Solar-Low voltage protection

[David95436]

I have a new All Terrain Bobcat with the standard solar package. Today, I got a Whistler PI-1200W inverter, wired directly to the battery. To preserve battery life, I don't want the battery to discharge more than about 50%. If my inverter does not warn me, is there anything else in the system what will prevent excessive discharge? Would I have to get a better inverter or a low-voltage discharge meter?

Thanks

David

 

[bobg333]

You need a Charge Controller. I have a Morningstar which I like a lot but you don't have to spend that much. You can get one for less than $50. Here's a link with some info.
http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/c892/

 

[David95436]

I have a Morningstar SunSaver controller between the battery and the rest of the DC system. When I called All Terrain, I was told to hook the inverter up to the battery directly, not to the controller.

Did I misunderstand them? Is it true that I may not hook the inverter up to the SunSaver? There is a place to connect the SunSaver up to "Load". Would that solve the problem?

If I can't hook the inverter up to the SunSaver, do I need a second controller (or something else) to protect the battery from the inverter?

 

[pods8]

I have a Morningstar SunSaver controller between the battery and the rest of the DC system. When I called All Terrain, I was told to hook the inverter up to the battery directly, not to the controller.

Did I misunderstand them? Is it true that I may not hook the inverter up to the SunSaver? There is a place to connect the SunSaver up to "Load". Would that solve the problem?

If I can't hook the inverter up to the SunSaver, do I need a second controller (or something else) to protect the battery from the inverter?


They are correct in telling you that unless you want to buy another controller. Although you are correct in concept that the sunsaver does low voltage disconnect for the battery, the problem is your 1200W inverter FAR EXCEEDS the 15amp rating for the load terminals on that controller. (1200W @ 12V = 100amps, @ 14V = 86amps). Here is the manual to that controller by the way: http://www.morningstarcorp.com/en/support/library/SSMPPT.IOM.EN.02.pdf

I'm sure there might be some product out there for you but to handle the amp ratings that inverter could pull they might be costly. Most likely some sort of relay would be needed but I'm not versed enough to detail out exactly all that would be needed.

Is this inverter for occasional use items like a microwave or something?(whatever it is if you plan to pull high wattage out of it you're not going to be running it a long time unattended) You'll probably just need to keep an eye on the battery voltage with a voltmeter after each time you use it.

 

[HERR42]

pods is right...that inverter must go directly to the battery.

since it draws over an amp while idle you will want to keep it shut off when not in use.

 

[David95436]

The main item using wattage is an 750W electric kettle to boil water. I may boil water five or six time in a day. If I knew the formulas, I could calculate how much power I use compared to the capacity of the battery to see if there is a theoretical possibility of drawing the battery down below 50%. There also may be an electronic device that could calculate how much electric y I am using per day to compare that to the battery capacity. Experts anywhere, please help.

The volt meter is a good idea, but I want to make this idiot proof. Perhaps a second controller will work, but I hate to spend the money. I don't think any inverter has this capacity.

 

[HERR42]

why not use propane? no stove?

 

[pods8]

The main item using wattage is an 750W electric kettle to boil water. I may boil water five or six time in a day. If I knew the formulas, I could calculate how much power I use compared to the capacity of the battery to see if there is a theoretical possibility of drawing the battery down below 50%. There also may be an electronic device that could calculate how much electric y I am using per day to compare that to the battery capacity. Experts anywhere, please help.

The volt meter is a good idea, but I want to make this idiot proof. Perhaps a second controller will work, but I hate to spend the money. I don't think any inverter has this capacity.


Well if you want rough numbers with some assumptions: 750W/12V = 62.5amps, lets say 85% efficiency in the inverter to be conservative = ~78amps when you plate is running at full rip. 60min of doing that burns 78amp/hrs.

How you're going to turn that into idiot proof I don't know, esp when you don't want to spend money. Personally I'd just monitor voltage levels (you can get volt meters that constantly display the voltage out in the open). Or maybe a low voltage alarm. But off hand I don't see doing a low voltage cutout quickly/easily without some money for components and knowledge of how to rig it all up. (edit: there are amp meters that monitor what you used but again you have to do something about it, they don't just cut out for you, so at that point its easier just to rely on voltage).

Maybe there is an easy answer out there for you but I don't have it.

why not use propane? no stove?


This too obviously.

 

[David95436]

My battery is rated 75AH which I assume is 75 Amp Hours. If Pods8's assumptions are correct, then I would use about 100% of the battery every day, except that the batter would be slowly charging in the sun. I don't know how long it takes the panel to charge the battery.

I have a stove, but I want to move towards everything solar for several reasons.

I think the volt meter or the alarm may be the best option.

Thanks

David

 

[pods8]

My battery is rated 75AH which I assume is 75 Amp Hours. If Pods8's assumptions are correct, then I would use about 100% of the battery every day, except that the batter would be slowly charging in the sun. I don't know how long it takes the panel to charge the battery.

I have a stove, but I want to move towards everything solar for several reasons.

I think the volt meter or the alarm may be the best option.

Thanks

David


If in the course of your day you run it for 60min then yes you'd likely use up all the battery (this assumes its actually pulling a full 750W which might not be the case). However as you mentioned it gets complicated in that you're constantly charging with solar. Just do the same math for that to get an idea of your charge rate in FULL SUN.

Or just check the voltages and not stress about the numbers so much.

One suggestion though: On a sunny day I'd try to load most of your boiling if possible towards the mid morning time, that way during the sunny day the panels can bulk charge the batteries more easily and hopefully you go into the night with full batteries. This is as opposed to charging them up all day then running them down with boiling in the evening and then having to wait till the next day to top them up again. You get better battery life if they spend more time at full charge.

Obviously you'll need to do some trial and error on figuring you how much power your solar setup can make up verse how much boiling you want to do.

 

[bobg333]

I have a stove, but I want to move towards everything solar for several reasons.




I, of course don't know your exact situation, but, from an efficiency standpoint, DC electricity is about the worst way possible to make heat. You have huge losses between the solar panel and the boiling water. How about using a solar cooker to boil your water? (http://solarcooking.org/) It is fun, and fits with the high-tech/low-tech aspect of being an FWC owner. ~ Bob