Need help with a project involving solar cells and SLAs - Page 3

poobah · 26th July 2006, 08:41 PM

Actually, the Vmax spec. on the T-Amp is questionable... double check it. It is a class D amp so I don't think some variation on the power supply should hurt much, but spec's are spec's and you must follow them...

Now, you are solar charging the batteries... so 14.0 - 14.1 is a better value then 13.8.

So the problem is how to get down from the 14.0 at the battery to the 13.2 (max) of the T-Amp... you could use another shunt regulator, you could use a "LOW Dropout, 3 terminal, 12 Volt regulator". OR, you could use two regular diodes in series for a drop of 1.2-1.4 Volts... very simple.

Mcuh depends on how you plan to do your AC charging. Any decisions there?

Saturnus · 26th July 2006, 09:09 PM

Quote:

Originally posted by poobah
Much depends on how you plan to do your AC charging. Any decisions there?

I'm leaning towards this

http://www.ham-kits.com/SLACharger1.htm

schematics here

http://www.ham-kits.com/SLACharger/SLA%20Charger.pdf

I'll need to modify it for 240V AC, though but that's pretty simple.

Saturnus · 26th July 2006, 11:54 PM

I couldn't just let it rest, could I?

A quick search in the local parts shop junk pile revealed some BD536 (datasheet below).

It's TO-220 package, has relatively low Hfe (min 40), and is relatively low frequency.

If I dropped that into your circuit using the components which I desribed above (not correct voltage, I know, but I can ix that later) then R(base) would have to be 1K1ohm but I assume I could use a 1Kohm. Correct?

If so, then I'll have a look at the other numbers tomorrow to increase the voltage slightly. And still assuming it's correct, I don't see any reason why I couldn't and shouldn't use an identical circuit for dropping the voltage from the battery to the load. With different values naturally.

Datasheet: http://www.ortodoxism.ro/datasheets/...onics/4133.pdf

poobah · 27th July 2006, 12:10 AM

You want to sink (shunt) 1 amp solar max. Divided by Beta min equals 0.025 amps. You have 10V max or so across the base resistor to accomplish that... So that gives you 400 ohms max for Rbase.

Perhaps a "PNP darlington" would be a better choice because of it's higher beta. The TL431 should not have such a high current.

Now, a shunt regulator is handy for a solar panel because a solar panel is really a current source... not a voltage source. Your battery on the other hand is definitely a voltage source. Research the low dropout 3 terminal regulator.

oh...get some sleep!

poobah · 27th July 2006, 05:06 AM

Something else to think about here... a shunt only diverts current when an excess of voltage commands it to do so. In the case of the solar panel, it will only divert current when the battery reaches 14 Volts... in other words charged... doesn't need the current.

Now what happens if you use another shunt to regulate the battery voltage down for the T-Amp???

Hint: keep in mind you do have to put a resistor between the battery and the shunt to do this.

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26th July 2006, 08:41 PM	#21
poobah diyAudio Member Join Date: Nov 2005	Actually, the Vmax spec. on the T-Amp is questionable... double check it. It is a class D amp so I don't think some variation on the power supply should hurt much, but spec's are spec's and you must follow them... Now, you are solar charging the batteries... so 14.0 - 14.1 is a better value then 13.8. So the problem is how to get down from the 14.0 at the battery to the 13.2 (max) of the T-Amp... you could use another shunt regulator, you could use a "LOW Dropout, 3 terminal, 12 Volt regulator". OR, you could use two regular diodes in series for a drop of 1.2-1.4 Volts... very simple. Mcuh depends on how you plan to do your AC charging. Any decisions there?

26th July 2006, 11:54 PM	#23
Saturnus diyAudio Member Join Date: Jun 2005 Location: Copenhagen, Denmark	I couldn't just let it rest, could I? A quick search in the local parts shop junk pile revealed some BD536 (datasheet below). It's TO-220 package, has relatively low Hfe (min 40), and is relatively low frequency. If I dropped that into your circuit using the components which I desribed above (not correct voltage, I know, but I can ix that later) then R(base) would have to be 1K1ohm but I assume I could use a 1Kohm. Correct? If so, then I'll have a look at the other numbers tomorrow to increase the voltage slightly. And still assuming it's correct, I don't see any reason why I couldn't and shouldn't use an identical circuit for dropping the voltage from the battery to the load. With different values naturally. Datasheet: http://www.ortodoxism.ro/datasheets/...onics/4133.pdf

27th July 2006, 12:10 AM	#24
poobah diyAudio Member Join Date: Nov 2005	You want to sink (shunt) 1 amp solar max. Divided by Beta min equals 0.025 amps. You have 10V max or so across the base resistor to accomplish that... So that gives you 400 ohms max for Rbase. Perhaps a "PNP darlington" would be a better choice because of it's higher beta. The TL431 should not have such a high current. Now, a shunt regulator is handy for a solar panel because a solar panel is really a current source... not a voltage source. Your battery on the other hand is definitely a voltage source. Research the low dropout 3 terminal regulator. oh...get some sleep!

27th July 2006, 05:06 AM	#25
poobah diyAudio Member Join Date: Nov 2005	Something else to think about here... a shunt only diverts current when an excess of voltage commands it to do so. In the case of the solar panel, it will only divert current when the battery reaches 14 Volts... in other words charged... doesn't need the current. Now what happens if you use another shunt to regulate the battery voltage down for the T-Amp??? Hint: keep in mind you do have to put a resistor between the battery and the shunt to do this.

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