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slaz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2016 at 1:00am
Originally posted by ambientvoid ambientvoid wrote:

ok so iv been looking at different 24v battery options and i found this battery: https://hobbyking.com/en_us/multistar-high-capacity-6s-20000mah-multi-rotor-lipo-pack.html

and i have been looking at amps based on Slaz's suggestions and i found this Sure 2x100watt TK2050 amp: http://store.accusafe.nl/modules/versterkers/sure-2-x-100watt-class-d-audio-amplifier-board

for the battery given the danger of over-discharging lipo is there such a thing as a stand alone inline cutoff module for 6s batteries that could work in a speaker system setup? i've seen a few cutoff modules for smaller batteries but they all seem to rely on signals from an RC ESC unit to work...


Well that amplifier will work fine at 24V - but with 8R loads you'll be getting about 2 x 30W or so - nowhere near 2 x 100W. With relatibely efficient PA speakers e.g. the 2 x titan 8 - it should be about the same volume as my bike box ... and will make for a pretty loud skateboard :-)

But I think the battery is a bit oversized TBH. Should play for about 24 hours :-)
Might be more sensible to get 5-6-7 Ah - which should play the whole day.

I'd recommend building a voltmeter in somewhere (I built one into the amplifer with a momentary contact switch) - then just keep an eye on the voltage every now and then. Stay on yellow alert when the batt voltage gets down to about 22V, and stop using it at 21V.
Conventional wisdom (at least in a commercial product that needs to be pretty much idiot-proof) says use a BMS circuit - but these can be quite troublesome. Do the work of the BMS manually.
Don't let your charger charge up to 4.2V/cell .... the battery will last alot longer (in terms of charge cycles) r if you charge up to about 4.1V/cell - only sacrifices a few percent of capacity.

REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ambientvoid Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2016 at 2:42am
how would it perform on 1 x titan 12 speaker? 
assuming i ask around and manage to find a decent DC-DC up-converter to boost up to the max 32v for that amplifier what gets sacrificed to achieve that extra voltage? and what would that 32v do for the wattage?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2016 at 12:50pm
Originally posted by ambientvoid ambientvoid wrote:

how would it perform on 1 x titan 12 speaker? 
assuming i ask around and manage to find a decent DC-DC up-converter to boost up to the max 32v for that amplifier what gets sacrificed to achieve that extra voltage? and what would that 32v do for the wattage?


Well the DC-DC up-converter is one way, yes, BUT ....

Most DC-DC boards will draw a large current in-rush when you switch on/connect. Strange things can happen when its load is also connected ..... could e.g. blow the fuse between battery and load.
ISTR Sure made one or two DC converters - which may well be better than most, albeit more expensive.

The trade-off in using the DC boards is some loss of battery power - expect a real-world efficiency of about 80-90%.

I have a car laptop power adapter rated at 120W and with a top o/p voltage of 24V (to cater some old Apple laptop that used 24V). This actually works fine for powering my ST508 amp from a 12V lead-acid battery.

But there's another way to achieve your 30V plus .... as long as you're willing to learn about/understand Lithium cells a bit, know your way around your charger, and be willing to baby-sit the batteries during charge. Just get 2 4S packs and make a custom wiring loom that connects the packs in series for discharge, and lets you charge them individually (with your existing charger) by unplugging from the loom.

Or you could, of course, just get a 8S battery pack, but then you'd probably have to get a charger that can deal with 8S .... I think Turningy makes one.

This will achieve about 33V at top charge level - which should in turn get you about 70-80W into a single 8R load (such as 1 x titan 12)  - and that should do nicely.



Edited by slaz - 15 December 2016 at 12:57pm
REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ambientvoid Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2016 at 3:35pm
I'm happy to do 2x 4s batteries, I've found one at half the capacity of the last battery i linked, I realise it's still more play time than I'd likely need but I'd rather have a bit more than I need instead of potentially less.

Unless I'm missing something series wiring doesn't sound that complicated. Would something like this work, where the ends marked 'speed control' would go to the amp?



With maybe xt60 connectors instead of the ones in the picture I could easily disconnect and reconnect the batteries and charge them with my existing charging cable.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2016 at 5:00pm
Originally posted by ambientvoid ambientvoid wrote:

I'm happy to do 2x 4s batteries, I've found one at half the capacity of the last battery i linked, I realise it's still more play time than I'd likely need but I'd rather have a bit more than I need instead of potentially less.

Unless I'm missing something series wiring doesn't sound that complicated. Would something like this work, where the ends marked 'speed control' would go to the amp?

With maybe xt60 connectors instead of the ones in the picture I could easily disconnect and reconnect the batteries and charge them with my existing charging cable.


