I'm trying to utilise a 70 Volt solar panel output which puts out 800mA at peak.
I'm playing with these
http://www.ebay.com.au/itm/251309504912?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

but their input is only 250mA.
I will be feeding a 12Volt battery system .
How is the best way to limit what I feed into this device to a max of 250mA?
I thought I might buy 3 more and connect them in parallel as a final solution if it works well

 

Is there a reason why you're contemplating building such an inefficient system? You'll be throwing away most of the power generated by the solar panel.

Can the panel be reconfigured to give you more current at an appropriate voltage? Can the panel be tapped at a more appropriate voltage?

 

I'm trying to utilise a 70 Volt solar panel output which puts out 800mA at peak.
I'm playing with these
http://www.ebay.com.au/itm/251309504912?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

but their input is only 250mA.
I will be feeding a 12Volt battery system .
How is the best way to limit what I feed into this device to a max of 250mA?
I thought I might buy 3 more and connect them in parallel as a final solution if it works well
View attachment 121338

The panel is not going to "put out" 800ma unless it is being consumed. You can safely connect your switching power supply without issue.

 

And the power supply you have linked can only supply 250ma to your load. The 250ma rating has nothing to do with a limitation on its input current.

Plus it is doubtful your panel is really capable of 70v/ 800ma in the real world anyway. assuming that is the manufactures rating. Those numbers are under ideal conditions.

 

How is the best way to limit what I feed into this device to a max of 250mA?

This is a recurrent theme on electronics websites. People ask every few weeks, "The local electric company generates 130,000 amps. How can I limit the power going to the light bulbs in my house?"

Think about it.

"My solar panel might produce more current than my load needs. How do I limit the solar panel from forcing all its amps into my load?"

 

I will be feeding a 12Volt battery system .

If you're talking about a lead-acid battery, they need more than 12V to charge properly. If that device really delivers 12V, it won't charge a 12V battery very well. You need at least 13.8 to trickle and more like 14.5V during bulk charging.

As the other answers have noted, the current is determined by the load, not the source, as long as the voltage is within its specifications.

 

This is a recurrent theme on electronics websites. People ask every few weeks, "The local electric company generates 130,000 amps. How can I limit the power going to the light bulbs in my house?"Think about it.
"My solar panel might produce more current than my load needs. How do I limit the solar panel from forcing all its amps into my load?"

A flat set of 12 Volt batteries in my system will draw up to 30 amps then the current will slowly fall as the voltage rises . If I connect this device with the panel supplying current it will draw everything it can will it not ?

I can and do charge my batteries at 13.8 V but not for long I can assure you otherwise the batteries sulphate and the acid boils off . These people who advise you to charge at rates over that have just never done flooded lead acid batteries apart from their car!

 

A flat set of 12 Volt batteries will draw up to 30 amps in my system then the current will slowly fall as the voltage rises .
If I connect this device with the panel supplying current the battery bank will draw everything it can ,will it not ?



I can charge my batteries at 13.8 V and do, but not for long I can assure you otherwise the batteries sulphate and the acid boils off . These people who advise you to charge at rates over that ,have just never done flooded lead acid batteries, apart from their car!

Each cell is 2.2V fully charged or 12.7V in a bank of 6 cells in series . Push them over that and you damage them. Simple as.

If I am charging at 13.8 volts I am half a volt over my optimum limit so I monitor the actual battery voltage to make sure it does not exceed 12.7Volts .Period.



Chart from battery university site .

 

this is a ridiculous forum cant do this , cant do that ,10 minutes to get your post right . I might make 4 to 10 corrections to my post to present it the way i want it Not much good to me i think

 

this is a ridiculous forum cant do this , cant do that ,10 minutes to get your post right . I might make 4 to 10 corrections to my post to present it the way i want it Not much good to me i think

You post a misconception of how electricity works in your first post and somehow that is the "forum's" fault? And then you post 2 subsequent follow up posts (with no one asking for more details) and somehow that is the "form's" fault too?

 

See another one of Bob's posts.

https://forum.allaboutcircuits.com/...-boards-how-do-they-work.132570/#post-1099150

 

If it walks like Billy Mayo, and sounds like Billy Mayo, it just might be Billy Mayo.

 

this is a ridiculous forum cant do this , cant do that ,10 minutes to get your post right . I might make 4 to 10 corrections to my post to present it the way i want it Not much good to me i think

Probably not, but l will try. To limit input to your solar panel (as you asked in the title of the thread) cover it with paper or something similar to block the sun's rays.

 

If it walks like Billy Mayo, and sounds like Billy Mayo, it just might be Billy Mayo.

Or Jay Gatsby or anyone of the other personas.

 

,10 minutes to get your post right . I might make 4 to 10 corrections to my post to present it the way i want it Not much good to me i think

Most people would have gotten it right the first time. It is somehow our fault you can't put your thoughts together in a form it can be understood by others?

 

I can and do charge my batteries at 13.8 V but not for long I can assure you otherwise the batteries sulphate and the acid boils off

Sulfation is minimized by "hard" charging for at least 2 hours before switching to trickle/float charging.

Here's an often quoted article on charging lead acid batteries:
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

 

See another one of Bob's posts.

I had not even checked that Thread to see how it was progressing. (Too busy doing winter chores in Florida.)
Thanks for pointing to it.

 

Each cell is 2.2V fully charged or 12.7V in a bank of 6 cells in series . Push them over that and you damage them. Simple as.

Your own chart clearly shows a float charge of at least 2.25V, which gives 13.50V. But at this level of detail, specifying battery temperature is critical because the ideal voltage varies with temperature. If I keep my boat's battery at 12.70V all winter, it won't start the boat come spring. At 13.80V, away I go.

 

How is the best way to limit what I feed into this device to a max of 250mA?

The simplest technique is a resistor from this device in series to the battery. For instance at 13V and a current of 250mA, a resistor of 13/0.25 = 52Ω will prevent the current to the load (the battery) from ever being more than 250mA. This is not terribly efficient but you haven't defined "best".

 

I can and do charge my batteries at 13.8 V but not for long I can assure you otherwise the batteries sulphate and the acid boils off . These people who advise you to charge at rates over that have just never done flooded lead acid batteries apart from their car!

You must have really bad cheap batteries or a very bad meter you are reading your voltages with.

I charge 12 volt Lead Acid based batteries in every size form 3 - 5 AH to 250+ AH pairs at 14.5 - 15 volts with chargers that can supply literally hundreds of amps if needed often for days at a time without problems.