Battery Questions

[Satoshi Deguchi]

Hello,

I have some battery related questions.

According to this website, connecting batteries in series increases the voltage and connecting them in parallel increases current. Does this mean if I connect two AA sized batteries in parallel, with a maximum discharge rate of 5amps, the maximum discharge rate will be 10amps?

Context:
I plan to modify one of my flywheel Nerf blasters using AA sized LiFePo4 batteries from the OutOfDarts shop. The biggest roadblock is finding AA sized (or any that aren't Li-Po) batteries that have 10+ amps of discharge to meet the demands of the Honey Badger motors (22amps for a pair according to a modder). I've made the decision to not use Li-Po due to my concerns about it's safety/stability.

 

[Diver300]

Does this mean if I connect two AA sized batteries in parallel, with a maximum discharge rate of 5amps, the maximum discharge rate will be 10amps?

Yes, that is correct.

I don't think that an AA battery will be much use at 5 A.

https://www.powerstream.com/AA-tests.htm shows discharge tests up to 2 A on AA size. For 22 A you will need many in parallel.

 

[technofreak]

Lithium ion batteries are available in higher ampere capacities.
when using batteries in parallel or series, all batteries need to be of same type, has same charge and same discharge rate.
When using rechargable batteries in series or parallel, better to use battery management circuit to regulate charge and discharge, monitor heating.

check this out.. Sparfun Article

 

[Satoshi Deguchi]

Yes, that is correct.

I don't think that an AA battery will be much use at 5 A.

https://www.powerstream.com/AA-tests.htm shows discharge tests up to 2 A on AA size. For 22 A you will need many in parallel.

Unfortunately not for my purpose, so far as I can tell. But knowing that wiring batteries in series will help, thank you!

 

[Satoshi Deguchi]

Yes, that is correct.

I don't think that an AA battery will be much use at 5 A.

https://www.powerstream.com/AA-tests.htm shows discharge tests up to 2 A on AA size. For 22 A you will need many in parallel.

I've done additional research and the current needed to run these motors I want to use is about 1A. I got confused with idle current and stall current.

Do you know where I can find AA (14500) sized battery trays wired in parallel that have two battery slots? I've only been able to find 18650 sized trays (attached image).

 

[Diver300]

You could put two of these side by side:-https://cpc.farnell.com/hawker-energy/bx0035/battery-holder-can-style-aa/dp/BT01735

 

[Satoshi Deguchi]

You could put two of these side by side:-https://cpc.farnell.com/hawker-energy/bx0035/battery-holder-can-style-aa/dp/BT01735

Unfortunately it doesn't seem like I can have these shipped internationally. But thank you for sharing the link, it will help while I look for similar trays.

 

[Satoshi Deguchi]

Unfortunately it doesn't seem like I can have these shipped internationally. But thank you for sharing the link, it will help while I look for similar trays.

I'm having a very hard time finding 14500 sized trays. I've only been able to find 18650 trays on Amazon.

 

[danadak]

Batteries in parallel :

Near ideal diodes :

https://www.ti.com/lit/an/slvae57b/slvae57b.pdf?ts=1690124596035&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM74610-Q1

https://www.analog.com/en/technical-articles/primer-on-powerpath-controllers-ideal-diodes-prioritizers.html

Regards, Dana.

 

[Satoshi Deguchi]

Batteries in parallel :

View attachment 142210

Near ideal diodes :

https://www.ti.com/lit/an/slvae57b/slvae57b.pdf?ts=1690124596035&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM74610-Q1

https://www.analog.com/en/technical-articles/primer-on-powerpath-controllers-ideal-diodes-prioritizers.html

Regards, Dana.

Both answers are confusing.

How does the battery charge itself in a parallel circuit? That doesn't make any sense. I'm also using rechargeable batteries and need to increase the current output, not the total capacity.


My circuit as is follows:

Batteries ---> Switch ---> Two Motors (Parallel) ---> Fuse ---> Back to Batteries

The fuse is in place to prevent frying the motors/batteries when the motors stall (blaster jams) and they draw their stall current, which is significantly higher than what the batteries can handle.

 

[Nigel Goodwin]

Both answers are confusing.

How does the battery charge itself in a parallel circuit? That doesn't make any sense. I'm also using rechargeable batteries and need to increase the current output, not the total capacity.

The two answers seem to be deliberately confusing?.

The more charged of the two batteries passes charge to the flatter one, until they are balanced - and as there's no current limiting high currents 'could' flow.

It's quite simple - they are perfectly safe to use in parallel, IF you do it properly - it's quite simple, use brand new batteries of identical type. You should never mix different types or makes of batteries, or old ones and new ones, either in parallel or in series.

