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Higher voltage?

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kipman725 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Topic: Higher voltage?
    Posted: 02 September 2020 at 1:56pm
I built a 16S 20aH Lion battery for my portable setup (60.8 - 67.2V) and wonder if anyone else is also running on higher voltage?

I'm using TI TPA series chip amps and a buck converter to take the DC bus down to 36V.  Running at just below the onset of clipping into 100dB/1w mains (4 amp channels no subs) for 6 hrs reduced battery state of charge from 100% to 80%.

I have also adapted a Numark DJmix pro mixer to run from 36 - 74Vdc by taking out the existing power supply and replacing it with isolated DC-DC converters.

The rational for going this way rather than 12V or 24V was to reduce idle losses, idle current for the whole system (amps, DSP, mixer) is 0.2 - 0.3A.  When I have some more time I want to develop my own amps that run directly without needing the buck converter for more power and to reduce the size of the amp box.   I would also like to be able to run SPDIF from the mixer to the DSP however that's not possible with the current DSP as it lacks an ASRC so making my own DSP board is something I would also like to do.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jo bg Quote  Post ReplyReply Direct Link To This Post Posted: 02 September 2020 at 2:47pm
Very nice, the mixer mod in particular!higher voltage makes plenty sense,
Only problem is you are depending on your custom battery; a 24v rig could run with a couple car batteries, easy to find in emergencies.
But your battery pack seems to last already long.
Are you on Diyaudio? I maybe remember your nick... welcome on the board!
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kipman725 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 02 September 2020 at 5:00pm
Yep I'm also on DiyAudio.  I bought the mixer with a failed power supply (blown up filter cap).  I then traced out the existing circuit and found it needed 5V for the digital supply and +/-15V for the analog supply, I removed the existing linear regs and replaced them with high input voltage isolated converters.  I would have kept the linear regs on the analog supply and fed in a higher voltage like +/-18V but I couldn't find any suitable converters.  In the end I don't notice any noise running the analog directly off the switcher.  Externally the mixer looks stock apart from labels I have added indicating the input is now 35 -74V DC over the old AC input labels.

Battery seems like it would last all weekend if needed, adding solar would be the way I would go about extending it.  I wanted ultra portability so lead acid would have been too heavy.  I'm working on some more compact speakers to pair with the amp setup.  I have 2*12tbx100 that I have designed compact reflex enclosures for and am attempting to merge a 12" midbass with a B52horn to make a compact unity horn.  I need to do more complicated simulations of the latter idea than Hornresp supports as I want to use an expanding duct to bring in the midbass to the horn to maximise bandwidth of the midbass.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 02 September 2020 at 6:11pm
Sure, makes total sense! Of course! the lower your discharge current the more capacity you can use, so given that, higher voltage packs should indeed result in better efficiency (play time per charge). 

As the price of lithium cells comes down more and more people will probably move to higher voltage low voltage rigs. I mean right now I can buy Samsung 2200mAh 18650's for £2.13 each, MOQ 20. That's only likely to get less and less, and if you are able to buy/import from USA there are deals like 2x18650 in a case for $1.50 (industrial surplus). 

Just remember, kids, if the voltage is over 50v, it's not "safe extra low voltage" any more - so you should pay extra attention to the voltage ratings of your components, and to electrical safety in general. For example, car blade fuses are only rated to break 32v, so you should use something else like a 1.25 inch glass fuse. Most of the common connectors are rated to over 50v, but spade terminals and crimps are not (32v again). You can't have any bare terminals, everything needs a box. Some yellow stickers warning of voltage over 50v wouldn't go amiss.

