battery Charger BC-10B, which is used for standard rate charging. When using the standard battery pack, the BT-5Q (DC 8.4V output and 1.2AH capacity) the recommended charge time is 8 hours.

Again, any ideas or suggestions will be appreciated.

What's the history? Did it work yesterday and not today? Did you pull it out of a dumpster? If the latter, idle NiCd batteries go shorted and burn up stuff when you turn on the charger.

A significant clue is that the fuse is blown, but you gloss over that fact and don't describe where in the circuit it is. It ain't likely to work with a blown fuse. The problem is likely downstream of the fuse.

If you've got 15V on one side of the resistor and nothing on the other you've got no current, which is consistent with a blown fuse. Also consistent with open resistor or dogbone.

It's likely that the led illuminates only when there's sufficient current to generate some volts across the dogbone.

Start with the blown fuse. Check for shorted batteries. mike

--------------------- the LED should lite loaded or not u mentioned no load output what is the load u r putting on it? is it a switching power supply 100-260Vac 50~60Hz or a linear PS if bottom regulation voltage can be seen to ring when u lower ac input on your scope then it is linear

Mike. Thanks for the questions. Let me expound on the situation so that you and others may have more to ruminate on as to my battery charger situation.

Battery charger (Topcon BC-10B) was properly charging the battery pack on a GTS-2B "Total Station" (used for surveying). I had miswired the connector to another port on the GTS-2B. Noticed a problem when saw that the Red LED "charging" light was out. Checked battery charger's output at the plug - saw more than 15 VDC. Then also noticed the blown fuse on the GTS-2B.

Since the voltage read at the connector (15.39 VDC) was well above the BC-10B's stated output of 10.43VDC and the battery pack is made up of seven ni-cad cells (8.4 VDC) I was concerned that the BC-10B battery charger was way out of tolerance.

As this is a simple, plug in the wall battery charger, I started looking for a replacement. Topcon wants $120 for theirs. At that point it was worth opening up to try to find the problem.

No dumpster diving on this one. The battery pack was properly functioning and the problem occured only after I miswired the hook-up connectors while starting to recharge the battery pack.

The fuse is on the GTS-2B equipment (actually associated with the battery pack and it even has an On/Off switch that controls both output (into the GTS-2B from the battery pack for distance measuring operations) and input (for charging the battery pack - the switch must be On for charging operations.)

I have +/- 15.4VDC (depending on the line current, it was 15.39 with the line current at 121.4 VAC and directly proportional increase as the line current changed) coming out of the battery charger, which I initially measured at the charger's plug. Now that I have taken the battery charger module apart, I measure a similar voltage at any point after the current is rectified (the diodes are immediately after the secondary side of the transformer.)

Have +/- 15.4vdc on both sides of the resistor when tapping to the secondary side's center output post (supplies the negative for the output plug).

The mention as to the 0.000 VDC was when I check the voltage of the two legs going into the Red LCD.

One leg of the LED terminates into the output side of the 68 ohm resistor.

On the output side of the "dog-bone" is a Tee where one leg runs to the output plug as the Positive terminal and the other leg from this Tee becomes the "other" leg into the Red LCD.

I do read +/- 68 ohms across the resistor as it sits, still wired into the charger, but the charger's output jack is not hooked up to the battery pack (and stating the obvious, not plugged into the line current!)

Believe the "dog-bone" is a capacitor, but was not 100% certain. Is what I described as a "dog-bone" a Ceramic Tubular Capacitor, and if so, what capacity with the White(Silver?) / Gold / Gold / Gold banding?

The "dog-bone" is still hooked up. Everything is still as it was as I have only opened the battery charger case without breaking any connections, up to this point.

The "dog-bone" has +/- 15.4VDC on both sides. Do not have an easy way to measure the current at this time. Possibly, I could hook up a small automotive lamp to the plug to see if there is current.

To review, the blown fuse and the batteries (which still have minimal charge) are on the GTS-2B equipment. Replaced the fuse and the GTS-2B equipment still works.

It is only because I no longer have an illuminated Red LED and my checking of the output voltage (and my belief that this is way to high) that I believe that I have a problem.

Do you think that I do have a problem (of course, I mean with the battery charger!) and if so, any ideas of how to correct it/them?

Again, thanks for your input and attempts to help me.

If you managed to introduce a charged battery the wrong way round to the charger that might account for a blown LED - they are polarity sensitive.

Voltage doesn't matter when charging Ni-Cads - within a wide range, provided it is higher than the nominal pack voltage. It's the current through the pack which is important and in this case (in the main) is set by the series resistor.

It has so few components it should be simple to test them all with a DVM - and to see if it is actually producing charging current. The LED can be checked by simple substitution - they are very cheap. Check also its series resistor.

