# Battery and powersupply

#### reuven91

Joined Nov 17, 2017
6
Hello
I'm new here but I believe I'll stick in for a long time
I've joined a project to build a space suit for research purposes. I've been asked to plan the power supply for the suit. The suit is going to have a fan to vent CO2, a two way radio (currently it's going to be a walkie talkie that needs to be connected directly to the power supply instead of its native battery), and possibly a raspberry pi and a few LEDs. The suit is going to run on a battery. Now, I'm wondering: what would be the best way to connect all the above apparatus to the battery? should we get a power supply unit or something else?
note: I'm a second year electrical engineering student, I have some basic knowledge of electricity but I'v never planned anything like this.

#### nsaspook

Joined Aug 27, 2009
6,596
Usually the first thing is to develop an energy budget for what's needed for normal operation plus a safety margin. This means for each consumer (devices powered from the suit) of power you need to detail all voltage and current requirements (for power calculations) into some sort of list to have some idea about the size of battery needed.

#### wayneh

Joined Sep 9, 2010
16,128
In space you don’t need a fan to exhaust...anything. Just a hole.

#### reuven91

Joined Nov 17, 2017
6
Usually the first thing is to develop an energy budget for what's needed for normal operation plus a safety margin. This means for each consumer (devices powered from the suit) of power you need to detail all voltage and current requirements (for power calculations) into some sort of list to have some idea about the size of battery needed.
Yes, I'm currently waiting for an answer about the fan. I already know the model of the walkie talkie - it's Cobra MT645 (They use x3 simple AAA batteries) so I can estimate its consumption and search for the power consumption of a raspberry pi. What would be the next step after all those estimations?

In space you don’t need a fan to exhaust...anything. Just a hole.
haha that's true!
But those suits are planned to be used in a desert here on earth. They're made to imitate future Mars missions. We're also working on a basic habitat that's going to be built by February

#### nsaspook

Joined Aug 27, 2009
6,596
Yes, I'm currently waiting for an answer about the fan. I already know the model of the walkie talkie - it's Cobra MT645 (They use x3 simple AAA batteries) so I can estimate its consumption and search for the power consumption of a raspberry pi. What would be the next step after all those estimations?
Once you have the power requirements it's time to prioritize and optimize. The fan might be the #1 priority due to the environment so I would look for the most efficient (electrical and weight) direct combination of fan and battery voltage so it's possible to use a direct connection with little or no electronics to make it work if needed in a emergency with a simple direct connect bypass switch.

#### reuven91

Joined Nov 17, 2017
6
Once you have the power requirements it's time to prioritize and optimize. The fan might be the #1 priority due to the environment so I would look for the most efficient (electrical and weight) direct combination of fan and battery voltage so it's possible to use a direct connection with little or no electronics to make it work if needed in a emergency with a simple direct connect bypass switch.
I see, so turns out fans have startup voltages higher than operating voltages, so I'll have to figure out what is the best way to connect it and then let the team know what voltage specifications are better.

#### MrChips

Joined Oct 2, 2009
19,755
I see, so turns out fans have startup voltages higher than operating voltages, so I'll have to figure out what is the best way to connect it and then let the team know what voltage specifications are better.
No. The voltage can remain the same. It is the current drawn that has a surge on startup. Once the fan is running the current drops. If you put a heavier load on the fan the current will go up.

#### reuven91

Joined Nov 17, 2017
6
No. The voltage can remain the same. It is the current drawn that has a surge on startup. Once the fan is running the current drops. If you put a heavier load on the fan the current will go up.
Ok I see. so say I connect a 12V fan directly to the battery. How would I connect the other components if they have different operating voltages?
is there some kind of device that you can connect the battery to, to get multiple connections?

#### nsaspook

Joined Aug 27, 2009
6,596
Ok I see. so say I connect a 12V fan directly to the battery. How would I connect the other components if they have different operating voltages?
is there some kind of device that you can connect the battery to, to get multiple connections?
Sure there are devices that do that but do we get the credit for designing the space suit for you or will you do a little research on the subject?

#### reuven91

Joined Nov 17, 2017
6
Sure there are devices that do that but do we get the credit for designing the space suit for you or will you do a little research on the subject?
Believe me I'm trying, but it's a little hard searching for a device that I don't know the name of, especially as English is not my native language. If you don't want to help, don't.
Thanks anyway

#### Dodgydave

Joined Jun 22, 2012
8,586
If your battery is of a bigger voltage than needed, then use voltage regulators to drop down the voltage for the other items, ideally ready-made ones like Lm2576 types..