Horn wiring issue

[Fjp]

Hello Everyone,
I recently completed a conversion on a Trident Trekker and directly wired a 48 volt car horn To a 48v 17.5 ah bafang battery. The led lights are also wired direct to the battery and work perfectly. The horn has an intermittent problem. On occasion, it will shut down the system.... screen goes blank. If I cycle the battery on-off switch the system will restart. I’d like to figure out what I did wrong because the horn works pretty good on car traffic. Please see pic and wiring diagram below. Any ideas?
Thank you,
Frank

 

[Chalo]

Your system is probably vulnerable to electrical noise and voltage spikes, which your horn is good at making.

Others have suggested putting a choke on the power cable to your horn, which seems like an easy first thing to try.

 

[Fjp]

Hi Chalo,
Thank you fir the response! I’m not sure what a choke is?
Thank you,
Frank

 

[LewTwo]

Your system is probably vulnerable to electrical noise and voltage spikes, which your horn is good at making.

and I thought the whole point of a horn was to produce noise :wink:

 

[E-HP]

Hi Chalo,
Thank you fir the response! I’m not sure what a choke is?
Thank you,
Frank

A choke circuit could be as simple as an inductor (coil), or could include inductors and capacitors. The simplest would be ferrite beads that clamp around a conductor (those little barrels that are sometimes around a power supply cable). They attenuate/block signals based on their frequency, while letting others pass. Your car or home stereo speakers' crossovers, for instance, will have coils that allow low frequency signals to go to the woofers, but block the higher frequency signals.

A car horn has frequencies typically in the 300-600hz range, which may be interfering with the BMS and causing it to trip, not on low voltage or high current, but due to the noise introduced to the battery wires by the horn. The right sized choke could reduce that noise. I believe that's what Chalo is referring to.

 

[Fjp]

Thanks guys,
I’m going to see what I can find that may do the job. I’m also thinking of swapping the 48volt horn for a 12 volt and installing a step down transformer (useful for other accessories too). Any idea if that may work?
Cheers,
Frank

 

[amberwolf]

If you do, the 12V DC-DC will have to supply the full current that the horn will take when initiated, which can be a few dozen amps initially (even if it is "rated" for much much lower). If it is not, it may either shutdown just like your present system, or it may even fail.

Putting a choke on the power wires to your present horn is probably the simplest and cheapest option. If it helps, there are a number of videos, pages, etc., here: https://www.google.com/search?q=how+to+make+a+choke+-carb though I don't know which one will best suit your DIY level.

 

[Fjp]

You guys are indispensable!
Thank you for taking your time to help out,
Frank