# 12 V battery charger from 75V solar panel

Discussion in 'Power Electronics' started by David Soltz, Aug 6, 2014.

1. ### David Soltz

1
0
Aug 6, 2014
Hi,

I would like to make a 12V lead acid battery charger (DC) from a solar panel that produces something like 75V and 1A.

Could anyone offer some suggestions as to what components I need to get to convert the voltage, and regulate the charging of the battery?

Looking to spend around \$50 or less if possible.

Thanks,

Dave

2. ### davennModerator

13,786
1,937
Sep 5, 2009
hi David

welcome to EP

I wonder if that is open circuit or loaded voltage ?
The voltage that is usually stated for a panel is its open circuit voltage and it will drop a bit under load
if it's really around 75V, it's not likely to drop to anything under approx 50 - 55V under load

Do some google searching on BUCK CONVERTERS and see if you can find one that will take up to 75V input and still give your required output of around 14V
Yes 14V, you need at least that to charge a 12V lead acid battery correctly

Dave

5,165
1,087
Dec 18, 2013
Are you sure it's not 75 Watt at 12 Volts. That's a common solar panel wattage. And the common nominal voltage is 12 Volts but will rise to about 17 Volts in full sun. So do you have one 12 Volt panel or 6 in series? Which would give you more than 70 Volts. Or is it something else, one massive panel. Do you have a datasheet for it we can see?

Last edited: Aug 6, 2014
4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,481
2,830
Jan 21, 2010
And once you confirm the open circuit voltage, the thing you're looking for is a MPPT charger.

From your perspective, the most important specifications are the maximum input voltage (it must exceed your solar panel open circuit voltage) and the battery voltage (it must match your battery).

A buck converter can fail badly if too much power is demanded from a solar array. It can cause the panel to be effectively short circuited. This is not a problem for the panel or anything else, but it reduced the power available from the panel hugely.