DIY UPS low voltage question

bonald

10 mW
Joined
Jul 4, 2012
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25
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Canada
So I made this DIY UPS with a 1500w inverter, 4s Winston battery, 15v meanwell PSU and a amp meter configured with a LVC set to 11.5v.
Everything works fine except that there is no recovery voltage on the amp meter, when it hits LVC it won't come back ON unless I press the power button.
I can't use a BMS at the cell level because the battery is sealed.
Does anyone knows a device that I could set a LVC and a Recovery voltage? (Shutdown at 11.5v PowerOn at 13v)

1cROJ1v.jpg
 
A simple op-amp or comparator with some built in hysteresis and a voltage reference should do the trick. Connect the battery voltage to your positive input through a voltage divider and the negative to a known, stable voltage reference. Comparator goes high above your set point and low below it. Swap the inputs to invert the signal. This assumes you can somehow turn the meter back on other than hitting the button.
 
I found what I was looking for:
http://www.reuk.co.uk/buy-MINI-12V-PROGRAMMABLE-LOW-VOLTAGE-DISCONNECT-LVD.htm

Now my UPS is complete.
 
so that battery has no way to balance itself inside the plastic case? you could cut the top off and add some sense wires to it. if you did that then you could add a balancing network to keep the battery balanced.
 
dnmun said:
so that battery has no way to balance itself inside the plastic case? you could cut the top off and add some sense wires to it. if you did that then you could add a balancing network to keep the battery balanced.
I second that recommendation, especially after reading this from a website selling them (http://www.ev-power.eu/LiFeYPO4-batteries-12V-1-1/Lithium-Battery-12V-40Ah-WB-LP12V40AH.html). Seems pretty sketchy to me, regardless of the quality of the cells inside they're not going to be identical. (The misspelling on the word "performance" is their mistake, not mine...)

NOTE:
The monolithic 12V batteries do not have any PCM (any electronics) inside. They consist of finely balanced cells with identical perfomace. The battery must be managed as a single monolithic 12V block.
 
i wonder if the chinese computers these guys use have the same spell check that comes with english language browsers here.

but that battery is not sealed, as in sealed lead acid battery. it is just glued on top and that can be cut around the perimeter on the glue line with a table saw to expose the pack inside.

i have never seen a lifepo4 pack that was able to maintain balanced cells.

this is an old problem, and always warning people about them but they still keep selling them. this is how lithium gets a bad reputation when they die so quickly.
 
dnmun said:
i have never seen a lifepo4 pack that was able to maintain balanced cells.

But it's LiFeYPO4 ! What?
For scientific purpose, I'll update this thread in 6 months with the cover removed and I'll take mesurement on each cell.

I have 5 more sites that will need a UPS like that, anyone have a better battery to recommend?
 
Any one knows what are the balance board connected to his cells?http://youtu.be/oJ8AfJsOhsM

Edit: that's minibms board.
 
bonald said:
I have 5 more sites that will need a UPS like that, anyone have a better battery to recommend?
Sealed lead acid would be my choice, despite how much of a fan of lithium I am. It's cheap and proven for this application. Perhaps someone else will chime in here, but it's not ideal to leave lithium batteries at 100% SOC constantly, keeping them in the 30-80% range is ideal.
 
We are trying to move away from SLA. We keep changing them every 2-3 years because they lost most of their capacity.
We also tried deep cycle marine battery but we had to refill them with water constantly and they still failed after 3 years.
 
bonald said:
We are trying to move away from SLA. We keep changing them every 2-3 years because they lost most of their capacity.
We also tried deep cycle marine battery but we had to refill them with water constantly and they still failed after 3 years.
If absolute minimal maintenance is paramount and you have a big enough budget and you don't need a lot of down time of mains power supply (although really limited on budget) you could use ultra-capacitor setup.

This one below holds maximum 16volts, you could build up a larger Ah total by putting more in parallel.
http://www.ebay.com/itm/6-Maxwell-650F-2-7V-Ultra-Capacitors-w-Balancing-Circuits-/221544481658?pt=LH_DefaultDomain_0&hash=item339514837a
With over 500,000 cycles each with a perfectly controlled environment your setup could last up to a million years without the need for battery maintenance.

I have seen various setups on youtube can't find my preferred one but this guy has an emergency Ultracap+inverter to a blender for emergency smoothies I guess.

[youtube]UkXKJSwe2ag[/youtube]
 
do you have to build this setup for each of the UPS locations? the device you linked to is what dmw was talking about the 8 pin IC with the 322 on it is a dual op amp that does like he said you would wanna do.

the standby drain current is gonna be the circuit current needed to keep that hysteresis board powered up and the circuit current for the AC detector that initiates the switch on of the light. the detector board may take a lot of current, depending on how they wire up the voltage dividers for the op amp inputs.

if you can charge to a lower voltage than 3.6V that would extend life cycles imo also. it will be interesting to see how well balanced the pack is later and it may not be a significant issue either.

but that is a very complicated setup but maybe it will get simplified to just a small charger and the UPS controls. if you leave a charger or power supply connected you should open the power supply and cut out the resistor across the output capacitors to reduce the drain down current that would leak out of the battery back into the charger and into that drain down resistor.
 
dnmun said:
do you have to build this setup for each of the UPS locations?

Yes

dnmun said:
if you leave a charger or power supply connected you should open the power supply and cut out the resistor across the output capacitors to reduce the drain down current that would leak out of the battery back into the charger and into that drain down resistor.

If I understand correctly, If I don't cut that resistor and main AC goes out, the charger will drain the battery because of that resistor?
Where would that resistor be on this particular power supply?
KkLexpU.jpg
 
dnmun said:
the device you linked to is what dmw was talking about the 8 pin IC with the 322 on it is a dual op amp that does like he said you would wanna do.
It's actually a microcontroller, I suspect the 322 is part of a lot code or date code. Regardless, it's probably programmed to perform the same function as an op amp, and hopefully also goes to sleep periodically to save power.
 
man, just assumed it was a dual op amp like the 324 since it was 8 pins.

it does look like that device will consume some current too, looked like there was two sets of resistor dividers which will eat current too.
 
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