Swapping a 150 mah battery to a 600 mah when charging circuit only 20ma?

Thread Starter

OldNewb

Joined Jun 8, 2014
9
Gentlemen, I have a quick question regarding the little cheap solar garden lights. I have one that came with a AA nimh 150mah battery. I measured the charging circuit current output to be only 20ma. What would happen if I put a 600mah battery (same size, same voltage, same chemistry-nimh) in place of the 150mah one? Or maybe my question I should be asking is how to increase the charging circuit output to match the 600mah battery?
 

KeithWalker

Joined Jul 10, 2017
1,789
Gentlemen, I have a quick question regarding the little cheap solar garden lights. I have one that came with a AA nimh 150mah battery. I measured the charging circuit current output to be only 20ma. What would happen if I put a 600mah battery (same size, same voltage, same chemistry-nimh) in place of the 150mah one? Or maybe my question I should be asking is how to increase the charging circuit output to match the 600mah battery?
If the maximum current from the solar cell is 20mA, it can only supply about 150mAH on a good sunny day. The only way you can get more is by using a larger solar cell, or several connected in parallel.
 

Audioguru again

Joined Oct 21, 2019
3,201
A Ni-MH battery cell that is AA size is 2300mAh when it is a Name-Brand one. Your 150mAh cell is probably from China is mostly full of rice. Your 600mAh cell is 75% rice.

I have many solar garden lights and have replaced all of the cheap battery cells before they rust away in a couple of months.
The 2300mAh cells work much better for many years.
 

MrAl

Joined Jun 17, 2014
8,253
Gentlemen, I have a quick question regarding the little cheap solar garden lights. I have one that came with a AA nimh 150mah battery. I measured the charging circuit current output to be only 20ma. What would happen if I put a 600mah battery (same size, same voltage, same chemistry-nimh) in place of the 150mah one? Or maybe my question I should be asking is how to increase the charging circuit output to match the 600mah battery?
Hi,

A solar cell or solar panel has a maximum power point on it's current/voltage curve. If it is operating at that point and the voltage is too high for the battery cell then you can use a buck circuit to step down the voltage which in turn makes the current higher.
But it';s hard to tell if this will work wth a solar cell or panel that we dont have any specs on, and with something this small it would probably be just as easy and cheap enough to just get another solar cell or panel that can put out more current. I would think 30ma minimum but 50ma better. 20ma might charge it but may take too long and the full sunlight is only present for a short time during the day.
So probably the best bet is to get a larger panel. If you get one that is much bigger (putting out much more current) then it may charge better in lower sunlight levels also. Just have to watch out for over charging then.

If you have 6 hours of sunlight then 120ma should be ok.
 

Audioguru again

Joined Oct 21, 2019
3,201
You do not need a larger solar panel. Old solar garden lights had a cheap solar panel with a plastic cover that got sunburned after a few months. New solar garden lights have a good quality solar panel with a glass cover and they work well for years.
The replacement 600mAh battery cell has the same chemistry and same voltage as the original 150mAh one so the light might glow for a longer time each night and it might even light the night following a cloudy day.
 

Thread Starter

OldNewb

Joined Jun 8, 2014
9
If the maximum current from the solar cell is 20mA, it can only supply about 150mAH on a good sunny day. The only way you can get more is by using a larger solar cell, or several connected in parallel.
I was thinking somewhere I read changing the inductor in the circuit would change the output but I see what your saying. Maybe it was talking about the output to the led being lowered to make it burn longer into the night. Even I could create and charging circuit capable of 80ma output, it wouldn't be able to because of the solar cell itself being the limiting factor. Thank you sir!
 

Thread Starter

OldNewb

Joined Jun 8, 2014
9
A Ni-MH battery cell that is AA size is 2300mAh when it is a Name-Brand one. Your 150mAh cell is probably from China is mostly full of rice. Your 600mAh cell is 75% rice.

I have many solar garden lights and have replaced all of the cheap battery cells before they rust away in a couple of months.
The 2300mAh cells work much better for many years.
Sorry the actual battery size is 2/3 AA (shorter than regular AA)
 

Thread Starter

OldNewb

Joined Jun 8, 2014
9
Hi,

A solar cell or solar panel has a maximum power point on it's current/voltage curve. If it is operating at that point and the voltage is too high for the battery cell then you can use a buck circuit to step down the voltage which in turn makes the current higher.
But it';s hard to tell if this will work wth a solar cell or panel that we dont have any specs on, and with something this small it would probably be just as easy and cheap enough to just get another solar cell or panel that can put out more current. I would think 30ma minimum but 50ma better. 20ma might charge it but may take too long and the full sunlight is only present for a short time during the day.
So probably the best bet is to get a larger panel. If you get one that is much bigger (putting out much more current) then it may charge better in lower sunlight levels also. Just have to watch out for over charging then.

If you have 6 hours of sunlight then 120ma should be ok.
I am finding that the circuit was designed to charge a 150mah battery. I calculate it would take 9hrs of full sun to charge a completely empty 150mah at 20ma charge current. A 600mah would required 80ma charge rate on 9hrs full sun. So I going to put the 150mah batteries that came with the light back in it so it will at least come back up to enough voltage to turn the light of a dusk. The 600mah ones don't even charge up enough to even turn on at dark.
 

Thread Starter

OldNewb

Joined Jun 8, 2014
9
Gentlemen, I have a quick question regarding the little cheap solar garden lights. I have one that came with a AA nimh 150mah battery. I measured the charging circuit current output to be only 20ma. What would happen if I put a 600mah battery (same size, same voltage, same chemistry-nimh) in place of the 150mah one? Or maybe my question I should be asking is how to increase the charging circuit output to match the 600mah battery?
That is what I believe now. What confused me is people on youtube where saying "upgrade your ni-cads to a ni-mh with higher capacity." That might work on some of the nicer lights, however not the cheapo dollar store lights. I am thinking some chinese company got stuck with a large quanity of 2/3 AA 150mah batteries and had somebody design the crappiest light in the world that would work for at least a short while and be able to use that inventory up at a reduced loss. Some nicer light have outputs of 52ma ,82ma, 100ma, 200ma, up to 350ma on some. I think I am just going to build my own circuit and use some 18650 li-ions with quality parts and then just keep them clean and maintained regularly.
 

MrAl

Joined Jun 17, 2014
8,253
I am finding that the circuit was designed to charge a 150mah battery. I calculate it would take 9hrs of full sun to charge a completely empty 150mah at 20ma charge current. A 600mah would required 80ma charge rate on 9hrs full sun. So I going to put the 150mah batteries that came with the light back in it so it will at least come back up to enough voltage to turn the light of a dusk. The 600mah ones don't even charge up enough to even turn on at dark.
Do you happen to know if that 20ma was when it was new also or just because it is an old system?
Yeah 80ma sounds good if you have a solar director mechanism in place. If not, it would be wise to go with a higher rated solar panel. 9 hours of sunlight does not mean max current for 9 hours because the power decreases with the angle of the sun relative to the surface angle of the solar panel. I dont know much about your actual setup though would be nice to see a couple pics :)
 
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