Homebrew online double conversion help please

[lazyjss]

My plan is to homebrew a online double conversion ups for my computers as my electric grid here is spoty, located in eastern usa.

A quality sine wave inverter and a battery bank is easy enough, my question comes from what to power the battery bank with as it will be also responsible for charging batteries after an outage, will be using 120vac mains power for input and from what i can find a telecom rectifier is recommended for continuous dc voltage.
Would someone be kind enough to point me in the direction of a continuous power supply for the inverter with possible battery bank charging capability.

Thank you for any advice

 

[Ampster]

Without knowing the size of your project it is difficult to make a recommendation. Many off grid inverters include a battery charger and the benefit is that controls are integrated. Is there a reason you are not considering that approach. I am not sure what you mean by double conversion?
powering your computers with a hybrid inverter programmed to charge the batteries would avoid any lag time when power went out.

 

[John Frum]

I used an iota converter
samlex pst inverter
280ah@24 volt LFP battery
and a raspi to control the converter

 

[lazyjss]

Without knowing the size of your project it is difficult to make a recommendation. Many off grid inverters include a battery charger and the benefit is that controls are integrated. Is there a reason you are not considering that approach. I am not sure what you mean by double conversion?
powering your computers with a hybrid inverter programmed to charge the batteries would avoid any lag time when power went out.

Average 200 watts with peak being maybe 500watts at 120vac, I am trying to avoid any switching delay and want the extra isolation from voltage dips and peaks ruining my pc gear, so would like to run the gear off a sine wave inverter 24/7.

Double conversion and or Online is what the UPS companies are calling it when the inverter powers the gear all the time instead of a transfer switch from mains to inverter when power goes out.

My confusion comes from i am unclear how to power the inverter with dc voltage and sufficient amperage to cover the inverters power draw as it will be used non stop and only powered from battery bank when mains and the dc charger go out.

 

[lazyjss]

I used an iota converter
samlex pst inverter
280ah@24 volt LFP battery
and a raspi to control the converter

 

[lazyjss]

the iota converter will be ok to power a inverter non stop, as well as keep the battery bank topped off as long as appropriately sized?

may i ask what the raspi is monitoring and what kind of commands?

 

[Leeds]

What exactly are you powering? Most computers like to be fed DC anyway, why not tailor your system to feed them DC directly? Then the only "backup" part is how you charge the battery bank. Solar when possible, grid fed below a certain voltage, etc.

 

[lazyjss]

What exactly are you powering? Most computers like to be fed DC anyway, why not tailor your system to feed them DC directly? Then the only "backup" part is how you charge the battery bank. Solar when possible, grid fed below a certain voltage, etc.

powering a desktop pc that also serves as a nas, goal is constant and reliable power as i have already had equipment damaged from poor power grid.

power would come from mains to feed a dc charger that will power a sine wave inverter and keep a battery bank topped off and in a mains power lost event inverter would continue to run without need for a transfer switch.

i am unsure of what to use for a dc power supply that will power said inverter and keep battery bank from discharging and or overheating when charge recovery from power loss once mains come back on.

 

[time2roll]

I like the Meanwell NPB series chargers. Available in various voltage and current to fit the situation.

 

[Leeds]

You're powering a desktop PC?

They require 12vdc power and 5vdc power. A 12v bank and a DC to DC 5v regulator would power a desktop perfectly. No need for an inverter just to pump power into your computer's rectifier.

Unless you're also running a monitor this seems like a slam dunk...

Edited - The device you need is a "DC ATX power supply." It will accept 12vdc and it'll replace the AC->DC converting one you're currently using

 

[John Frum]

the iota converter will be ok to power a inverter non stop, as well as keep the battery bank topped off as long as appropriately sized?

Yes

may i ask what the raspi is monitoring and what kind of commands?

The iota talks to the bms using @melkier 's jbdtool
it uses a solid state relay to control the boost/float state of the converter.
It also uses an ac relay to power the converter on and off.
From 7 pm to midnight the converter is in float mode.
From midnight to ~6 am the converter is in boost mode.
From 7 am to 7 pm the converter is powered off.

 

[Ampster]

My confusion comes from i am unclear how to power the inverter with dc voltage and sufficient amperage to cover the inverters power draw as it will be used non stop and only powered from battery bank when mains and the dc charger go out.

