John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp | reply to pmurdock
Re: hub or switch at solar powered POP?
What is your system voltage?
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A is A |
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pmurdock
Paul Murdock
join:2001-09-13
Riverton, UT
1 edit | It will be run from a 12V sealed gel cell 285 Amp/hour battery that is charged by some photovoltaic cells.. So the 7.5 v supply is better than the 10V minimum requirement.. however 52 mA versus 300 mA doesn't make sense.. well the equation makes sense.. 
for 52 mA switch
P = IV
2 watts = (I)*10 volts -> I = 2/10 -> I = 0.2 amps
for ~300 mA switch
P = IV
1.5 watts = (I)*7.5 volts -> I = 1.5/7.5 -> I = 0.2
so it appears that the parvus one is better.. though 200 mA is a horrible draw to have for both of the switches..  is that a continuous draw..?
I would think that the draw would be higher at a higher voltage since voltage is like "pressure" if you applying a higher pressure more current would want to flow through the system. So why only draw 52 mA @ 24VDC and draw MORE current (~200 mA) @ 10VDC? This is what I don't see.
cheers,
Paul |
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Semaphore
Premium
join:2003-11-18
Arnprior On.
| reply to pmurdock
If the required layout is that two devices need to talk to one device then a passive Ethernet splitter would work. Yes they make them. I haven't installed one in over a year but they allow two PC's to share a single Ethernet drop. You can't get Full Duplex but you can get 100Mbps. Yes collisions are problem. No the to devices can't talk to each other directly. Ugly but it does "work". |
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pmurdock
Paul Murdock
join:2001-09-13
Riverton, UT
3 edits | Ok.. so what we have is the new device - the battery voltage device will only ever be active for 5 seconds each hour to transmit it's voltage back to the data center.. So in essence I guess the two devices never need to talk to each other. Here is a drawing that I have made to represent the design..
Basically what will happen is a server in the NOC will send out a UDP request to the battery monitor asking for it to send back the voltage every hour. It will only need to respond with a very small packet and then go back to sleep (drawing microamps current - now that is what I call small! )
Bear in mind also this is a far-away repeater in the middle of nowhere.. with a very limited potential client base.. I'd be happy with a 1Mbps connection to this location and not worry about saturation..
cheers,
Paul |
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cmaenginsb
Premium,MVM
join:2001-03-19
Palmdale, CA
| reply to pmurdock
Well you can try it and tell us how the idea works.
As to current, higher voltage is not higher "pressure" many people tend to make this mistake.
Instead to understand the equations think this way, Watts is a payload of sand. Voltage is the number of dumptrucks you have to carry the sand. Amperage is the number of trips they make.
If the amount of sand stays constant if you increase the number of dumptrucks it will take less trips. The relationship between volts and amps is similiar. Amperage is a function not of things being forced but how much energy the device needs to operate. |
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nwn
Premium
join:2004-03-05
Centerville, IN
| reply to pmurdock
Looking for trouble here. The ports are not designed for this. They are designed to connect to 1 other device. This may work, if you can get your new device to put the ethernet port into a high-impedance state, so it looks invisible, when not operating. I doubt that it will work, though, unless the other device does the same.
Ethernet works by toggling the voltage from 0 volts to x volts between the transmit pair wires. If one device tries to drive the voltage to 0 and the other is not transmitting, the second device will do its best to maintain the x voltage. The current sourced from device 2 will go way up, E = IR, and to get to 0 volts R will be 0.
This is the reason for hubs, so every device can manage its own transmit pair.
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Scott |
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daggardale
Premium
join:2003-11-07
Gurnee, IL
 ·Vonage
| reply to pmurdock
I used a simple splitter device like this a few years back. The collision rate was terrible, but it worked. Here's a link to a cheap one, if you're interested.
»www.cablesnmor.com/index.asp?Pag···odID=698 |
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Semaphore
Premium
join:2003-11-18
Arnprior On. | reply to pmurdock
I agree with NWN & Daggar... I did say it does work..... electronically, and from a network perspective, it's terrible. It won't use any power, but it will likely induce high collisions. |
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CapinPete
Premium
join:2002-12-23
Loxahatchee, FL | reply to pmurdock
Am I missing something? Why cant you replace your access point with another access point that has a 4 port switch built in? |
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pmurdock
Paul Murdock
join:2001-09-13
Riverton, UT | Well, for one an access point with a four port switch built in will draw more power.. and second.. it is less expensive to add a four port switch than replace the whole access point am I wrong?
cheers,
Paul |
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CapinPete
Premium
join:2002-12-23
Loxahatchee, FL | I'm sure an access point with a built in switch will consume a bit more power, yes. However, it should be a lot less than an access point AND a switch. An access point with a built in switch should not cost much more than just a switch. |
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wispman
join:2004-12-21
USA | Are you talking about d link or something? |
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jdmarti1
Jack
join:2004-06-15
Oilton, OK | What kind of AP are you using???
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»magicwisp.com |
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John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp | reply to pmurdock
That reminds me...
How many watts is your panel?
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A is A |
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pmurdock
Paul Murdock
join:2001-09-13
Riverton, UT | It is an 80 watt panel.. I may just want to add another panel..
cheers,
Paul |
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John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
 ·CenturyLink
| said by pmurdock  :It is an 80 watt panel.. I may just want to add another panel.. I was going to suggest that...!
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A is A |
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John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
·CenturyLink
| Or this...
I like the wind generator. It works when Mr. Sol is hiding 'round the backside.
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A is A |
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BigCreek
God Is Good.
Premium
join:2002-06-25
Heber Springs, AR
| said by John Galt :Or this... That must be the best electrified Outhouse I've ever seen
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SBC Pro Static DSL; Linux. Terrific wife & kids; live on a farm by Big Creek. Software & network consultant. |
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