Taking "Universal Freddy" to the limit....

Competition Time?

Mik Said

The Laird wrote:

Further Work on Ripples

Some pictures of 'scoped waveforms on Freddy.

First is of Freddy powering straight into a ten ohm resistor.

'scope settings are Y=2volts / division
x=5mSec / division
D.C. coupling with wire connections.

So far, so good!

There are more divisions on a single screen with the USB scope. Therefore, rather than setting the V/division value identical to the settings on The Lairds scope, I have to set the V/ screen value the same.

Observation. Mik's 'scoped waveform shows a 'non smooth' wave. The true shape is that on the Tenma 'scope above. The distortions on Mik's waveform is due to the digitising of the signals by the computer system.

The second pair of waveforms

Second is Freddy showing voltage ripple. The ten ohm resistor has been replaced by an eight cell NiMH Vectrix battery block.

'scope settings as above

I cannot figure out how exactly you connected the scope to the charger and battery. The scope seems to show 10V without ripple. So the setting is different from the first one.

The settings are the same as in the first one.

In the first case the 'scope was measuring across the resistor which was attached to the output of Freddy. In the second set the 'scope was measuring across the eight cell battery which was attached to the output of Freddy.

In the third 'scope photo the 'scope settings were as per the previous photo with the exception of the probe coupling which was set to A.C. coupling and the Y sensitivity which was set to 10 millivolts per centimeter (or per division).

If you look carefully you can see the A.C. coupling of the 'scope on the vertical slider control, bottom right of the picture. On the first two pictures the slider is 'down'(the D.C. position) in this one the slider is 'up' (the A.C. position).

There is no 'trick' or 'foul play' going on here. I am simply using the 'scope to it's best advantage to achieve the most accurate results. The 'scope used is a professional 'Tenma' and the rest is down to my engineering skill.

In order to 'scope the output of 'Freddy' which is a balanced output (balanced either side of the mains neutral (essentially an Earth connection) I have removed the 'scope's earth connection. (This is a common and essential engineering practice, but NOT one to be practiced by other than a competent engineer) This allows the body of the 'scope to 'Float' electrically to the potential of the signal being measured. There are many precautions to be taken when carrying out this practice and it can be very dangerous. Again this is not to be attempted by the untrained - you have been warned.
I am an electronics engineer. I know the dangers. Others (non Engineers) may think that they know the dangers BUT they could be mistaken

I will comment again.
'Freddy' is a potentially hazardous piece of equipment and I have previously given warnings of this.

Freddy was designed to do a specific job under specified conditions. I have offered to provide help if anyone has a specific need for a Freddy type circuit, but you have to ask.

I am unhappy about the changes being made as many of these changes bring extra hazards, many of which are not at all obvious to the untrained eye.

The ripple which is put out by Freddy in it's original form and the use for which it is intended are, to the best of my knowledge, harmless to the NiMH battery when used for the occasional 'Equalising' charge. I have, in fact, completely
charged a Vectrix battery from empty to full, using Freddy. I use Freddy on a regular basis, I do not have any problems with this.

I suggest That it is time to stop experimenting with this potentially hazardous piece of equipment. I am seriously concerned that there are people out there reading these pages who may be tempted to try their own 'experiments' with this circuit. I do not wish to see anyone being injured (or worse). I provided a circuit and information freely for anyone of sufficient skill to build and use in comparative safety. I did not intend that others should change or alter it in any way. I asked that anyone requiring something different should contact me via the message system, and I would help sort it out or explain as necessary. That offer still stands but right now I think that it is time to stop the 'public experiments' in the interests of safety.

I am not 'getting at anyone' but I do feel that this topic is in danger of becoming a safety issue. My sincere apologies to anyone who might feel offended by this post. No offence is intended, I am simply putting my cards on the table.

Stay safe and keep smiling:-)

The Laird.

Hi Mik and all interested parties,

Like I said, No offense intended and I hope none is taken.

First, the answers to some questions contained in Miks's post of 24th February.

My results are correct (despite the odd scripting error). It is a matter of connecting the oscilloscope chassis to the reference point of the signals being measured. Without that 'solid' connection there is likely to be all manner of stray signal pickup.

{To see some of these stray signals, just hang a piece of wire on the tip of the 'scope probe and turn up the sensitivity. If you vary the 'scope's timebase you will see a variety of waveforms. It is those that cause the problem and those which must be eliminated.}

Isolating transformers should not be placed between the signal to be measured and the measuring instrument as they can permit stray signals to enter the system.

