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slaz View Drop Down
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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 View Drop Down
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Points: 2295 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bitSmasher Quote  Post ReplyReply Direct Link To This Post Posted: 06 August 2014 at 2:19am
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 View Drop Down
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Points: 2962 		Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 06 August 2014 at 7:43am
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 View Drop Down
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Points: 2713 		Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 06 August 2014 at 7:50am
Originally posted by audiomik audiomik wrote:

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


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 View Drop Down
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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 View Drop Down
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Points: 2713 		Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 06 August 2014 at 8:30am
Originally posted by audiomik audiomik wrote:

Slaz

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
Mik


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 LOL
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audiomik View Drop Down
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Points: 2962 		Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 06 August 2014 at 8:40am
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 View Drop Down
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If you like DIYing, www.accusafe.nl has a battery protection kit that handles 8A.
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WesleyK View Drop Down
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Points: 90 		Post Options Post Options   Thanks (0) Thanks(0)   Quote WesleyK Quote  Post ReplyReply Direct Link To This Post Posted: 06 August 2014 at 3:34pm
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 View Drop Down
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Any chance some of the inspiration for the improved status indication came from me? Big smile

Edited by Saturnus - 06 August 2014 at 5:16pm
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WesleyK View Drop Down
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That's right
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