Grid Powered Charger

A couple of questions for you. First if ones battery voltage drops below our set threshold then the unit will allow a charger to charge the batteries from grid supply but because most chargers are not capable of supplying the current needed to run ones inverter then the house itself is now without power? Do you suppose then that the relay that connects grid power to ones battery bank be used to switch the house breakers from grid to inverter? Finally could not this whole operation be done with a single relay where in the coil in energized from the inverter? Most inverters have a low voltage shutdown so when the inverter senses a low DC voltage it shuts down and power that was normally routed from our inverter to our house breaker via the NO contact would switch to the NC position connected to grid voltage. If one desired they could then charge the battery bank from the grid source. Looking forward to your reply Regards Jason

Jason, you pose some interesting thoughts. If you use a small charger, you would need to be careful about your load. In my setup, my Iota charger is capable of running my load and charging the batteries. The load consists of refrigerator, blowers and ignition for two gas heaters, the same for a gas water heater, and two lights in my living room.

The objective of the grid switch is to top off the batteries as they become low and there is insufficient current from wind or solar to charge them. Your proposal of using the relay to switch from inverter power to grid power would work, however you would need more than a SPST relay and that could affect cost. If you were to try to simplify the circuit down to a single relay triggered by the inverter's under voltage threshold, I think you would run into troubles because there is nothing to switch the relay back to inverter power after it has switched to grid. The inverters I've seen (admittedly, I've only seen the inexpensive ones) require the user to press a reset switch to get them running again once the under voltage shutdown occurred. In the context of your proposal, the grid switch accomplishes three things. It makes the inverter's under voltage cut-off completely automatic; it switches the power source rather than shut it down, and it gives you some flexibility as to the threshold voltage rather than force you to live with 10 volts, which I think might be rather low. Thanks for your comments. --Tom

After thinking about Jason's question some more, I want to give my thoughts about choosing the right size battery charger to work with the grid backup switch. Please understand that you will only be able to continuously draw whatever the stated capacity of the charger is. You do have ability to handle larger intermittent peak loads because the batteries can give the extra juice when you need it. A small charger will take longer to charge your batteries.

Perhaps a rule of thumb to use when deciding on the right equipment is to choose a charger with a capacity as close to the maximum output of your solar or wind generating equipment as your pocketbook will allow. This will insure rapid charging and the ability to maintain the normal loads you place on your inverter. --Tom

do you have a 240v version of this kit? in new zealand and australia the grid is 240 volt.

Hi Cameron, It does not matter what the voltage of your local grid may be. The grid charger voltage switch will run ok. All you need is a solid state relay that is capable of operating at your local grid voltage. Since the switch uses a TTL level signal to operate the solid state relay, make sure that whatever relay you choose has a dc control voltage of 3-5 volts. Many relays have a 3-32 vdc range and thse are just fine for the grid charger voltage switch.

Is there a set-up for 48 volt systems. I'm using 8 Rolls 6V batterys on my system here in Bayfield, Colorado. Thanks for any help. Also not grid tied only generator back-up! Larry Frey

Larry, there is no 48v system available at this time. If you send me an email with some information about your system, I might be able to make some modifications to the switch so it would work for you. Do you use an inverter? What voltage feeds it? What is your generator's charge voltage? What kind of charge controller do you use? --tom

are there any issues with connecting this in conjunction with the a solar charger? for example a trace C40 is tied to solar panels and does the charging of a bank of batteries If I read the description correctly using the kit would then hook up a second charger to the same battery bank. So the potential exhists that there could be 2 chargers charging the bank at the same time? --chris

Chris, Your understanding is correct. The grid charger switch is designed to control a second grid powered charger that runs in conjunction with a solar charge controller such as your C40. It's ok to run two chargers on the battery bank at the same time. Each charger sees the other as if it were the battery bank itself. Thus the chargers reduce their charging current somewhat until the batteries are fully charged. The grid charger switch will turn on for a preset amount of time and then turn off The charger that is connected to it will handle the control of the charge current.

In practice, the grid charger switch will only turn on when the batteries become low due to a constant load, but no sun due to poor weather. If you use a large enough charger to handle your load (the Iota 55 amp charger I use has been terrific for me), it will make your system brown-out proof. Your batteries will never go low even during extended periods of cloudy weather, you will be able to keep your normal loads connected, and your solar panels will provide power when the sun is available. It's really the best of all worlds. --tom

Hi. I’m interested in buying the battery charger part of your device. The one on your site that cost $12 bucks, is that the charger? The one that comes in the metal box? I want to try to build the circuit on my own but I just don't know if I can build the battery charger, so I just want it ready so all I have to do is tie them together. Please let me know, and also I want to get the preprogrammed PIC. Another question, How do I do the paypal invoice?

Hi. Just to make it clear, this is not a charger. It is a switch to turn a charger off and on automatically. The bare printed circuit board is what costs $12. You can buy the board with components, including the preprogrammed PIC chip (you assemble it!) for $30. Or you can buy the unit assembled and tested for $60. To the completed unit you would need to also supply a battery charger, an enclosure, a properly sized solid state relay, and connecting wires. To use paypal, you need to set up a paypal account. You will receive info on setting up an account if you ask me to send you a paypal invoice. If you choose not to use paypal, that's ok. You can just do it the old fashoned way and mail me a check. Thanks, Tom

Can you please Post your contact information like a phone number where we can call you.

I hope you won't mind, but I'd prefer that contacts be kept to emails. I sell stuff, but it's not really a business. It's more of a hobby. And I'm out at work all day anyway. Thanks, Tom