Is it possible to pair MPPT/PWM charger with Computer UPS? Would it prolong the UPS battery's lifespan?

[soe soe]

I've an old UPS for my computer which draws 50 W on average and less than 150 W at full load. With the the built-in battery I only have about 10 minutes of backup time.

I am thinking about getting a solar panel (around 150/200 W) together with a MPPT/PWM controller (around 10/20 A) so that I can charge the UPS battery (while it is running when utility power is not available). Assuming I just want to use my computer throughout the day, would the UPS be able to supply enough power to the computer as long as the sun is shining?

I also want to know if the above setup would prolong the battery's life because the MPPT/PWM charger will be constantly feeding DC power to the battery (which effectively, I assume, stops the battery discharging).

A brief background of the question: I think I should add the reason why I asked the above question. We are from a developing country in south east Asia. We get electricity only a few hours each day in winter and summer because hydroelectric power is not produced much at that time. This is a major hinderance for young people learning computer programming. Most people may not afford to get inverters along with large batteries or a few kW solar systems. So I am thinking what may be the cheapest way if we just want to use a laptop computer for a long time. Then I may be able to help others telling what can be done. Other options I am thinking include stepping up or down dc voltage of small batteries (about 40Ah or less) to match the laptop charging voltages. And I am not sure if it's appropriate to ask such a general question like "What is the cheapest way to use a laptop for a long time without utility power?".

 

[sunshine_eggo]

Answer to subject questions:

Yes.

Maybe a little. Likely won't hurt.

10 minutes is a pretty decent run time for an old UPS.

UPS chargers are typically pretty anemic requiring 24 hours or more to fully charge the batteries.

Configuration also matters. While they tend to use small SLA, many are wired in series for 24V. If that's the case, best results would be had with 2X MPPT or PWM - one to each individual 12V.

Charge and float set to 13.8V.

Panels rarely deliver rated power, and when they do, it's only in perfect conditions at high noon. If using PWM, panels will NEVER deliver more than about 80% of rated due to the way PWM work. If you intend to power directly off PV, I would go for a minimum of 300W if 150W is your consumption.

 

[efficientPV]

Depending on UPS, many aren't designed to run more than 10 minutes and might not have enough heatsink to function for long periods. Many have large blocks of aluminum to store heat with very little surface area to dissipate it.

 

[zanydroid]

Why not just get a small AIO? The inverter on the UPS is not rated to do what you want. UPSes probably have inverters with 20+ year old designs, while the AIOs should have pretty new ones that are rated for unlimited run duration.

 

[soe soe]

Thanks for all your replies!

I think I should add the reason why I asked the above question. We are from a developing country in south east Asia. We get electricity only a few hours each day in winter and summer because hydroelectric power is not produced much at that time. This is a major hinderance for young people learning computer programming. Most people may not afford to get inverters along with large batteries or a few kW solar systems. So I am thinking what may be the cheapest way if we just want to use a laptop computer for a long time. Then I may be able to help others telling what can be done. Other options I am thinking include stepping up or down dc voltage of small batteries (about 40Ah or less) to match the laptop charging voltages. And I am not sure if it's appropriate to ask such a general question like "What is the cheapest way to use a laptop for a long time without utility power?".

 

[soe soe]

I've tried and tested another possible option. I used just a 12V battery together with DC to DC boost converter (12V to 19V) and I can run my laptop playing YouTube via WiFi for 4 hours. The laptop built-in battery has been removed during the testing.

The downside of this option is that I need to do some hacking with the booster card, the cable and the jack. Wrong wiring will damage the laptop as well.

 

[soe soe]

Why not just get a small AIO? The inverter on the UPS is not rated to do what you want. UPSes probably have inverters with 20+ year old designs, while the AIOs should have pretty new ones that are rated for unlimited run duration.

Thanks, I'll check what AIOs are. I am not aware of that. Did you mean something like portable solar power station? They are available in our country. But they are a little expensive and most people can't afford them.

 

[sunshine_eggo]

AiO have high idle power draw, and their transfer switches are often too slow to be reliable as a UPS.

 

[Bud Martin]

I've tried and tested another possible option. I used just a 12V battery together with DC to DC boost converter (12V to 19V) and I can run my laptop playing YouTube via WiFi for 4 hours. The laptop built-in battery has been removed during the testing.

The downside of this option is that I need to do some hacking with the booster card, the cable and the jack. Wrong wiring will damage the laptop as well.

To me this method is the most efficient, just use proper fuses, wires, polarized connectors.
What booster are you using? It does not have adjustable output?

 

[soe soe]

To me this method is the most efficient, just use proper fuses, wires, polarized connectors.
What booster are you using? It does not have adjustable output?

