12V Solar Trickle Charger - 19.8V!

[kudos]

Hi,

I just bought a 12V solar trickle charger:

http://www.amazon.co.uk/Solar-Briefcase ... sim_auto_8

I took it outside, it's a sunny day today, and measured the voltage.

It's a steady 19.8V

Although I'm starting to get a feel for battery tech after learning about LiPo for my ebike, I don't understand why the voltage output from this unit is so high.

Can someone explain why its OK to charge a '12V' battery at 19.8V ?

I realise that 12V is nominal and reality will be higher, maybe 13-14V.

Presumably it's to do with inefficiencies in the trickle charging process?

Cheers,
Kudos

[Xanda2260]

19.8v is only the open circuit voltage ( in full sun it'll probably be nearer 24). Once the voltage has todrivea current (i.e. When charging a battery) the voltage will drop. If you short the wirse together, the voltage will drop to near zero. Slap it on a battery and it'll be around 14 ish.

[SamTexas]

... why its OK to charge a '12V' battery at 19.8V ?

It's ok because the 12V battery will never see 19.8V. 19.8V is the open voltage of the panel, meaning there is no load (nothing to consume the power provided by the panel). As soon as the battery is connected, the voltage will drop significantly. Example: Assume your 12V battery voltage is 12.40V and the panel's voltage is
19.80V when they are NOT connected. As soon as the connection is made the two voltages will equalize and the single resulting voltage will be around 12.50V depending on the capacity of your 12V battery. If you have a large battery (125Ah) the equalizing voltage might be just 12.45V. If the battery is small (10Ah) the voltage might end up at 12.65V.

[kudos]

Ah I see, thanks Xanda.

I just found pveducation.org

Voc occurs at zero current and voltage drops as current increases.

Another technology to learn!

Once I've got my next ebike on the road, I'm going to build a solar powered bike charging station.

Cheers,
Kudos

[Xanda2260]

You are most welcome

Sent using the might of the Android Army!

[Alastor]

Sent using the might of the Android Army!

lol

Also note that if this panel dose not have a battery charge controller if you connect it to your battery permanently you will surely damage it or worst case scenario burn her up .
Check this out in the panels specs to be on the safe side

[Jay64]

Wouldn't 4 watts be just about what it takes to maintain the battery from losing it's charge over time?

[Alastor]

Your little pannel in a full sunny day can produce up to 40to60 watt of power.if the pannel has no charge regulator you might overcharge and smoke the battery.make sure that you use a regulator or your pannel has one embedded to be sure cas an overcharged battery is like a bomb.