In a message dated 04/07/05 19:56:32 GMT Daylight Time, [EMAIL PROTECTED] writes:
There are some small charge controllers out there, but a relay configured to open when the battery reaches full charge is the simplest. Reply:------------------------------------------------------------------ The problem with using a relay for solar charge control is the current needed to activate the coil of the relay. This could be as high as 100mA and with a charge budget available of only 250mA you would have to select the relay used with care. If a solar charge controller was seen to be necessary I would have thought a solid state version similar to the type Don Brown is making the kit for would have been a safer bet for minimising power losses in the control mechanism (pity these are only available in the USA as I could have used one). The usable solar power available for solar panels is usually calculated at 8hrs per day, though does depend on the seasons further away from the equator. With 8hrs @ 250mA that would equate to 2000mA per day which is the total rating of the NiMH cells being used. The charge needed would depend on the initial state of the batteries and what the consumption of the radio was to offset the available charge. Some device to monitor the battery voltage and an on/off switch would also work as a charge controller in this case at probably even less cost. With regard to the point when full charge is reached with NiMH cells, I was checking out a motorcycle racing ignition pack last week and using a commercial charger built for the purpose, the end voltage for a 6 NiMH pack was 8.40V, which equates to 1.40V per cell. These guys can get exceedingly upset if they are leading a race and the batteries die, so had to ensure that all was OK. The point with this type of cell and many others including gel cells is that the initial voltage at the end of charge is higher than the nominal voltage of individual cells, though the voltage soon droops with use to the nominal voltage of approx 1.20 to 1.25V per cell. This carries on pretty well constant until the battery is almost empty then there is a rapid fall as the battery dies. Under these circumstances using NiMH cells it would be better to maintain the charge to prevent the voltage falling as was recommended. Understand with the earlier NiCADS it was better to take them as far as possible before recharging otherwise cell capacity could reduce. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