Li-Ion batteries are supplied in a partially charged state, this is their optimal storage condition - and all should be pretty well identically charged. Often chargers for individual LI-Ion cells (often will accept 4 to 8 cells) can be set to charge/discharge cells to their storage settings, you could use that to balance identical cells that have been used individually - or you could charge them fully individually.

 

[Satoshi Deguchi]

The two answers seem to be deliberately confusing?.

The more charged of the two batteries passes charge to the flatter one, until they are balanced - and as there's no current limiting high currents 'could' flow.

It's quite simple - they are perfectly safe to use in parallel, IF you do it properly - it's quite simple, use brand new batteries of identical type. You should never mix different types or makes of batteries, or old ones and new ones, either in parallel or in series.

Li-Ion batteries are supplied in a partially charged state, this is their optimal storage condition - and all should be pretty well identically charged. Often chargers for individual LI-Ion cells (often will accept 4 to 8 cells) can be set to charge/discharge cells to their storage settings, you could use that to balance identical cells that have been used individually - or you could charge them fully individually.

To reiterate, only use identical batteries that have the same charge, fully charged. The batteries I'm planning to use are LiFePo chemistry and are protected cell (which is what I've been looking for!).

When using these batteries, I would only use them after being fully charged. I assume that is good and safe practice.

 

[Nigel Goodwin]

To reiterate, only use identical batteries that have the same charge, fully charged. The batteries I'm planning to use are LiFePo chemistry and are protected cell (which is what I've been looking for!).

When using these batteries, I would only use them after being fully charged. I assume that is good and safe practice.

Yes, and make sure you don't mix old and new batteries.

There is a certain degree of margin when putting cells in parallel, but best not to take any chances.

 

[rjenkinsgb]

I've done additional research and the current needed to run these motors I want to use is about 1A. I got confused with idle current and stall current.

Each time the motors are started, they will initially take the stall current & that will drop down to the idle current level as they reach their free-running speed.

For cell holders, search "Individual AA cell holders" and "Modular AA cell holders" - there are several makers who produce individual cell or clip-together holders; eg. this type of thing:

1028 | Keystone AA Battery Holder, Leaf Spring Contact | RS

uk.rs-online.com

https://uk.rs-online.com/web/p/battery-holders/6119576?gb=b

BX0035 | Bulgin AA Battery Holder, Leaf Spring Contact | RS

uk.rs-online.com

https://www.amazon.co.uk/HALJIA-Plastic-Battery-Holder-Storage/dp/B07MJG8P1P/ref=sr_1_5?keywords=AA+cell+modular+holder&qid=1690212563&sr=8-5

 

[danadak]

The ideal diode was for this :
Post #9

This prevents one cell that is higher V from charging into the other cell,
wasting precious energy, because of unnecessary charge path Pdiss in
internal battery resistance.


Also aids in sharing in that the cell with higher V will start by suppling load
until it discharges to the V of the weaker cell, then they both supply
current until exhausted or system turned off.

Ideal, or as near as ideal, type diode solution supplied because "normal" diodes
have way too much V drop, so battery effectiveness is compromised.


Regards, Dana.

 

[audioguru]

Are you looking at the online No-Name-Brand AA size batteries that have a USB charge jack in them?
They are low current and low capacity (their specs are lies) junk.

 

[Nigel Goodwin]

Are you looking at the online No-Name-Brand AA size batteries that have a USB charge jack in them?
They are low current and low capacity (their specs are lies) junk.

No, he's not - if you read the thread he's using 14500's, a lower capacity AA sized version of an 18650 - which obviously MUST not be used in place of an AA as they are 4.2V and not 1.5V. I have some LED torches that use them - which at the time was a problem, because I expected them to take 18650's, so had to order some 14500's just for the torches.

 

[Satoshi Deguchi]

Thanks to every who has helped me so far!

I need some clarification here. Is the total voltage and amperage listed correct? If it isn't, where did I go wrong?

Also, can you help me find a good and free circuit diagram build/simulator?

 

[rjenkinsgb]

Is the total voltage and amperage listed correct?

Series cell connections increase voltage, but the amperage stays the same.
Parallel connections increase current, but the voltage stays the same.

You have two, three cell 1A chains in parallel, so three cells at 2x current; 2A

The voltage would be just over 12V initially with fully charged cells, gradually reducing to roughly 10.5V by the time the battery was fully discharged.
(Basing the voltage on normal lithium cells).

 

[Satoshi Deguchi]

Series cell connections increase voltage, but the amperage stays the same.
Parallel connections increase current, but the voltage stays the same.

You have two, three cell 1A chains in parallel, so three cells at 2x current; 2A

The voltage would be just over 12V initially with fully charged cells, gradually reducing to roughly 10.5V by the time the battery was fully discharged.
(Basing the voltage on normal lithium cells).

Thank you very much for the clarification!