I was wondering if anybody had any thoughts on whether it is possible to implement powerline communication on a lead-acid battery fed-12V power network.
- voltage: 12 V
- Fed by a battery-bank of 3 X 140 Ah, AGM lead-acid, non-spiral
- typical currents: 2-150 A
- wires: stranded copper 1.5 mm² to 50 mm², PVC isolation
- wires for powerline communication: 30 mm²
- typical wire lengths: upto 30 m
My worry is two-fold:
- will I be able to drive up the voltage in the system to allow communication - or is the battery going to "absorb" it as "charging" current?
- how "noisy" is such a network typically in the frequency range of 133kHz? I.e. how strongly am I likely to have to drive it to enable communication? (The system comprises several 12V DC motors, an alternator, chargers, etc.)
For implementaion I am looking at Cypress CY8CPLC10 and similar.
- Neither the wiring
- nor the DC voltage for power transfer can be changed.
A different way to understand this question is: "What are the ac characteristics of lead-acid batteries in the 100kHz range?"
Update 1: answer to Russel's questions
- required datarate: 500+ baud (I was looking at HART)
- yes, cable length is <30 m. The cabling cannot be touched as all cabling was put in when the structure was built. It is too restricted and convoluted to be able to put in any additional cables. IR is not possible due to no line of sight. RF is an option I am looking at but I was worried about interference with radio equipment on site. Though I realise this is a very real possibility with powerline as well...
- re filters: due to the high currents I was hoping to avoid putting anything in series with the the power carrying line and rely on the digital filters of the modem ICs
- similarly for coupling: at 150A, transformer coupling does not really seem to be a light-weight option. Do you think capacitive coupling is possible here?
- re feasibility of brute force modulation: how do you estimate that a few watts will be sufficient? I am worried about the battery just smoothing any modulation I try to put into the network. In DC conditions a SIGNIFICANT load is required to depress battery voltage by 1V. How easy it is to achieve about 200mV at 130kHz is the big question. I was hoping somebody would tell me: "don't worry about the battery: it's response is much slower than 10µs." :-)