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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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20th Sep 2021, 6:45 pm | #1 |
Heptode
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
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CYCLON battery charging circuit, how does it work ?
This is the circuit from a portable oscilloscope. It charges three 2.5Ah 'D' CYCLON cells.
Can anyone explain the operation of this circuit to me ? Also, it needs a low voltage AC supply from the external transformer, but what voltage would you suggest ? Thanks, Buzby |
20th Sep 2021, 7:42 pm | #2 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
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Re: CYCLON battery charging circuit, how does it work ?
Possibly 6V AC ?
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20th Sep 2021, 9:15 pm | #3 |
Nonode
Join Date: Aug 2007
Location: South Bradford, West Yorkshire, UK.
Posts: 2,573
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Re: CYCLON battery charging circuit, how does it work ?
The TL431 is a "programmable zener". The voltage at the slider of the pot is 2.5V which gives the voltage at the base of the transistor a range of 3.56V to 4.28V with the voltage at the emitter approximately 0.65V lower (2.9V to 3.6V) which seems a bit too low for charging 3 Cyclon cells.
Keith |
20th Sep 2021, 9:16 pm | #4 |
Hexode
Join Date: Oct 2010
Location: Box End, Beds. UK.
Posts: 271
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Re: CYCLON battery charging circuit, how does it work ?
The 431 and its associated resistors form a voltage reference, and the transistor is an emitter follower from that. Note that there is no smoothing capacitor, so the output will be a series of voltage regulated pulses.
I think cyclons are lead acid technology, so around 2V3 or 2V4 per cell on charge, so around 7 volts across the cells, a few volts of loss in the regulator, so need 10V or so (plus a bit maybe) out of the rectifier, call it 12V peak into the rectifier gives around 8 to 9 V RMS out of the transformer. Note that there is no current limiting other than the fuse, which may not be ideal Disclaimer - I haven't done any calculations on the circuit so I don't know what voltage it is likely to actually produce Last edited by trsomian; 20th Sep 2021 at 9:18 pm. Reason: Further thoughts |
20th Sep 2021, 9:30 pm | #5 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
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Re: CYCLON battery charging circuit, how does it work ?
The battery charger regulator is a simple emitter follower pass transistor with its base voltage controlled by the programmable "zener" VR1. It's doubly "odd" in that it looks upside down and it's fed with unsmoothed full wave rectified dc so the battery will see a series of voltage pulses each peak limited at the level set by the regulator minus the Vbe of the pass transistor. There may be unseen "tricks" to doing it this way, perhaps wrt charging voltage temperature compensation or it may just be the quick'n'dirty design that it appears to be. It does save the cost of an (unreliable) electrolyticsmoothing capacitor though?....
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20th Sep 2021, 9:48 pm | #6 | |
Dekatron
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Re: CYCLON battery charging circuit, how does it work ?
Quote:
You get the odd figures above if you transpose the values for the programming resistors in the the app note equation Vout = Vref*(1+R1/R2).
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20th Sep 2021, 9:55 pm | #7 |
Nonode
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
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Re: CYCLON battery charging circuit, how does it work ?
To trickle charge three cells in series, you need 2.203v per cell, a little more for faster charging. Obviously a Tek circuit. As already pointed out, no capacitors, but the cells are in effect one large capacitor. Taking a 4.8v secondary, Xs 1.414, we get 6.9v, so no more than 5v secondary surely?
les. |
20th Sep 2021, 10:24 pm | #8 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
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Re: CYCLON battery charging circuit, how does it work ?
I would expect a somewhat higher ac than 5V- the regulator effectively clamps the peak voltage at the charging voltage for the battery so the higher the input ac, the more of each half cycle is useful to charge the battery. An upper limit would be set by the dissipation limit for the pass transistor but a guesstimate might be that ac input that makes perhaps 25-50% of the half cycle "useful"
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20th Sep 2021, 10:29 pm | #9 | ||
Nonode
Join Date: Aug 2007
Location: South Bradford, West Yorkshire, UK.
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Re: CYCLON battery charging circuit, how does it work ?
Quote:
Keith |
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20th Sep 2021, 10:37 pm | #10 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
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Re: CYCLON battery charging circuit, how does it work ?
1. Must work when mains is 10% low
2. double diode loss in bridge rectifier That would suggest transformer nominal output closer to 6.5V min. |
21st Sep 2021, 12:09 am | #11 |
Moderator
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Re: CYCLON battery charging circuit, how does it work ?
Using 'dirty DC' is an old trick considered to prolong battery life over more charge/discharge cycles. Sometimes used with all sorts of cell chemistry
David
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21st Sep 2021, 8:50 am | #12 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
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Re: CYCLON battery charging circuit, how does it work ?
Ahh- I'd come across dirty DC as a good idea for NiCads but not encountered it (except incidentally in old car battery chargers) as being a benefit for PbSO4.
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21st Sep 2021, 10:07 am | #13 |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
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Re: CYCLON battery charging circuit, how does it work ?
Here is a snip from the CYCLON data sheet. Re constant voltage charging.
It suggests a range of 2.3 - 2.5 volts per cell depending on trickle or fast charge. I see the circuit as a simple voltage regulator. And likely set to a suitable charge voltage as long as the pot (R112) has not been twiddled? You need a transformer that exceeds the double diode drop and pass transistor drop, so about 9 volts. Data sheet here: https://docs.rs-online.com/c7b6/0900766b800278eb.pdf
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21st Sep 2021, 1:48 pm | #14 |
Heptode
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
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Re: CYCLON battery charging circuit, how does it work ?
For a bit more info, here is the PSU circuit.
Regarding the batteries, I took the pack out and put it on a 7.3v Constant voltage supply. Left it running all night. The current drawn varied started at 1.25A, and finished at 0.8A. Battery voltage tests now at 6.25v, but it won't drive the 'scope. Tried a 7.3v supply in place of the battery pack, and the 'scope works fine. It works fine down to about 6.6v, so I think the cyclons are dead !. I can't test the charging side of things until I find a suitable AC PSU. ( I did have one, it came with the 'scope, but that was twenty years ago ! ) Cheers, Buzby |
21st Sep 2021, 2:51 pm | #15 |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
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Re: CYCLON battery charging circuit, how does it work ?
Just an observation, normal lead acid cells give about 2.1 volts off load and charged, so best possible output from 3 cells will be 6.3 volts. Less as soon as a load is applied.
Before drawing any conclusion about the Cyclons, you need to establish if the scope works from a solid 6 volt (or even 5.5 volt) supply.
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21st Sep 2021, 3:17 pm | #16 | |
Heptode
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
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Re: CYCLON battery charging circuit, how does it work ?
Quote:
The manual describes how to set the PSU shutdown voltage, and it seems to require shutdown when the supply from the battery is below 5.75v, which is 1.92v per cell My quick experiment earlier showed shutdown at around 6.6v, so that doesn't look right. I'll be back to investigate further after mowing the lawn !. |
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21st Sep 2021, 10:52 pm | #17 |
Heptode
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
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Re: CYCLON battery charging circuit, how does it work ?
After mowing the lawn I did a bit more testing.
It definitely looks like the shutdown circuit was set too high. The scope is now running off the cyclons, at 6.07v at the moment. Spec says it should run for three hours on battery. I'll check that tomorrow. Cheers, Buzby |