I think @smoothJoey may have alluded to that. With LFP batteries you do not want to maintain them at a high voltage so the concept would be to power the inverter with a DC power supply also connected to the batteries, That way the inverter is always on and there is no delay when the power supply drops out when power goes out. The key will be to find a voltage right around resting voltage of LFP to set the power supply.

 

[John Frum]

My confusion comes from i am unclear how to power the inverter with dc voltage and sufficient amperage to cover the inverters power draw as it will be used non stop and only powered from battery bank when mains and the dc charger go out.

LFP batteries like to be cycled.
In my case I have a raspi power off the converter from 7am to 7pm which is peak rates in my local.
The converter voltage is 26.7 volts from 7pm until midnight.
From midnight until the battery is fully charged(~6am) the converter voltage is 27.7 volts.
When the battery is charged the converter drops back to float voltage until it powers off at 7am.

 

[time2roll]

Simple wall timer could cycle a charger.

 

[lazyjss]

I think @smoothJoey may have alluded to that. With LFP batteries you do not want to maintain them at a high voltage so the concept would be to power the inverter with a DC power supply also connected to the batteries, That way the inverter is always on and there is no delay when the power supply drops out when power goes out. The key will be to find a voltage right around resting voltage of LFP to set the power supply.

I would be ok with using lead acid batteries and if so seems that as long as the dc charger voltage was set correctly i would not need a bms?

 

[73powerstroke]

You're powering a desktop PC?

They require 12vdc power and 5vdc power. A 12v bank and a DC to DC 5v regulator would power a desktop perfectly. No need for an inverter just to pump power into your computer's rectifier.

Unless you're also running a monitor this seems like a slam dunk...

Edited - The device you need is a "DC ATX power supply." It will accept 12vdc and it'll replace the AC->DC converting one you're currently using

Those are pretty cool. Had a pc on one before. 12v

 

[curiouscarbon]

random brainstorming:

•PSW inverter
•LFP battery
•meanwell 12V power supply
•solid state relay between 12V power supply and input power wall plug
•microcontroller or raspi to control relay

•with meanwell 12V power supply disconnected from battery but connected to wall, turn the potentiometer and check voltage with multimeter until it is between 14.0 and 14.4 volts or so.
•connect LFP battery to PSW inverter
•connect meanwell power supply to battery
•configure arduino or raspi to connect and disconnect the meanwell power supply ("converter") on conditions you like

sensing the voltage of the battery can be one way, or a simple timer can work too. happy to help with arduino code if this is interesting.

one potential issue that could arise is if the battery voltage gets too low, the power supply/converter could charge the battery too fast and degrade its lifetime.

hope this helps in some way, cool project, good luck!

 

[krby]

@John Frum : Apologies for the necro-post. I'm trying to figure out if I need the RPi controller.
My current situation:
I've got a small network rack in the garage running off a consumer UPS. With the NAS on, it's about 100-200W. Everything needed to keep the house online is here (modem, router, PoE switch, wifi APs plugged getting power from PoE switch). When the power goes out here, the UPS tells the NAS to shut down and then will run everything for about 30-40min. With the NAS off, it's about 50W of load. When the mains power goes out, I go hook up an inverter up to my car (an EV which is parked right in front of the network rack) and then I move the AC input to UPS from the mains to inverter. This let's me treat my EV battery as a power source. I've tested this and I know it works and I understand how to keep the car "on" enough to run the 12V system from the main traction battery. A 50W load is no big deal for this.


What I would like:
I'm going to sell the EV, but I'll miss the 'keep the network up" capability. I've got a sort of mobile battery backup solution for other things in the house, but it's annoying to have to run cords all the way out to the network rack. What I want to do is a cheap DIY UPS. Given I only have about 50W of load (I shut the NAS off when the mains power is off) I was thinking I could get by with SLA deep cycle batteries. If I do that, do I need the controller you mentioned or can I essentially keep them at float charge all the time? If so then the equipment is just:
- Converter keeps batteries charged
- sine wave inverter runs the load full time
- Somewhere around 2400wH of usable capacity in batteries (50W * 48hrs). Assuming I can discharge 12V deep cycle batteries down to them 70% that's about 3400Wh, so 280Ah of 12V batteries.

Do I have this right? I guess I'd replace my existing consumer UPS with this.