relayswitches
I am trying to figure out how I can actuate a high amperage 12V relay with only the batteries I have on board.
Basically the idea is here to have a 3.7V lithium cell, a momentary switch to actuate the relay, and then let the current flow from the lithium cell through the relay to the load.
Is there any way I can do this? I'll be dealing with loads up to 60 ampere, and a lithium polymer battery that can support that kind of discharge.
This will drive a relay from a micro-controller pin: -
The relays you have described are fine and putting a contact in live and neutral is fine too. Just make sure you select your final one to switch 10A and check to see it is rated for the voltage and has a good gap coil to contacts (or is specified as being suitably safe).
The transistor in the circuit has to be able to supply the relay coil current so it may need to be rated at 200mA depending which relay you choose. Voltage rating 20V or above. If you are using a "hungry" coil and it needs more than 100mA you might want to reduce the 10k to a 2k2 to make sure the transistor turns on properly.
If the relay doesn't have an in-built diode protection circuit then you'll need to add a diode to the circuit across the relay. It's normally not conducting with the anode at the collector of the transistor. 1N400x type will do.
The relays on the shield you linked are rated for 7A at 250V AC, but I don't think the relay shield itself is designed for that.
The product page states:
Cautions:
Place 2 layers of electrical tape on the top of the Arduino's USB connector. This will prevent the relay shield from making contact. Do not operate voltage more than 35V DC.
(Emphasis mine.)
The datasheet for the relays on that board (Heli Shun HLS8L-DC5V) show that the primary coil is 5V 0.36W:
Note that the contact ratings section specifies 250V AC / 30V DC. This immediately makes me question the difference between the relay datasheet (30V DC) and the shield product page (35V DC).
Since you're using AC, this discrepancy might just be a side note. The shield product page doesn't even mention AC for the switching voltage, it just repeats the 35V DC max switching voltage.
Based on this, I don't think I would connect 240V AC, because it may be that the PCB isn't designed with the necessary voltage isolation.
Further, since you're not experienced working with mains voltage, which can be extremely dangerous, I don't recommend doing so without the assistance of a professional.
Best Answer
This can boost 3.7 to 12V, about 1 to 2A. Enough to drive sizable relay.
Not sure if relay is needed. Can simpler mechanical switch do?
http://www.coolcomponents.co.uk/adjustable-4-12v-step-up-voltage-regulator-u3v50alv.html#.