Protecting batteries |
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slaz
Old Croc Joined: 27 November 2009 Location: London E2 Status: Offline Points: 2713 |
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Posted: 05 August 2014 at 6:43pm |
A mate pointed out the article in Everyday Practical Electronics Sept 2014 ....
Link to the kit from Jaycar :- http://www.jaycar.co.uk/productView.asp?ID=KC5523&w=KC-5523&form=KEYWORD Might get one for testing ..... one possible problem might be (for us) when voltage across the battery(s) is changing quickly enough to confuse it. I have the EPE magazine here right now .... could scan it I suppose. |
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bitSmasher
Old Croc Joined: 23 June 2012 Location: Melbourne Status: Offline Points: 2295 |
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Hah convenient, I was going to start a thread about battery low voltage indicator/cutoff
This is perfect, and I visit Jaycar in my lunch breaks... will grab one next pay day Shame it can't handle higher current, what options would be out there for 50A+ ? |
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audiomik
Old Croc Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
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Slaz
I designed and built a number of similar devices for use in marine applications some years ago. The purpose of them was to disconnect non-essential loads in steps so that essential things such as navigation lights shouldn't fail due to over discharging the battery. The issue of varying loads causing false sensing is relatively easy to overcome by applying a time constant to the terminal voltage detection and the load currents capability was simply down to the individual circuit's relay rating. Mik |
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slaz
Old Croc Joined: 27 November 2009 Location: London E2 Status: Offline Points: 2713 |
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Mornin Mik ... The business of intermittent current draw (enough to cause the terminal voltage to vary significantly) .... is that what hysterisis means in this context ? |
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audiomik
Old Croc Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
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Slaz
in terms of the detector circuit, yes, sort of. Take for example a fridge motor, the short term inrush current is greater than the running current: so as not to cause 'hunting' then a time delay is applied to the sensing of the battery terminal voltage. Much the same with filament lamps as well, so presumably similar for audio kit. However as the internal impedance of battery cells rise with discharge, then this needs to be included as it also indicates charge state. Makes for an interesting comparator design Thought I might still have one of the PCB's for my design but can't find it..... Mik |
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slaz
Old Croc Joined: 27 November 2009 Location: London E2 Status: Offline Points: 2713 |
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Yup :-) Put a simple, crude ebay LED "digital" voltmeter in the amplifier I use for boombox (which also gets used for mid-tops in bigger rig). This in turm gets used with a 6S LiPo pack for portability mode. and generally with 2 x series 7Ah SLA for static mode. The readout is stable (even when playing flat out) at beginning of discharge cycle, but towards the end of cycle (which is really the bit we're more interested in) - the meter starts getting confused/intermittent .... I have to turn volume right down for a second to get stable readout. Still worth having though. Its a problem I think I'll just live with .... the solution is prolly a bit too complex for me to tackle |
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REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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audiomik
Old Croc Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
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whilst it is raining over the coming weekend, try drawing a graph of the current draw and discharge curve for your batteries.
This then will provide you with a 'nett curve' for battery protection..... Then look at using load current sensing together with battery terminal voltage for improved discharge protection. A Hall effect sensor can easily do your current measurements without inserting any additional impedance into supply cabling. Not too difficult! Mik Edited by audiomik - 06 August 2014 at 8:46am |
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Saturnus
Old Croc Joined: 13 July 2010 Location: Copenhagen Status: Offline Points: 2025 |
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If you like DIYing, www.accusafe.nl has a battery protection kit that handles 8A.
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WesleyK
Registered User Joined: 24 December 2012 Status: Offline Points: 90 |
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And we're currently in the prototype stage for a completely redesigned AccuSafe/batteryprotection system that's completely designed for use with Boomboxes. Better protection, better status indication and just a single momentary button to control all functions. It should handle 12-24V systems, Lead-acid/li-ion/LiFePO4 and up to 15-20A load (to be determined) with upgrades possible to higher current ratings.
Feature suggestions are greatly appreciated :).
Edited by WesleyK - 06 August 2014 at 3:35pm |
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Saturnus
Old Croc Joined: 13 July 2010 Location: Copenhagen Status: Offline Points: 2025 |
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Any chance some of the inspiration for the improved status indication came from me?
Edited by Saturnus - 06 August 2014 at 5:16pm |
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WesleyK
Registered User Joined: 24 December 2012 Status: Offline Points: 90 |
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That's right
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