Making a 1A 9V UPS

[Blapto]

The situation:
I get fairly frequent 5 second - 3 minute powercuts.
I use a laptop and an old laptop for my wireless router, so that stays up.
My ADSL modem/router doesn't.
The ADSL modem wall wart supplies 9V 1A.
Basically, I would like to put a 9V NiCd cell in there, with about a 150mAh capacity, which I suppose is good for 9V up to 100mAh and therefore will last me for 6 minutes.

Anybody got any input?

Thanks.
Martin Lee.

 

[andrew2022]

ull want more battery power than that. the capacity is based on a 24 hour discharge rate so itll last less than u predict. also, where did u get the 100mA from 1A (1A is 1000mA

 

[k7elp60]

Making a 1A 9V ups with Nicads may be a little hard for the following reasons:
Nicads are rated at 1.2 volts per cell, need to be charged when they reach the cutoff of 1.0 volts and they require approximately 1.5 volts to fully charge. So with 7 cells the cutoff is 7.0 the battery would be 8.4 and it would require 10.5 volts to charge the pack. With 8 cells the cutoff would be 8.0, the battery would be 9.6 volts and would require about 12 volts to charge.
A possible better solution would be a 12V lead-acid (gel-cell) and charger and a 9 volt regulator. This would supply 9V for the router and would work fine.

 

[fat-tony]

A possible better solution would be a 12V lead-acid (gel-cell) and charger and a 9 volt regulator. This would supply 9V for the router and would work fine.

And I suspect it would last a really long time.

 

[Sebi]

I also recommend a lead-acid maintenance-free accu. The 7Ah type is cheap, and designed for 13.8V continous charge mode.
In the regulator position work fine the LM2657 (1A) buck regulator with 90% efficiency.

 

[Blapto]

The UPS must supply 1A, but the battery is a 9V nicad (designed to replace the cuboid 9V batteries in fire alarms and such) that has a capacity of 150mAh.

How much am I looking at paying for a 12V gel cell in the UK?

**broken link removed**

ah-hah.

So £15 or so, reasonable.

I just can't get my head around both charging the battery and powering the router at the same time. The router draws up to 1A, yet the maximum charge rate of the lead acid will be 1.5A or so.

 

[gerty]

just can't get my head around both charging the battery and powering the router at the same time. The router draws up to 1A, yet the maximum charge rate of the lead acid will be 1.5A or so

As long as the circuit draw does not exceed the charge rate your device will run fine and your battery will charge..

 

[panic mode]

why not buy small UPS for PC and simply plug the DSL wallwart into it?
When loaded with a PC and monitor (ca 300-400 watts) even small and
cheap UPS would run for 3-5minutes. If you use it to power only small
wallwart (ca. 15Watt) it should last at least an hour.

 

[Sebi]

O.K.,just be sure, the wallwart supply not contain transformer for 50(60)Hz, because most of UPS designed only for SMPS.(the output voltage not sinus, so the rectifier output give much higher DC)

 

[Blapto]

Even a cheap UPS is £50.

I want my homemade one to output 9V DC @ 1A max.
From what I have read here it seems I should I need a 14V charger, a lead acid battery, a buck regulator and just connect everything in series?
= <-- + and - wires
charger==battery==regulator==modem

 

[evandude]

no, charger goes in parallel with the battery. then the inputs of the regulator are connected across the battery terminals, with the output goes to your modem.

 

[Blapto]

I'm just a little worried about charge rates. The modem draws up to 1A, probably typically 700mA. Why would the transformer have extra current drawn to top the battery up? Or wouldn't it, and I would just top up the battery manually every month or so?