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12v bike trailer system (help needed)

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Goegon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goegon Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 1:37pm
Thank you so much for this really helpful post Slaz!
I feel like it's starting to come together.

I'll use a tham12 loaded with a B&C 12NDL76 because of it's 100Db sensitivity.
Then as you suggested the ZX1-90 8" because it's the lightest i can find.

A suitable car amp i found is the Alpine KTP-445A. it's a 4 channel amp with 45Watt per channel at 4 ohm, so that should give me enough power when i bridge it i think.
That amp doesn't have eq / filters as far as i see but a friend said he'll help me with making a passive crossover for the sub/mid. So let's see if that works out :)

For the battery i think i'll buy a VLRA 110Ah gel battery, should last me long enough if i don't cranck it up.

Will that + a circuit breaker for safety have me settled? Any other things i must consider? Like i heard you need to use thick wiring etc... Anything a noob like me might forget! LOL


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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 2:13pm
About car amplifiers in general .... they're nearly always rated with a supply of 14.6 V or so (as from the car's alternator/charging system) - but when you're using it as stand-alone, your mean supply voltage is more like 12.5V (starting from just over 13V and dropping to about 11.5V at end of discharge cycle. So because power relates to square of voltage, that equates to about 70% of the rated power.

So your 90W of bridged power is actaully about 65W.

I'm pretty sure Pioneer does an amp with 4 x 80W -> 4R or so .... worth having a bit more headroom with about 2 x 120W.

Oh yeah - another thought ....
If you have mains power close to where you're gonna store the rig - no problem, but if you have to lift the battery out to charge it, you (well, your back) will start cursing it pretty soon. Try to make everything easy-ish to remove from the rig for testing/trouble-shooting purposes.


Edited by slaz - 29 July 2019 at 2:19pm
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 markie Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 2:18pm
Passive crossover from sub to mid is not a good idea. To get even close to good performance you'll need a huge inductor, expensive caps, and it won't even be close results wise to an active. You'll lose a lot of your already limited power.

Passive mid/top is fine, passive sub/mid, don't waste your time.


Edited by markie - 29 July 2019 at 2:19pm
If it's got wheels or tits it's gonna cost a fortune
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 2:18pm
I'd also look at smaller batteries than a 110Ah monster. I stoat about with little 16Ah units, like you'd get in a mobility scooter or golf trolley. I carry one spare in my pannier, and I've never run out of juice in the middle of a gig yet! 
A 110Ah is 25kg on its own - you want to try and keep your trailer weight below 50kg, so that doesn't leave a lot of weight for wood and drivers...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 2:39pm
Good point. Try to make your system accomodtae (in some way) different size/shapes of batteries.
See if you can rope your mates into carrying extra batteries on their bikes !

Incorporate a voltmeter into your amplifier setup so you can keep an eye on it.
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 Goegon Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 2:51pm
Originally posted by studio45 studio45 wrote:

I'd also look at smaller batteries than a 110Ah monster. I stoat about with little 16Ah units, like you'd get in a mobility scooter or golf trolley. I carry one spare in my pannier, and I've never run out of juice in the middle of a gig yet! 
A 110Ah is 25kg on its own - you want to try and keep your trailer weight below 50kg, so that doesn't leave a lot of weight for wood and drivers...


I was worried about the running time but maybe unrightfully so.
But running at 100 watt on a 16Ah will give me close to 1 hour according to https://mbharris.co.uk/12-volt-sound-system-battery-calculator/ (?)
I plan on using this for small free parties, i'd like to get at least 6 hours out of it...
I had a limit of 80kg in mind, i won't be partying alone so i could switch bikes with a friend if it gets too tiresome. Maybe I'm being unrealistic. But you think 2 x 16Ah batteries will get me to 6-8 hours?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote markie Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 3:19pm
Bear in mind that the online calculator assumes a continuous load. Music is not continuous. Every time the kick drum comes through you will be on peak load, but in between each beat the load will be considerably less. The actual time  (depending on music content0 will possibly be 2/3 times as long as if the load was continuous.
If it's got wheels or tits it's gonna cost a fortune
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 4:16pm
Originally posted by markie markie wrote:

Passive crossover from sub to mid is not a good idea. To get even close to good performance you'll need a huge inductor, expensive caps, and it won't even be close results wise to an active. You'll lose a lot of your already limited power.

Passive mid/top is fine, passive sub/mid, don't waste your time.



You can get around that by putting the filter set for the sub channel(s) before the amp, instead of in the sub. Same for the HPF on the passive mid-high channels.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 6:32pm
As in "passive line level"? Probably not a good idea for 12v applications, as there's always some insertion loss with passive filters and you're usually struggling for enough signal level from the source anyway! Could use gain blocks to get it back of course, but that means extra hissssss
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 7:06pm
Most stereo information is in the mid range, so you could use one output for sub, 1 output for both the 1" drivers in the coax and use the remaining 2 outputs for stereo left and right from the 8" Beyma's.

Alternatively you could use a passive filter for the 8"/1" coax (~ 2.5 kHz) then use 1 output of the miniDSP for the sub, 2 outputs for the 2 coax tops and the remaining output for the intended slot tweeter (personally wouldn't use those) or as monitor.
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