Date: Fri, 19 Apr 2013 20:51:22 -0500
Reply-To: tom ring <taring@TARING.ORG>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: tom ring <taring@TARING.ORG>
Organization: Tippen Ringware
Subject: Re: Solar controller question..semi off topic.
In-Reply-To: <516E245E.8000706@colorado.edu>
Content-type: text/plain; charset=US-ASCII
Yep, MPPT is the way to go. I have 180 watts on my van and use an MPPT
controller.
The big difference is this -
Simple on/off controller is roughly 40% efficient
Pulse width might get you 50%
A decent MPPT can get you 90 to 97%
MPPTs do a magic thing - their power in is almost equal to power out but the
volts and amps are fiddled with. So 18 volts (roughly where solar panels are
most efficient) at 12 amps input can be converted to almost 18 amps at 12 volts
charge current (where the battery might want a charge right now). And they
adapt to power delivered and charge needed second by second.
An MPPT at $250 is roughly equal to about the cost of a good 90 or 120 watt
panel and can save you that much or a lot more in solar panel money spent.
I currently use a Solar Boost 2000e which will handle 25 amps and is 94 to 97%
efficient for my system. It also will equalize the battery system, has
temperature compensation and can be set for optimum base battery voltage.
And on amps, make sure when you size an MPPT controller you pay attention to
whether it's X amps in or X amps out. I bought a cheap one ($100) for my 180
watts of panels and neglected to pay attention to that. It was 10 amps in but
ended up almost 15 out which burned up the 10 amp out MPPT controller.
I can't say too many good things about Solar Boost products. They are great.
One disclaimer, if you are a ham radio operator and run HF from the van, buy
some decent ferrite chokes, these things can be a bit noisy.
tom
On 16 Apr 2013 at 22:26, Richard Jones wrote:
> > What do these numbers all mean? Anyone
> > want to give me a quick bit of advice on this?
>
> Don:
>
> [I'll reply on-list since others are thinking of solar.]
>
> Add the watts of your panels and get a controller that
> has a rating that is higher. In your case, 75+40 = 115,
> so your second choice of 127.5 watts is enough. It
> doesn't hurt to go higher, just the cost is a little
> more.
>
> There are several technologies in solar controllers. A
> while back there was only pulse-width. When the battery
> got fully charged, the controller shut off/on to give the
> batteries a pulse that kept them full. I am still running
> one of these (Blue Sky) from ~8 years ago in a high mtn
> cabin PV light system. Works....
>
> Then MPPT came along. As you saw, you can get 21 volts out
> of a 12 V panel--sometimes. Older controllers just took
> 12V and ignored the rest. MPPT controller take the full
> voltage from the controller and convert it to 12V at a
> higher amp (or wattage) rating than the panel, so you get
> more power out of the panel. Most MPPT controller claim
> ~30% more power. So MPPT is your friend.
>
> I bought a 10 amp MPPT from ebay recently for ~$25. Here
> is the same thing for $19. I figure you can't go wrong to
> that price. I have not used mine enough to say if it is a
> good controller or not, but it is working.
>
> http://www.ebay.com/itm/10A-15A-20A-30A-MPPT-Solar-Panel-Regulator-Charge-Controller-12V-24V-Auto-Switch-/310639824059?pt=LH_DefaultDomain_0&var=&hash=item4853938cbb
>
> A good site to learn is windsun.com, part of Northern Arizona
> Wind & Sun. Here's a page on MPPT:
> http://www.solar-electric.com/whatismppt.html
>
> I'd say that with 115 watts, which is ~8+ amps, you should
> have plenty of solar capabilites to keep whatever you want
> charged and running--unless you are using an inverter to
> run one of Terry Key's window AC units. ;-)
>
> Richard
>
-----------------------------------------
Tom Ring K0TAR EN34hx
Never attribute to engineers that into which politicians, lawyers,
accountants, and marketeers have poked their fingers.
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