Digitised oscilloscopes can also introduce distortions on waveforms, a good analogue 'scope does not. It is best to be well acquainted with the vagaries of a digital 'scope before you trust it's output implicitly.

I well appreciate that the needs of individuals will vary, this is why I offered to assist anyone with specific needs. The circuit of the original Freddy was very specific as to it's use, some of the components are present for safety of operation, some are for the safety of the vectrix battery. The procedure for it's use is a part of the safety issue.
If any one item is varied then it can affect the overall operator/equipment safety. Again, I am offering to help anyone with specific needs, just contact me via the message system on this forum.

'Competition time?' was meant to say that there must be an impression by now that there is a competition going on. If such an impression is being given then I don't think that this is helpful to any of us.

The disappearing ripple. When the output of Freddy is connected to a ten ohm resistor, the output shows a D.C. level of 5.0 volts with a 4.0 volts Pk to Pk ripple (which adds to and subtracts from the D.C. level) superimposed on it.

When the output of Freddy is attached to the MiNH eight cell block the voltage ripple disappears ( it doesn't disappear it just shrinks to a mere 10 millivolts) because the battery 'absorbs' the positive peak of the waveform by virtue of accepting the current as a charge The D.C. level is that of the battery voltage.

I have made one error here, for the second waveform without the ripple the Y axis was set to 5.0 volts per division Not the 2.0 volts originally stated. Not that this changes the 'disappearing ripple effect' even slightly. The voltage ripple has not disappeared, of course, it is simply reduced in amplitude and is shown in the next picture as the 10.0 millivolt ripple which it has become.

On the latest part of the post, the use of a resistor for looking at the current ripple.

The six thumbnail shots of the 'scope screen are all, as near as need be, correct.

The stray signals introduced by the digitising process as easily identified and therefore easily ignored. The basic waveshapes show that introducing more resistance into the filter system results in a reduction of the current ripple.

The only comment that I have here is that whilst adding resistance improves the situation, what is really needed to reduce the current ripple is better filtering. This can be achieved by using resistor capacitor combinations or by using inductor capacitor combinations. This principle has already been covered in earlier posts and the principles of filter design have been aired.

The original circuit design provided a minimal filter effect, I was more interested in adding a reservoir (the first capacitor) than the efficiency of the filter (the resistor capacitor combination).

In terms of the observing of the current waveform, the bigger the resistor, the bigger the output and the easier to get a good reliable resulting picture on the 'scope. The voltage waveshape which the 'scope shows is not changed by the resistor value alone (values from 1.0 ohm to 100 ohms could be used in this application). There are provisions/limits to this statement.

The equalising charge It has to be remembered that the need for an equalising charge is brought on by the failure of cells to remain in balance with each other. This problem exists in all cells of all types and all chemistries. The equalising charge is nothing more or less than a purposely applied overcharge to the whole battery which whilst overcharging some cells also allows the out of balance /low charged cells to catch up. The basic principles to be followed are.
1. The level of current should be sufficient to bring the 'low' cells up to full charge in a reasonable time.
2. The level of current should not produce undue heating effects in the 'already full' cells.
3. The equalising current must be greater than the internal losses of the battery.

Cooling a battery (by blowing air across it etc,) to compensate for heat produced by an excessive equalising current and/or charge is doomed to failure. The cells cases might be cool but the cells internals will still be cooking slowly.

Something that has also been hinted at, but not stated in earlier posts, is that because electrical/electronic circuits can be very dangerous, most good design work involves not just producing a working circuit but also looking at every possible source of failure and the consequences of that failure in terms of safety for the operator and also the safety of the equipment and surroundings, any failings found must be designed out, the circuit redrawn and the testing process begun again. In a manufacturing situation this would be followed by prototype testing etc. before a production run could begin

When you buy equipment that fails within it's design life span, you can be sure that the above process has not been applied correctly or you have bought from a sub standard manufacturer/designer/supplier.

I agree with Mik when he says "I understand your concerns about doing this in public. Sometimes I am worried about that, too, and at other times I think it's peoples own fault if they do not heed warnings and get themselves hurt"! In fact I believe that it is time for everyone to take responsibility for themselves and to stop blaming someone else for what boils down to their own personal failings.

Time now to move this designing business off the forum (?). If anyone has specific need, then contact me via the message system and I will do what I can to help.

Take care, stay safe and keep smiling :-)