Car Audio Power Capacitor PCB Removal Advice

Thread Starter

mr_sd

Joined Jan 9, 2019
3
Hi All! I'm new to the forum so please be gentle!

Question: I would like to know if it is safe to remove the PCB from my power cap.

Background:
I have been using a 1.6F power capacitor for my subwoofer amp (600W RMS) for years. It has a 7-seg voltage display and some control circuitry mounted to the top.

The issue is, I now rarely use my car and when I do, it is for short journeys. It's a 2L Diesel and the battery (100AH Lead Calcium if memory serves) is getting old. The car is now struggling to start in cold weather. I use a regulated solar charger to keep it topped up when practical.

I'm trying to eliminate any sources of current draw while the car is idle. The cap does not have a "Remote" on/off terminal and does not auto power down. Having measured the cap on the bench, connected to a 12V PSU (measuring 12.27V once fully charged), the PCB draws about 60mA while under no external load. (I know that's tiny but if I calculated correctly, it will drain the battery from full in around 90 days and there are other current sources such as alarm etc). With the PCB removed, that drops to 0.02mA when connected to the 12V PSU. When disconnected from the PSU, the cap voltage dropped from 12.27 to 12.20 after 20 minutes of measurement (10MΩ Multimeter).

The PCB is just connected in parallel with the cap terminals (bolted to the top of the cap) It contains:
  • A 7 seg.
  • 1 LED.
  • 1 Piezo Sounder
  • A trimmer for voltage display calibration.
  • L7805CV 5V Regulator
  • LM358N Op Amp
  • CF745 Microcontroller
  • Various small capactiors, resistors and transistors.
As far as I can tell, under normal conditions, the PCB simply serves as a voltage display. When under 11V the sounder activates, under 10V the display shows "Lo" and the sounder continues. It eventually switches off (after a minute or so). When over 15V, the sounder activates and the display shows "HI".

I can't find any circuit diagram online for that particular model and the company who distributed these (American Legacy) is now out of business.

Is it safe to remove the PCB and use the cap without it?
Are there any potential safety features that the PCB might provide that I may have missed?


Apologies if there is not enough info to answer those questions. I will try to draw a circuit diagram if needed but it's black lacquered, so it's a bit of a pain!

Available Specs:
  • Make: American Legacy
  • Model: LCA-160SL
  • Capacitance: 1.6F +/- 5%
  • Surge Voltage 16-20V
  • Temperature: 105C
  • Lowest ESR: <= 0.0016Ω


Thanks in advance,

--

Rich
(Electronics Hobbyist. Ex Maplin Electronics: (RIP). Trainee Network Engineer.)

Images:


 

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MisterBill2

Joined Jan 23, 2018
4,068
My only caution is to be sure to get the polarity correct. That board is strictly an add-on monitor device. The capacitor package will be fine without it.
 

Thread Starter

mr_sd

Joined Jan 9, 2019
3
Superb.Thank you both for your help.

I remember accidentally reversing a 1μF 25V cap in labs while I was at uni. There was a loud bang followed by my favourite smell (slightly burnt PCB lacquer). I can only imagine what that would be like at 1.6F! I've sprayed the positive side of the top of cap bright red to avoid any confusion.

And I'll definitely use a resistive series load of some kind when initially charging.

Thanks again!

Rich.
 
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