RCMW DIY Multi Output Charger

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Spike S
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Re: RCMW DIY Multi Output Charger

Post by Spike S »

Igull wrote: 09 Sep 2018, 19:42 It is a known fact that using raw DC to charge nicads cleared the dreaded dendrite growth problem
Neil
I'm intrigued, especially where our rechargeable batteries are involved.
"Pulsed DC", "Half-wave-rectified DC", "Constant-Current DC", "Constant-Voltage DC" I understand.

What is meant by "Raw DC". How does it differ from "DC" ? :?
Spike S
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Martin
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Re: RCMW DIY Multi Output Charger

Post by Martin »

After a quick look at the PCB, it seems to me that the circuit just consists of 6 identical half-wave rectifiers. Three of the rectifiers: Rx1, Rx3, Tx1 work on one half wave and the other three: Rx2, Rx4, Tx2 work on the other. Each of the rectifier circuits consists just of a diode, a resistance, and an LED. There is a switch that switches different resistors into the resistance and so varies the charging current.

What surprises me - and perhaps I've missed something - is that the 'transmitter' 9.6V rectifiers are identical (save having different resistances) to the 4.8V 'receiver' rectifiers. Both types are just half-wave rectifying the AC voltage coming from a 15V transformer wiring. So you could charge a transmitter battery from one of the receiver connectors and it would still charge up fully - just taking a bit longer because of the higher resistance.

In terms of the charging current, it's a pulse-charger. The pulses come every 20 milliseconds and last for rather less than 50% of the whole cycle (just how much less depends on how much higher the peak voltage of the unloaded AC is, compared to the voltage of the battery on charge). If I'm right about the same circuit and transformer winding being used for both receiver and transmitter batteries, then the transmitter batteries will be charged with shorter pulses, occupying a smaller fraction of the total time, than the receiver batteries.
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Igull
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Re: RCMW DIY Multi Output Charger

Post by Igull »

Spike S wrote: 10 Sep 2018, 07:24 What is meant by "Raw DC". How does it differ from "DC" ? :?
Just DC that hasn't been smoothed with a capacitor - either half or fullwave rectified from (say) a mains transformer- lots of lovely ripple :)

This in the days before microcontrollers that could easily modulate/pulse anything. Also, most PSU's (for the DIY Joe Public at least) were non-switched - just analog(ue). Not that you need a microcontroller to do it, just makes it easier.

Cheers

Neil
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Igull
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Re: RCMW DIY Multi Output Charger

Post by Igull »

Martin wrote: 10 Sep 2018, 11:57 What surprises me - and perhaps I've missed something - is that the 'transmitter' 9.6V rectifiers are identical (save having different resistances) to the 4.8V 'receiver' rectifiers. Both types are just half-wave rectifying the AC voltage coming from a 15V transformer wiring. So you could charge a transmitter battery from one of the receiver connectors and it would still charge up fully - just taking a bit longer because of the higher resistance.
Yes, 20th century constant current ('ish) which was the 'preferred' charge method at the time (yes, I know it's not constant :-) ) - lots of nonsense about 'nicad memory' - based on some drivel from NASA satellite data - many people made mucho dollars on that platform :lol:
In terms of the charging current, it's a pulse-charger. The pulses come every 20 milliseconds and last for rather less than 50% of the whole cycle (just how much less depends on how much higher the peak voltage of the unloaded AC is, compared to the voltage of the battery on charge). If I'm right about the same circuit and transformer winding being used for both receiver and transmitter batteries, then the transmitter batteries will be charged with shorter pulses, occupying a smaller fraction of the total time, than the receiver batteries.
? It's still half-wave, so 50Hz - 20mS - full wave would give you 100Hz 10mS AFAICS.

Cheers

Neil
Martin
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Re: RCMW DIY Multi Output Charger

Post by Martin »

Yes, still 20 ms pulse spacing, but the charge current only flows when the half-wave voltage exceeds the battery voltage. With a 4.8V battery on charge this will be perhaps 25% of the whole cycle time, but with a 9.6V battery on charge it will only be about 10% of the whole cycle time because only the topmost part of each peak is higher than the battery voltage.

I've scribbled and photographed something as it's difficult to explain just with words but no pictures.

halfwave.jpg
Last edited by Martin on 11 Sep 2018, 12:06, edited 2 times in total.
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Mike_K
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Re: RCMW DIY Multi Output Charger

Post by Mike_K »

Hi Neil

The design was perfect for the NiCad's of the 80's, why have a full wave rectifier when a diode would work just as well. A current limiting resistor is far simpler than a voltage regulator. And who needs smoothing caps, a NiCad does just a good a job of that.

But since then things have moved on a bit. Back then we were using 500mAH NiCad's, so a charger with a 50mA current would fully charge a flat battery in around 10 hours. When fully charged, the NiCad would easily dissipate the heat given off (50mA x 1.55V = 77.5 mW), so no cut-off circuit was required.

