messing around with the icharger 208b

[KTP]

Today was nice and sunny in Seattle, so I decided to play around a bit with the icharger 208B and a 26 watt foldable Brunton Solaris solar panel I happen to have.

I hooked up the panel to the 208B then connected a Turnigy 5AH 4s lipo battery. Initially I had the charge rate at 3 amps.

Starting off, the icharger display showed the charging current climbing to about 1 amp, then it started to fall off, becoming steady at 0.4 amps. I pressed the button to see the input power and it was 4.9V at 1 amp. I then stopped the charging and adjusted the charge rate to 0.75 amps and it stayed there, with the input voltage steady at about 17 volts.

Hmm, so I don't think the icharger is going to work very well as a MPPT solar charger

It *does* have a nice input voltage range of 4V-32V, but it doesn't have the smarts to pick the best power point. The solar panel has an open circuit voltage of a bit over 20V and a short circuit current of 1.7 amps or so, but the maximum power point is going to be around 15.9V and 1.6 amps. It seems if the icharger thinks it can pull down the voltage to grab more current, then that is what it is going to try, but the panel will only give 7 watts or so full sun at 4V, where it would give a full 26 watts at 15.9V. Setting the charging current to a lower value sort of remedies this since then the icharger doesn't pull the solar panel voltage down so low, but in the case of passing clouds or hazy sky I don't think that is going to be a real solution.

niche product alert! time for someone to design a MPPT Lipo smart charger...maybe would be a good senior EE project for me actually...

 

[scoot]

Always had a mind to attempt this type of experiment with my icharger too. Now I have a basic frame of reference to go on thanx to you :wink: . So what I take from this is one would probably need at least a 100 watts or more of solar panel to accomplish any useful charging with the 208b... 2-5 amps into 24 - 30 volts would be nice for me. Don't you just love the versatility of those ichargers?

 

[KTP]

Well...thinking about it some more, there might be a way to set a fixed power point such that the icharger is forced to take a certain voltage and current...

If we created a circuit that would limit the current to 1.6 amps when it has a voltage greater than 15V and 1 amp when it has a voltage greater than 12V but less than 15V...eh..actually this is really just building a MPPT front end to the icharger and would probably require a microcontroller and some sort of switching buck current regulator. At that point, might as well go ahead and make the whole lipo charging in the same microcontroller circuit....

 

[mwkeefer]

KTP - In the options, change the charge power watts - this will give you constant power limit regardless of input voltage - if it's enough.

Another is a voltage cutout so it will stop when the input voltage falls too low.

I have a new one here too after smoking all the FETs (I didn't do it, just happened) on my iCharger 1010B+ I grabbed one of these... Charged up a 6S3P pack fine but balked about low cell voltage with a 5S 3P pack - going to need to check my breakout board.

-Mike

 

[KTP]

KTP - In the options, change the charge power watts - this will give you constant power limit regardless of input voltage - if it's enough.

Another is a voltage cutout so it will stop when the input voltage falls too low.

-Mike

I am not sure what you mean by changing the charge power watts. If I tell it to charge a 4s pack at 1 amp it is already just about providing a constant power limit (the lipo starting at 14.8V and ending at 16.6V (4.15V per cell).

Changing the voltage cutout would just stop the charger....that wouldn't be very good if a cloud passes the sun...then I would have to know to go press charge again when the sun came out.

What I want is for the icharger to charge the battery at 2 amps when I have full sun, and drop back to 1 amp or 0.5 amps if the solar output is not full. I don't want the icharger to pull down the panel voltage to 4V because it seems to stay at that voltage and suck the maximum 1.7 amps (or about 7 watts) when it could be sucking 1.6 amps at 15.9V (26 watts). Maybe I need to do more testing to verify that it really is doing this...

 

[mwkeefer]

KTP,

Let me elaborate...

If there is some dangerous low voltage for your Solar Panel, use that as the input voltage cutout.

In the settings menu, change Charge Power to AUTO

Instead of setting the charge current, change to AUTO (I think it has auto ) which will adjust the charge current dynamically...

I do think I follow what you want but I should warn you... The iChargers are designed to work from a relative Constant Voltage supply which is why they drag down the voltage - the low input voltage is for charging off a battery...

Another suggestion - calculate approx the maximum watts of power you can charge (assume 90% efficiency of iCharger) and go configure charging power in settings to that wattage... That may work as you desire, providing higher current output in full sun but tapering when the input voltage drops.

Honestly - if your panels output a maximum of 17v under load and 3A per panel in full sunlight... I'd just configure a CV regulator for the solar panel - my dad has these on each panel they ensure voltage stays constant while current available changes.

-Mike

 

[liveforphysics]

I don't have a 208b in front of me to check the software, but the 3010b has a minimum voltage input setting. You could set it for 16v, and it will back off charge power to not let it drop below that point.

 

[whatever]

this video explains a bit about this
http://salebatterycharger.blogspot.com/2011/10/mppt-vs-pwm-solar-charger-achievement.html

i think an elcheapo mppt will do the job to keep the voltage up and improve output to the battery being charged

 

[NeilP]

Or just connect a small SLA between panel and iCharger..and also set the minimum input voltage as per other posts.. SLA can give you a bit of a buffer when charging starts..Use SLA as intermediate charge storage

 

[theRealFury]

couldnt you just hook up a DC/DC converter such as the one Lyen sells to the solar pannels and set output voltage to 16V or something of the like. They are rated for 3amps so 1.6amps of solar should be fine for it and it would ramp the current supplied to the charger down as the solar wattage dropped i think so would cause the charger to back off the charge amperage automatically?

I suppose i could try it as i have a lyen DC/DC converter spare, an icharger 106b+ and a spare 20watt solar pannel... so if no one else has tried this before i get round to testing ill post my results.