Maha 204F and 180ma input?

[BatteryCharger]

I've been lurking here for quite a while...seems like a good place to ask this question. /ubbthreads/images/graemlins/smile.gif I have a Maha 204F battery charger. I was thinking about getting one of those solar panels you use to keep your car's battery topped of, which puts out 12v @ 180ma. If I hooked that up to my charger, would it work, only slower?

 

[Brock]

Darn, I just gave my 204 to my brother since I use 401's now. I wish I could say for sure but I know the 401 pulls 20mA @ 12v per battery on low and 50mA per battery on high, or 80mA for all 4 on low and 200mA for all 4 on high. So it might work since the 204 is somewhere between the high and low setting of the 401. I would guess in full sun it would charge 4 batteries, and in partial sun I would stick with only 2 at a time. The problem is if a cloud passes over and your voltage drops the 204's charge controller will start over. If you could put even a small 12v gel cell in line you would be set, but that would add weight and size to the setup. In any case it shouldn’t hurt the charger, I would watch it and see how it performs.

 

[BatteryCharger]

Thanks brock - The 401 only uses 200ma to charge all 4 batteries on high?! On my 204F I know the "wall wart" is rated at 500ma, and it says in the manual about the car charger you need to connect it to a source capable of 500ma draw. Does the 401 say the same? I would like to just try it and see if it works, but I don't want to spend $25 on a solar panel for it to not work.

 

[zmoz]

[ QUOTE ]
Brock said:
The problem is if a cloud passes over and your voltage drops the 204's charge controller will start over.

[/ QUOTE ]

I've been thinking of doing the same thing. Would it really matter if it lost power for a while? Since the 204F doesn't work on a timer, what would it really reset?

 

[Brock]

The 401 comes with a 1000mA wall wart. I have mine connected to a HUGE 12v battery bank charged by solar panels so I don't use the wall wart. I think they tend to oversize the power supply's, probably because the 1000mA can put out 250mA constantly without overheating and 1000mA for 1 min or something like that.

zmoz, this is true. It is a "smart" charger, but it will start the charge process over and over if it regularly looses power. But since it is a smart charger it really shouldn't matter. I don't know if it would hurt the smart part though. Also if you disconnect a "green" 204 and power it back up it goes back in to charge mode, but usually jumps back to "green" in a matter of 5 min or so.

 

[shankus]

How picky it is about the input voltage? If you put a 9V battery in parallel with the panel, I wonder if that would keep it running correctly during a cloudover.

 

[Doug Owen]

[ QUOTE ]
Brock said:
Darn, I just gave my 204 to my brother since I use 401's now. I wish I could say for sure but I know the 401 pulls 20mA @ 12v per battery on low and 50mA per battery on high, or 80mA for all 4 on low and 200mA for all 4 on high.

[/ QUOTE ]

This is most interesting, and in this strange small world of ours I've been thinking along the same lines using a 24 Watt panel I just bought to fiddle with. However 'the numbers don't add up'. To fully charge AA NiMH cells we're talking say 2 Watt hours (1700 mAH times 1.2 Volts) even at 100% efficiency. 50 mA times 12 Volts is 'only' .6 Watts it would take at least 2/.6 or 3.3 hours. The 'manual' for my 401 says 1000 mA on high (100 minute), 300 on low (5 hours) charging current, in line with the expected charging performance, but about twice the current draw cited above (even at 100%)?

I just went looking for the car charger cord so I could measure it, but seem to have lost it (hopefully temporarily). I don't really want to cut the wall wart cord and have to live with the splice afterwards, does anyone else have the cord, and meter, power supply and a bit of time?

Doug Owen

 

[Brock]

Two more things I thought of.

First a solar panel usually puts out a slightly higher voltage so if it does get shaded a bit it is still above the rated voltage. For example a Siemens SP75, 75 watts at 12v, in full sun will put out 18v @ 4 amps. If you directly connect it to a battery it still puts out only 4 amps. I guess my point is the solar panel might actually be a higher voltage, and less wattage then you might hope for.

Secondly, Doug brings up a very good point, it is odd thinking about it now with the numbers I got. I should add my battery bank sits about 13.4vdc so in reality were looking at .05x13.4 or .67w Still to low to really charge the battery in 2 hours. hummmmm I metered it with my Fluke 87 III in average mode. In instantaneous it was all over the place up and down. I did only test it for about 2 min, I wonder if it starts pulling more power as it gets going? Or I wonder if since the batteries weren’t dead it didn’t put as much power in to them. I will have to meter more of them with different batteries to be sure, and for a longer time.

 

[Doug Owen]

[ QUOTE ]
Brock said:
Two more things I thought of.

First a solar panel usually puts out a slightly higher voltage so if it does get shaded a bit it is still above the rated voltage.

I did only test it for about 2 min, I wonder if it starts pulling more power as it gets going? Or I wonder if since the batteries weren’t dead it didn’t put as much power in to them. I will have to meter more of them with different batteries to be sure, and for a longer time.

[/ QUOTE ]

Spot on on the second point. So I broke down and cut the cord. It does indeed start low and 'all over the place' in a series of two or so second pulses averaging maybe 80 mA per cell? and changing in duty cycle as more cells are brought on line. However, about two minutes into it it 'changes into high gear', 850 mA for four on high, 280 mA for four on low. Makes sense now.

The 'need more voltage than 12' is because the cell voltage isn't constant, it goes up a bit with more sun. It's my understanding that the rating is 'full sun' current (1000 Watts to the square meter incident) at the *nominal* output voltage for the panel (even if it's reading higher). "Specsmanship" doesn't seem to be routine in this industry? However, if shaded even a little bit, they crash. The cell in shadow becomes an open, current drops to near zero. A real problem on boats where it's not possible to aim them so they're mounted flat and have to deal with shadows from the rigging when the sun is overhead (the only time they'll work well anyway).

BTW, other interesting numbers for these are 13% or so maximum efficiency (makes the panel power to size make sense) and anywhere from 42 to about 50% of the total daylight hours times ratings for expected output by a well aimed panel at the NY/SF type latitudes (37 or so degrees). Other 'experts' say to design around 5 hours output at full power for good days. Meaning my new 24 Watt panel should produce something like 100 to 125 Watt hours per day. More or less. FWIW it has 36 cells (33 or so seems to be the absolute minimum for serious 12 panels, you need to count, panels with less can be chronically under voltage to recharge lead acid batteries).

I still want to know how many AA NiMHs my Maha 401 being powered by my brand new 24 Watt panel can charge in a typical day.....

Doug Owen

 

[highlandsun]

Just think of a solar cell as a really really weak battery. Open circuit voltage is much higher than operating voltage; the voltage plummets when you apply any load. When I bought my 4W cell to power my Atari Lynx, I got a panel with a ~14V OCV. Plugged into the Lynx it dropped to about 8V, with enough current to keep it happy.