# I have a question about voltage coversion

#### Apurv Aggarwal

Joined Nov 2, 2015
9
So I have to design a solar powered system with solar input 0-5 powering up 2 loads of 3v and 4.2 v.
Till now I've designed till 5v battery from a charge controller. how do i connect the loads to 5v battery so that they get the particular amount of voltage, despite of varying battery voltage. Also any other suggestions related to project will also be appreciated. Thank you

#### Ramussons

Joined May 3, 2013
1,371
The 4.2 Volt system should be able to handle 5 Volts. You may have to go in for a Switching Buck Convertor for the 3 Volt unit.

#### Apurv Aggarwal

Joined Nov 2, 2015
9
No, i need the exact voltage input, it's a task and i have to design accordingly :|

#### mcgyvr

Joined Oct 15, 2009
5,394
So you need to incorporate a 3V and 4.2V regulator possibly a buck-boost depending on the range of the battery voltage.

#### Apurv Aggarwal

Joined Nov 2, 2015
9
can you please help me with the battery i should choose and with buck booster. that would be really grwat. thanks

#### mcgyvr

Joined Oct 15, 2009
5,394
can you please help me with the battery i should choose and with buck booster. that would be really grwat. thanks
No as you haven't provided any necessary details..
battery capacity?
battery chemistry?
environmental conditions?
charge controller specifics?
solar system schematic?

#### Apurv Aggarwal

Joined Nov 2, 2015
9
see battery capacity isn't a issue and it can be anytime type of battery, and it should work between 10-40 C, see all that I have to design.
I've mentioned the exact question above in my thread starter, that's all the information given to us :|
we are allowed to leave the power specifs as load power isn't given

#### Apurv Aggarwal

Joined Nov 2, 2015
9
I also wanter to ask the output of charge controller, is it equal to the battery output voltage?

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#### ian field

Joined Oct 27, 2012
6,536
The 4.2 Volt system should be able to handle 5 Volts. You may have to go in for a Switching Buck Convertor for the 3 Volt unit.
When I read "4.2V" - I immediately think lithium cell.

A home brew SMPSU is unlikely to be precise enough for safety if its for charging a lithium cell.

There are various off the shelf chips for this, which is the recommended route.

My home brew e-cig charger uses a simple TL431 shunt regulator, a fixed installation would require a timed shut of to prevent float charging for long periods.

#### wayneh

Joined Sep 9, 2010
17,469
I also wanter to ask the output of charge controller, is it equal to the battery output voltage?
Which output are you referring to, the leads to the battery or to the load? The answer to both questions depends on the specifications of the controller, which you have not provided.

The battery will not charge unless it is supplied a higher voltage than it has on its poles.

#### Alec_t

Joined Sep 17, 2013
14,005
I also wanter to ask the output of charge controller, is it equal to the battery output voltage?
It will be somewhat above the battery internal voltage because of charging current flowing through internal resistance. But battery voltage depends on the state of charge and the battery chemistry, so a smart charger has to allow for this to charge a battery safely.

#### blocco a spirale

Joined Jun 18, 2008
1,546
it's a task and i have to design accordingly :|
In that case you should propose a solution, that's the point of the task. You need to do some research.

#### Apurv Aggarwal

Joined Nov 2, 2015
9
Can you guys post a whole solution kinda please, today is the last day, tomorrow i have to submit, it would be really great, it's really important to me

#### JSCV

Joined Oct 3, 2015
23
If it's so important to you, why you didn't start earlier ? You really asking us to do your home work ?
I think most of the people here can help but won't do the complete task.

- What did you come up with so far ? (Schematics)
- What do you have in mind ? (workings) (if no specs are given, create your own.)
- Block diagram would be nice too.

#### Apurv Aggarwal

Joined Nov 2, 2015
9
okay man so solar output is 0-5, i don't get what input voltage range of charge controller is and what volt battery i should use.
also i am thinking of using buck converter to regulate battery voltage to load voltage. thank you

#### Apurv Aggarwal

Joined Nov 2, 2015
9
also load power rating is not giver so battery capacity is not an issue, just the voltage rating

#### Apurv Aggarwal

Joined Nov 2, 2015
9
Is there a charge controller that can work with 0-5 volts and 5v battery?

#### JSCV

Joined Oct 3, 2015
23
What specifications does your charge controller has ? part number ? or link to datasheet ?
This datasheet will also tell you what kind of battery to use.

Edit : Look on the internet for a proper charge controller.

#### ian field

Joined Oct 27, 2012
6,536
okay man so solar output is 0-5, i don't get what input voltage range of charge controller is and what volt battery i should use.
also i am thinking of using buck converter to regulate battery voltage to load voltage. thank you