This is an extremely simple charger. Nicad chargers usually have a bit more complexity. However, drawing up the circuit as you have described it, I find:

1. The transformer is center tapped. C is the center tap, L and R are the two ends. Given your choice of labels, I think you know this. The two diodes provide full-wave rectification.
2. In this configuration, the voltage that you read beyond the diodes is pretty meaningless, since your meter will read the peaks of the rectified half-waves, not the average or the DC component.
3. The "capacitor" probably isn't a capacitor, since it is in series with the battery being charged. I am assuming it is a low-value resistor, which provides operating voltage for the LED.
4. You should read the color code from the other end - that is, gold-gold-white-blank-gold. But regardless of whether it is cap or resistor, that color code doesn't make sense. I am betting that it is white-brown-gold, which would make it 9.1 ohms. If the entire battery current (180 mA) passed through it, it would drop 1.6 volts, which is not out of line for a LED. Its real purpose is to share some of the charge current with the LED, so the LED doesn't get overdriven.
5. The LED is not expected to light unless a battery is being charged. That is, if you simply plug the charger into the wall and set it on your desk with no battery inserted, the LED won't light. However, if you put something like a 47-ohm resistor across the charger terminals for a moment, the LED should light. Is this what you observe?
6. Hooking up a battery backward will NOT damage the LED due to reverse conduction. The rectifier diodes will prevent current from flowing.
7. Having said that, if you a) short the charger output, or b) insert a battery backward and plug in the charger, it might damage either the LED or the 9.1 ohm resistor or both, due to overcurrent. Assuming that the LED does not light in step 5 above, I'm betting that the 9.1 ohm resistor overheated (which would account for the difficulty in reading the true colors of the bands) and failed open, at which point the LED failed from overcurrent.

Hope this helps. To answer your question "Is it worth spending $100+ to replace this thing", the answer is no. You can replace the LED and the resistor for less than a buck each (Radio Shack). Before you do so, I would recommened using the ohmmeter part of your VOM or DVM to confirm that a) the rectifier diodes are still diodes, b) the 68 ohm resistore is good, c) the LED looks like a diode (or doesn't), and d) the 9.1 ohm resistor is way out of whack (or isn't).

Bil Jeffrey

----------------------------------- snipped-for-privacy@m> Have an OEM battery charger for mid-1980's equipment that does not

snipped-for-privacy@mindspring.com wrote in news: snipped-for-privacy@l77g2000hsb.googlegroups.com:

that's a slow charge rate;must be a trickle charger.

NiCds charge at ~1.5x the pack voltage,usual slow charge rate is 1/10 C,takes several hours,but IMO,NiCds do better with fast charges,1 hr or less.("C"= AH rating,IOW,Capacity.) But for fast charge,you need a temp sensor or a smart IC to monitor cell voltage.

With most trickle chargers,you need to use a timer so you don't OVERcharge the cells,shortening their life.

since your charger outputs a much higher voltage,I suspect the regulating circuit has shorted or failed.

innews: snipped-for-privacy@l77g2000hsb.googlegroups.com:

Its amazing the various replies you got on this problem. Reading your description of the circuit, it sounded like a simple fullwave bridge rectifier circuit converting transformer secondary AC voltage via two discrete diodes with the no "regulation" whatsoever and a light load / power indicator of LED with current limiting resistor. So, if I were you, instead of being gouged by the vendor wanting 120 dollars, find a similar DC wall power supply with output spec near 10-11 VDC ( similar current rating capability) and adapt the power plugs (cut off and rewire the old to new one), and your problem is solved.

Nicads, like someone posted is pretty tolerant to voltage levels, and like to be charged at 1/10th the AH capacity or if you're willing to tolerate it, at even lower charge rate. As far as the LED not lighting up, I would check the LED and the limiting resistor. One of them is probably open circuit. Also, if you hook up 100 ohm load on the output leads, my guess is that the open voltage measurement you got will drop down a few volts closer ot the label voltage rating you mentioned. If the voltage with the load on drops real low, then perhaps you have a shorted winding in the transformer, thus unable to even proved the 100-150 mA charging current.

The fuse thing was a misleading issue, since you miswired it when it happened.

Jim Yanik wrote in news:Xns9929922F6F6C9jyanikkuanet@

Likely Sub-C cells, considering the date. AA cells would be around 600 mAH.

$120 for a replacement charger doesn't seem out of line considering the age and nature of the equipment.

innews: snipped-for-privacy@l77g2000hsb.googlegroups.com:

This is excellent advice assuming you actually measure the resultant charge current. And assuming the power supply does not attempt to power the device, and, and. Last thing you want is a fire due to very poor choice of power brick. It's trivial if you know what you're doing. Not so trivial if you don't. That the question was asked implies the latter.

Better to fix the busted one and remove the risk...assuming you measure the resultant charge current, and, and... mike I claim to know what I'm doing...ask me about my singed eyebrows...

Hello all and again, thanks for your help. I have replaced the LED on the battery charger, hooked it up to the battery pack and the voltage now show 9.42 VDC. I'll let it recharge, but I expect everything to work correctly now.

I am a happy camper and thankful for the advise that this group provided.