one for the solarists

[Anguz]

bit of background.
i have a standalone solar setup, 800 watts of panels charging gel batteries through a victron mppt
its feeding and invertor, supplying about 120 watts to 2 switch mode power supply's on a cctv system
not got as far as running in anger yet, as i feel that there wont be enough storage available overnight or winter.
mains is available, but i have not built my voltage sensing circuit yet to stop the batteries being discharged too far

as i see it i have 2/3 options....
1, i could put a 12volt power supply across the batteries, and turn that on as an when the volts in the system drop below my low setpoint

2, or i could use something like this and hope the switchmodes stand it ...this
or i could build something similar with a changeover relay/contactor, not sure if these switch fast enough? the out of sync mains shouldn't matter to a sm power supply as its all rectified anyway ?

 

[voipio]

What is the storage capacity of the gel batteries?

800 Watts peak will be able to deliver around 700kWh over the course of the year, at your latitude. How much of this potentially available energy is actually used depends on weather conditions, season, battery storage capacity, and system power consumption. Expect to get as little as 24W from the panels during a cloudy winter day.

The simplest solution would be to have a user adjustable mains to DC power supply permanently powered from the mains, with the output connected to the batteries, and the output set to a suitable voltage. Modern switched mode power supplies tend to consume very little power when the output is above the set point. The value of set point to choose will depend on how much battery reserve is needed when solar panel output is low and the mains fails. The condition of the battery, and the current being drawn as a fraction of its capacity, will influence this decision e.g. using a set point of 12V on a 100Ah battery, where 120W is being drawn by the CCTV system (i.e. C/10), will give 50% remaining capacity if the mains fails, and will stop the battery discharging below 50% under normal conditions, thus maximising battery life. For some pointers, look at some discharge curves e.g: https://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

 

[Gareth J]

If mains is available, have you ruled out grid tying and using a little hybrid inverter?

 

[finyuk2005]

you cant use a boost converter to supply the cameras instead of the inverter and power supplies could you?
It would be a more efficient system i would think
Also, if you had a 12v power supply set just above the lowest safe voltage for the battery, it would only really be delivering power when there is no sun and the batteries are getting low
i think anyway!

 

[knighty]

what voltage are the batteries? if 12v just feed the cctv stuff directly?

for mains charging, just get a little charger, or an adjustable power supply (lots have a little potentiometer on to adjust voltage) set it to 13.5v and forget about it

I'm assuming solar is just for backup? if you want to use mostly solar... (might as well?) set the psu to 12v... that way it won't do anything till voltage drops under 12v

 

[Anguz]

12v batteries.. the cameras are poe so running at 50v. i could ditch one of the internal supplies and run the recorder direct of 12v,

 

[knighty]

poe switch running them? you could get a dc to dc converter instead

so recorder direct on 12v, dc to dc supplying the network switch the cameras are plugged into

should be more efficient than running the inverter and power supplies for both


or... you could just have a power supply set to 12v joined to the batteries... that would stop them running flat any time... you're probably not losing that much in the inverter and power supplies

check and see how hot the inverters and power supplies are getting.... how hot they are will be how much power they're wasting / how inefficient they are

 

[Anguz]

They are quite efficient barely warm

The poe switch is part of the recorder

 

[knighty]

honestly then... probably not with messing with... and probably a pretty robust system

get a 12v meanwell (it's a good brand) power supply, dial it in to 12 (or just over) leave that plugged into the mains

if the solar ever can't keep up with the battery charging that will stop them being run flat

next day when the sun shines again the solar can top the batteries to full charge

how big are your 12v batteries? 120watts is about 10 amps, so even in a power cut and no solar there should be enough charge to keep the cctv going a decent time