Battery data sheet help

[TEO]

Hi all, I'm trying to figure out the data sheet for the batteries on a powered wheelchair.
Can anyone tell me what the rated values mean please? In very basic terms pls?
I'm trying to find a pair of batteries that will take the place of this pair but halving the weight. If I halve the weight I'm expecting to have halved the power but that's where the questions start; will there still be enough usable power?

 

[voipio]

What's the specification for the existing batteries? Are they also 12V, 20Ah?

 

[TEO]

What's the specification for the existing batteries? Are they also 12V, 20Ah?

Sorry, the spec sheet above is for the OEM batteries supplied with the chair. Pic of OEM batteries attached to this post.
& I'm looking to get an idea of the runtime of the OEMs batteries so that I can judge whether in halving the weight we're still going to have a useable range. I imagine that the range/run time with the OEM batteries is way beyond our requirements. I'll post pics of the motors soon & questions about the motor controllers.

 

[jsf55]

Quick look here https://www.tayna.co.uk/mobility-batteries/types/19ah/ i found i struggled too get a 20ah for the brother in laws jump pack, so just went of the sizes instead, i think it was a 19ah
Edit, look at the Lucas pdf it has the weights

 

[TEO]

Quick look here https://www.tayna.co.uk/mobility-batteries/types/19ah/ i found i struggled too get a 20ah for the brother in laws jump pack, so just went of the sizes instead, i think it was a 19ah
Edit, look at the Lucas pdf it has the weights

Thanks, I'll have a look

 

[voipio]

Wheelchair batteries should be of the deep discharge type, which means they contain much more robust electrodes, that can take multiple deep discharges without them falling apart. The lighter weight batteries might perform reasonably well over the first few charge discharge cycles, but will lose capacity quite rapidly thereafter. Or are you thinking of installing lower capacity deep discharge batteries?

 

[GRW]

Those batts are probably considered to be 28ah (as they tend to use the C20, 20-hr value for classifying.... cos 28 is more than 20.
So a 19ah batt also rated at C20 is considerably less.
Something to be aware of.

 

[J1nx]

I assume the batteries are in series then? Otherwise you could just remove one to get the result your after

 

[m_c]

Halving the battery capacity will likely more than half the run time, due to internal resistance and the batteries being worked relatively harder.

Are you trying to reduce replacement cost, or weight?

 

[TEO]

Wheelchair batteries should be of the deep discharge type, which means they contain much more robust electrodes, that can take multiple deep discharges without them falling apart. The lighter weight batteries might perform reasonably well over the first few charge discharge cycles, but will lose capacity quite rapidly thereafter. Or are you thinking of installing lower capacity deep discharge batteries?

I think I'm looking for lower capacity deep cycle alternatives. The weight is an issue as the main carer has difficulty lifting the OEM battery pack into & out of a car or lifting it to position it on the wheelchair bracket.

 

[TEO]

Those batts are probably considered to be 28ah (as they tend to use the C20, 20-hr value for classifying.... cos 28 is more than 20.
So a 19ah batt also rated at C20 is considerably less.
Something to be aware of.

I think you've hit upon the issue I'm having. I need to find a v basic explanation of the chart above with C values & ah so that I can make proper sense of your answer. Nothing to do with what you've said, just my level of understanding. I'll keep looking for the the right tutorial& then circle back to your answer, cheers

 

[TEO]

I assume the batteries are in series then? Otherwise you could just remove one to get the result your after

Yup exactly that the motors are 24v

 

[m_c]

Looking at the datasheet, the original batteries are ~6kg.
If you were to swap them for some LiFePo 20Ah, some preliminary searching puts the weight between 2.3 and 3kg, and can be had for around £95 each, without any real hit on performance.

 

[TEO]

Halving the battery capacity will likely more than half the run time, due to internal resistance and the batteries being worked relatively harder.

Are you trying to reduce replacement cost, or weight?

Ok, thanks, first part makes perfect sense.
As to the second; we can't go crazy buying really expensive batteries but the main priority is to reduce the weight so that the main carer can lift it.

 

[m_c]

I think you've hit upon the issue I'm having. I need to find a v basic explanation of the chart above with C values & ah so that I can make proper sense of your answer. Nothing to do with what you've said, just my level of understanding. I'll keep looking for the the right tutorial& then circle back to your answer, cheers

C rating is how the discharge/capacity test is done.
C1, means the battery is charged at the rated capacity for 1 hour i.e. for your 20Ah battery, it's discharged at 20A
C20, means it's discharged over 20h, at a rate of 1/20 the capacity, so for a 20Ah rating, would be discharged at 1A

The datasheet you posted is a good example of how different discharge rates affect the capacity.
The higher the discharge rate, the less capacity a battery will deliver, due to a combination of internal resistance and efficiency.

It's also worth noting, that in typical use, it's not recommended to use more than 50% of a lead acid batteries capacity.

 

[angellonewolf]

as a quick thing to cheak out of intrest have you removed one of the batterys and see if that makes there life a whole lot manageable ?


i know half the weight to you might seam better but is it ?

or as a chance is there a lighter weight unit around 2nd hand that might be better for the lighter side of it a look on facebook etc might help on that

 

[TEO]

Halving the battery capacity will likely more than half the run time, due to internal resistance and the batteries being worked relatively harder.

Are you trying to reduce replacement cost, or weight?

Ok, thanks, first part makes perfect sense.
As to the second; we can't go crazy buying really expensive batteries but the main priority is to reduce the weight so that the main carer can lift it

 

[TEO]

C rating is how the discharge/capacity test is done.
C1, means the battery is charged at the rated capacity for 1 hour i.e. for your 20Ah battery, it's discharged at 20A
C20, means it's discharged over 20h, at a rate of 1/20 the capacity, so for a 20Ah rating, would be discharged at 1A

The datasheet you posted is a good example of how different discharge rates affect the capacity.
The higher the discharge rate, the less capacity a battery will deliver, due to a combination of internal resistance and efficiency.

It's also worth noting, that in typical use, it's not recommended to use more than 50% of a lead acid batteries capacity.

Excellent, thank you.

 

[TEO]

as a quick thing to cheak out of intrest have you removed one of the batterys and see if that makes there life a whole lot manageable ?


i know half the weight to you might seam better but is it ?

or as a chance is there a lighter weight unit around 2nd hand that might be better for the lighter side of it a look on facebook etc might help on that

Tbh even half the weight may be too much as the carer has her own issues following polio as a child.
Other than spending way more than I have available I'm not seeing the perfect solution hence the question & casting around for good enough, really appreciate the help being given here & the thought people are putting into the op
These mobility aids run 12v in series to give 24v to the motors.
I'm keeping a sharp eye on fbm in the hope that something will turn up. Cheers

 

[TEO]

There is always the possibility that I'm looking at the whole issue in completely the wrong way.
Also that the issue will resolve itself in a natural way before I can find a solution but hey I really appreciate all the help being given & will pivot as necessary when circumstances change.
I'll try and explain the base issue more clearly in a new thread and that might well throw up better solutions. Cheers