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There were no significant updates to our portable dvb-s receiver project, due to war. Situation now calmed a bit, so I performed a series of tests.
I’ve measured voltages and power consumption of various power lines of SR55X receiver. The results are:
22V Line: Idle current – 40ma. LNB and DISEQC/Motor power will be taken from here, so actual consumption may be 550mah. Voltage under no load is 24V, under load (Diseqc+LNB) it drops to 23V.
12V Line: Idle current – 16ma. The power for 0/12V switch is taken from here, so maximum current will be 50+16=66ma. Actual voltage was 14V
5V Line: Idle current – 100ma. In working mode – 130ma. Voltage 5.4V
3.3V Line: Idle current – 170ma. In working mode – 480ma. Voltage 3.4V

So what conclusions can be done?

As power consumption is much lower than expected, lower cost and easier to find IC can be used for achieving desired voltages. Example circuitry will look like this:

Separate MC34063A used for 3.3V, 5V, 12V provision. For 22V, MC34063A also can be used, but current will be limited to 350ma in this case, which may cause diseqc/motor operation unstable. So we have to use some more powerful IC here. If your main power supply will be 12V DC, than you’ll need LM2577, If supply is 24V, than you’ll need LM2576. These ICs are quite simple and robust in operation.

This program will be useful for begginers and sat dx-ers. How many times, you’ve pointed dish somewhere, set receiver to blind scan, found some frequencies, but have no idea which satellite is that? Now this program will help you. Just type in received transponders frequency, and it will tell you satellite name and orbital position. You can increase precision by typing in polarisation and symbol rate.

Download english version

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Regarding our project, there are several ways to power our discoteque from batteries, below I’ll try to list them, according to manufacturing difficulties.

1. Most cheap, least economic, most easy way. Is to use external 12V sealed lead-acid battery, and use generic 12<>220V invertor, to power existing PSU of DVB-S. This is most easy to do method, but has much less efficiency, and quite large weight, to overcome it’s limitations we can:

2. Built a custom power supply, which works from 12V. Output generally should be +3.3, 5, 12, 22V. This is a bit tough task, since generic available designs have almost same productivity as idea #1. If using DC12V from SLA, achieving good performance won’t be so hard, especially if we’ll take say 2pcs 12V 2Ah batteries connect them to get 24V, instead of 12V 4Ah one.

3. If you really good in electronics, you can built a custom PSU, which will be driven from LiIon battery. This requires better skills, since LiIon is very sensitive to overload, overdischarge and temperature changes, but will give much more better weight/performance. To give you idea of battery performance of various type, below you can find a quick comparison of various types:

capacity and weight (assuming voltage is 12V)

NiCd – 300 grams  0.9-1.3Ah

NiMh – 300 grams, 1.3-2.2Ah

LiIon – 150 grams, 2.2-2.5Ah

Pb -  1000 grams, 2-2.4Ah

As you can see, LiIon seems to be best choice, but, it has other concerns:

1. You can’t draw as much current from it, as you can do in case of Pb or NiCd.

2. It needs much more attention during handling.

3. You should monitor discharge current, minimum voltage, temperature.

4. You can’t safely charge it by dirt cheap charger overnight.

Considering all above, LiIon may seem to be totally unusable for our tasks, but we can be a bit smart, and use some “gifts” from industry, such as… Video Camera batteries! Usage of them has several advantages in front of bare LiIon cells:

1. Camera batteries always have discharge/overload shutoff/protection circuitry.

2. A lot of them have built-in charge level indicator

3. Chargers are available in wide range of design and features.

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