Fast forward to today and we are either using lithium based batteries with a UBEC or a NiMH battery, probably of 2000mA capacity or greater. For most of my sports models I use Panasonic Eneloop 2000mAH batteries. But the load on them is far higher than in the 80's as I have more servo's (typically 2x ailerons and flaps) and they are usually digital. And I don't recharge every session if I've only had a couple of flights. So when I come to recharge I probably need to put back 1,000 to 1,500 mAH of charge and I don't want to take all weekend charging at 50mA. But at least you shouldn't damage the battery at that charge rate, Panasonic recommends that the maximum trickle charge rate at 0.05C = 100mA for a 2000mAH Eneloop and their own chargers trickle charge at 50mA (when the fast charge is complete).

But why not invest in a modern charger? They nearly all use PWM for current control, so you still get you pulsed charging, albeit at a higher frequency. You can still slow charge if you want or if in a hurry do a quick charge. Better still you can occasionally do a full discharge - charge cycle to see their true capacity which is a good indication if they're still up to the job. And they're not much more expensive to buy than building your own geriatric charger© (I think I should Copyright that name :D )

Cheers

Mike
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Igull
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Re: RCMW DIY Multi Output Charger

Post by Igull »

Mike_K wrote: 11 Sep 2018, 11:17 But why not invest in a modern charger? They nearly all use PWM for current control, so you still get you pulsed charging, albeit at a higher frequency. You can still slow charge if you want or if in a hurry do a quick charge. Better still you can occasionally do a full discharge - charge cycle to see their true capacity which is a good indication if they're still up to the job. And they're not much more expensive to buy than building your own geriatric charger© (I think I should Copyright that name :D )
You mean like this lot on my charging station :lol:

20180911_195318.jpg

These el cheapo 4 button chargers have sufficed for a number of years - built in PSU's too - or DC 12v. The main thing is that they're separate and NOT a multi charger which is one down all down :?

I also have 2 ISDT Q6 lite chargers for other odd jobs and a few DIY pulse chargers I made some years ago plus there's at least one old astroflight 110D in the garage that charges some odd things too - and of course, my Geriatric Charger (tm) for my slopers :D

Cheers

Neil
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Igull
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Re: RCMW DIY Multi Output Charger

Post by Igull »

Martin wrote: 10 Sep 2018, 22:07 Yes, still 20 ms pulse spacing, but the charge current only flows when the half-wave voltage exceeds the battery voltage. With a 4.8V battery on charge this will be perhaps 25% of the whole cycle time, but with a 9.6V battery on charge it will only be about 10% of the whole cycle time because only the topmost part of each peak is higher than the battery voltage.
I've scribbled and photographed something as it's difficult to explain just with words but no pictures.
Yep, that all looks about right :lol:
I think the 'shorter pulses' you mentioned were really ones of lower amplitude rather than shorter period :)
This is all getting far too complicated for my toy aeroplanes and aging brain :lol:

Cheers

Neil
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Mike_K
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Re: RCMW DIY Multi Output Charger

Post by Mike_K »

Hi Neil

You mean to say you want to build a geriatric charger® when you have all them modern ones lined up, what a silly idea. Next thing you'll be suggesting is that we take vintage transmitters from the 60's and 70's, convert them by fitting modern guts and 2.4GHz modules and then fly with them. Oh hold on...

You'll probably not be interested to know that I've got a boat lined up for the 1950's ED S/C set I bought from you, complete with ED Boomerang Rx, ED motorised escapement and an ED Racer Marine diesel (home converted by a modeller in the 50's to be water cooled). And 8 feet (4x 2ft) of best B&Q aluminium tube for the aerial. The set works remarkably well considering it's age, but can I get the engine to run properly. So I'm probably not the best person to be lecturing you about not using 1980's electronic designs when I'm dabbling with and planning to use a 1950's radio :)

Cheers

Mike
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Igull
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Re: RCMW DIY Multi Output Charger

Post by Igull »

Like the idea of a boat, I've had the plans for a KK Sea Scout for a few years with a view to making one - I even have a real DC brushed electric motor for it ! I'm sad to say that I've never actually built a boat (except for a wee model yacht from a lump of pine for my granddaughter :-) )

I was producing clones of the Veron Crash Tenders - by Kitshack for a while, but that seems to have died off. I considered making one for myself, but too interested in aeros really :-)
I did do a couple of very large laser cut 'kits' for a mould producer in the Bahamas - they were for these hyooge model racing boats - absolutely stunning when finished.

Look forward to seeing some (grainy and sepia toned :-) ) videos with you at the side of the loch complete with bedside lamp pushbutton in one hand and pipe in the other a la col. taplin :-)

Cheers

Neil
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