Currently, I used a cheap adjustable booster, not the one properly made to be used as a laptop charger. It works well if I removed the built-in laptop battery. I think the booster has problem when the laptop do some sensing the power source to start charging. It fails the test and the laptop doesn't not allow to charge via it.

 

[Bud Martin]

Currently, I used a cheap adjustable booster, not the one properly made to be used as a laptop charger. It works well if I removed the built-in laptop battery. I think the booster has problem when the laptop do some sensing the power source to start charging. It fails the test and the laptop doesn't not allow to charge via it.

May be the booster is not rated high enough to handle the load. Do you have the link to this booster?
Did you check the power draw when running the laptop and charging the battery at the same time?

 

[zanydroid]

Laptops need 20V usually, 12V boost to 20V is no big deal.

This should be far more efficient than an AIO. You only pay the 5-10% conversion loss of a DC DC converter.

You haven’t shared math on how long you need these to run for, and what the typical power draw of a laptop is. That makes this exercise a challenge.

EG, “I need to power 30 W laptops for 8 hours off grid per day”. Then that maths out to 240Wh/boost_efficiency/(1-max depth of discharge)

And a 30W 20V converter is not difficult to find, those are embedded in USB-C chargers and power banks

I think you just need to find batteries that can charge at ~100W and discharge at 30w. 100w helps the battery recharge quickly in the morning.

 

[soe soe]

Laptops need 20V usually, 12V boost to 20V is no big deal.

You haven’t shared any math on how long you need these to run for, and what the typical power draw of a laptop is. That makes this exercise a challenge.

EG, “I need to power 30 W laptops for 8 hours off grid per day”. Then that maths out to 240Wh/boost_efficiency/(1-max depth of discharge)

I think you just need to find batteries that can charge at ~100W and discharge at 30w. 100w helps the battery recharge quickly in the morning.

I will try to provide more info for the most common case. As I have added above, I am trying to figure out the most affordable option for running laptop long hours without utility power.

 

[zanydroid]

Do you need solar for this?

I think the first part is sorting out the battery.

In the US, you can easily find kits to make 20V output, 84-100Wh USB C Power banks. With integrated charger of 60-140W.

Purchasing pre made with a reputable brand that’s USD $1-1.5/Wh. Combined with a 80Wh battery on a large laptop that is enough for quite a lot of autonomy.

Of course the DIY assembly comes with an added safety risk etc since these use Lithium cells.

 

[Bud Martin]

OP is in Myanmar (Burma) South east Asia.

 

[zanydroid]

OP is in Myanmar (Burma) South east Asia.

Yes I realize they are not from the US, but I don’t have any reference point for what things cost or are easy/hard to get, or what the typical laptop spec is in terms of W or Wh.

Absent provided specs and requirements I can only speculate from my own experience in buying stuff to give my laptop more autonomy.

 

[soe soe]

Do you need solar for this?

I think the first part is sorting out the battery.

In the US, you can easily find kits to make 20V output, 84-100Wh USB C Power banks. With integrated charger of 60-140W.

Purchasing pre made with a reputable brand that’s USD $1-1.5/Wh. Combined with a 80Wh battery on a large laptop that is enough for quite a lot of autonomy.

Of course the DIY assembly comes with an added safety risk etc since these use Lithium cells.

Agree. I better start without solar. That's why I started experimenting with DC booster. Regarding the power bank option, power banks for laptops are available here, but they are only around 20000/30000 mAh and they are not cheap. I guess we would need 2 or 3 of them to get around 6 hours running time. By the way, 70$ or less will be most affordable for most people here.

 

[soe soe]

Again, I really appreciate all your help. Yes, we are from Myanmar (Burma). Actually I teach programming via Zoom and most of my students are from various regions where electricity outages happens so badly (much worse than big cities like Mandalay, Yangon, Naypyidaw etc). Student can't even attend my classes regularly let alone doing homework and assignments. Some of them have to watch the lecture videos I uploaded on Youtube only when electricity is available. For hard working students, power outage is a major frustrating obstacle.

 

[zanydroid]

If you can find a lot of surplus or used 12V lead acid batteries sitting around, it’s hard to beat. I assume you don’t need the portability that the power banks provide.

The converter circuit of the power banks might be useful though (you can probably get them cheap on AliExpress). You can use a trigger board to request 20V from them for a non USB C laptop. If you can find one that can work with 12V. 3s of lithium is sort of close to 12V, and I think that’s a standard power bank configuration.

I don’t know if those can be configured for lead acid charging. If it can then you could just supply a decent USB C charger.

 

[zanydroid]

BTW there are dedicated battery forums with a lot of people making home power banks, etc. I think r/battery is one?

I feel what you are looking for has been figured out already by someone into that stuff for the economics etc of your country, which would be awesome and get you going soon.