I would also use quite a funky connector on your battery output, just so there's zero chance of accidentally plugging it into something that's expecting 12 or 24v. EG a 4 pin XLR or similar. 
Studio45 - Box Builder Commotion Soundsystem -Mobile PA
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 09 September 2020 at 12:00pm
Yes its worth mentioning that a 16S lion pack is outside of "safe extra low voltage" so if your making something for use by other people you need to make sure that its double insulated which is obviously not the case with my prototype.  However all the connectors are correctly rated and there is a DC over current circuit breaker used on the input in addition to the BMS in the battery pack having a current limit function.  There are a few issues though; firstly the DC circuit breaker would trip on connection of the battery due to charging the input caps on the DC-DC converter and secondly when load testing the battery into a restive load I was unable to disconnect the load without damaging a connector due to arcing.  To solve the first issue I put a small power resistor in line with the power input (a bit of a hack).  The second issue shows I should have installed a DC breaker on the battery pack so I could disconnect it without having to pull a connector pair apart.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 09 September 2020 at 12:57pm
Originally posted by studio45 studio45 wrote:

I would also use quite a funky connector on your battery output, just so there's zero chance of accidentally plugging it into something that's expecting 12 or 24v. EG a 4 pin XLR or similar. 


Whoops ... to me, 4-pin XLR _implies_ 12V. In my days of using/maintaining industrial video gear (in the last century :-) ), most of the "field use" gear e.g. cameras, field monitors, portable VTR's etc. used 4-pin XLR for power - and _all_ of it was 12V (well, 12V nominal).

In fact I picked up a converted car starter thang - just used as a  carry case really for a 12V 18Ah SLA battery - - they'd taken out the main high current croc-clip cables and fitted 2 x 4-pin female XLR connectors. Definitely for use in field video recording.
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 kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 09 September 2020 at 3:12pm
I used XT90 as the BMS is set to limit at 50A so all cables and connectors need to be rated to that current.   However I think if you tried hard with your little finger you could get a shock so I would use a shuttered connector, however I'm not aware of a commonly available connector that would be >50A up to 70V and shuttered.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic the hedge Quote  Post ReplyReply Direct Link To This Post Posted: 09 September 2020 at 7:50pm
Originally posted by kipman725 kipman725 wrote:

I used XT90 as the BMS is set to limit at 50A so all cables and connectors need to be rated to that current.   However I think if you tried hard with your little finger you could get a shock so I would use a shuttered connector, however I'm not aware of a commonly available connector that would be >50A up to 70V and shuttered.

Anderson powerpole connectors would be ideal, not shuttered but touch proof, rated 600v. Available in a range of sizes up to 350A IIRC
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 09 September 2020 at 10:06pm
I found some amp modules that ran off 48V volts and successfully ran them off four leisure batteries. can't remember the name now but must be in the lockup somewhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2020 at 12:08am
Sure electronics do some amp modules that could run directly off the battery but they are quite expensive and have ~20W idle power consumption:
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Post Options Post Options   Thanks (1) Thanks(1)   Quote jonaglon Quote  Post ReplyReply Direct Link To This Post Posted: 27 September 2020 at 7:21pm
I've used a 20ah 48v lifePo4  eScooter battery and several of the Sure 48v amplifiers (or similar bought with varying success directly from China) to make a test sound system. The amps are running on 36v using multiple buck converters, they couldn't take 48v. I used a couple of 4 ohm 12" drivers built into postage tubes , then built them into unsuspicious looking holdalls to make a "portable" sound system. There are ports under zips at the back of the speaker duffle bags. The battery / amp holdall is heavy, other two not too bad, the tweeters pack into the speaker duffle bags. There's a miniDsp for the x-over (powered with a handy 5v out on one of the amps) which I also use to add quite a lot of EQ, helping I think to compensate for the weird nature of the enclosures. I've not had a proper chance to test it but sounds pretty pokey for a battery powered system so far. It needed a ground loop isolater but sounds clearer than I'd hoped for after I'd added that.



Edited by jonaglon - 27 September 2020 at 7:31pm
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kipman725 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 27 September 2020 at 11:21pm
very incognito setup, drop the bags drop the bass.

I have been looking at the IR4301 to make a higher power chip amp:
it can take the voltage and just seems to be thermally limited but if you check out the app notes they didn't try very hard to get the heat out and still hit >100W power levels.  I think if I use Alu core inserts in my PCB and bridged the chips I would stand a chance of ~500W/channel.  Lots of projects ATM though I have to clear before getting onto that.
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