Yes exactly that (re the cabling). Just make sure you get the right gender of connectors and make solid connections.

The charger will balance the cells within a pack, but you'll need to balance the 2 packs relative to each other manually - thats IMPORTANT ! Vital to distribute the load as equally as possible across the 8 cells.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote ambientvoid Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2016 at 5:04pm
How do I go about balancing the packs to each other?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 15 December 2016 at 7:54pm
Originally posted by ambientvoid ambientvoid wrote:

How do I go about balancing the packs to each other?


Well - you can of course just alow the charger to take the cells up to within 10-20 mV of 4.2 (i.e. "full"), in which case the 2 packs should be quite closely balanced ..... but I now stop charging when cell voltage reaches abut 4.1V/cell  - this achieves considerably better long-term life for the batteries.
(Thats a widely accepted policy ..... I also found this out the hard way :-/ ).

In your case you'd need to manually monitor this - unless - see below :-

One possible way is to tell the charger you have "Li-On" rather than LiPo - most chargers will then "aim for" 4.1V rather than 4.2V - haven't tried this myself - currently investigating this, as I'm not sure if there are any other differences in the charge cycle.
If anyone in here has info on this - please do tell !


REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ambientvoid Quote  Post ReplyReply Direct Link To This Post Posted: 16 December 2016 at 12:58pm
Ah okay, but is there no way of ensuring that the power draw from each battery remains equal during use?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ambientvoid Quote  Post ReplyReply Direct Link To This Post Posted: 23 December 2016 at 12:08pm
As I'll be using my mp3 player as the source will I need a pre-amp or mixer to boost the gain? Are there 24v - 30v pre - amps and if not how do I attach a 12v device into a 28.8v circuit? is there some way i can wire it in so that it is drawing from just one of the 14.4v batteries?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ambientvoid Quote  Post ReplyReply Direct Link To This Post Posted: 29 January 2017 at 3:53pm
My pile so far, im just waiting on the mixer (a gold Omnitronic Gnome-202 Mini) which should arrive sometime next week. In the end i decided that the easiest way of powering a mixer was to run it off separate batteries, the 2 red 12v packs in the picture below, i got a parallel harness for them which will give me a little over 5000mah capacity or about 8 hours run time which should be adequate for me in most circumstances.

A couple of things im missing because im not sure which ones to get are an On/Off switch for the main circuit powering the amp, and a fuse. 
All DC power switches i've seen/used are rated for 12v but obviously this circuit is going to be about 30V to 32V when the batteries are fully charged so im not sure what power rated switch i'll need, an exactly 30/32V switch or something higher for the sake of safety? and i have no idea where id get a switch like that...?
I have absolutely no idea on choosing fuses, i had a fuse in an inline fuse holder on my old 12V speaker but i just used what i was given and luckily it never blew Tongue 


Edited by ambientvoid - 29 January 2017 at 4:15pm
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slaz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2017 at 12:17am
OK - well a coupla things ....

That mixer says 12V DC 500mA on it .... but you may well find it actually uses a good deal less than that - its just that trhe supplied PSU is rated at 500mA. Not using the headphone amp will help with that also. Best to use a multimeter to measure its consumption while in real use, i.e. put signal into it, connect your load (amplifer) .... you well find it uses 200mA or less - in which case 1 of your batteries will power it for a whole day. No point in over-complicating things.

Your switches - don't get too hung up on the ratings - most wil have 1 rating for 230V AC and anothe rfor 12v DC (which will be alot lower) ..... I think you'l find a switch rated at 5A 12V DC will be fine.

Fuse - I'd use about 5A for your main 30V line.

How you gonna build it all together ? The mixer seems like a bit unecessary TBH - although it should give you the gain you need, and likely the tone controls wil be useful.

Which Sure amp module is that you have ?

REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ambientvoid Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2017 at 1:17am
Good to know the mixer might last longer than i thought, i was a little concerned that it might run out before the amp but perhaps it'll be fine now. It might turn out to be unnecessary but id rather have it and not need it than need it and not have it...

It'll be awesome if i can use a 12V switch, it'll make it much easier and cheaper to get (and replace if i ever need to). Thanks for the pointer on the fuse too, hopefully i should be able to pick that up and a switch in town next week.

The amp module is the tk2050 2 x 100w.

i plan to mount a lot of the small electronic bits into padded tupperware type containers screwed into the trailer, this should be especially useful for holding the batteries. im concerned about how to mount the amplifier module though as it has a fan cooler on top of a heatsink and i think putting it in a plastic box wouldn't be good for airflow. From what i've seen online some people mount amp modules in special metal pcb cases where the case acts like an extra large heatsink but i don't know how to do that myself...
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