wich buck converter do i need for quickie 6000z electric wheelchair?

[electrolover]

HI i have a quickie 6000z and i have no battry for them. I just build a lip 13s4p 48volt battery3,7 nominal (54.6v once charged)
i would like to use this lipo battery to power my wheel chair so someone told me to buy a dc dc buck converter.

i need help cause i did contact a chinese guy on aliexpress and he said he can build one for me and asked me to send him info.

I talked to a wheelchair expert and he told me that this wheel chair works at 25 26 volt . minimum working volt being23 and max 26. it told me the amp is between 10 -20 range.

1 now do i need other information?
2 in a regular battery, the more energy is spent the more the voltage drops for esxample gel batt maybe 26v full and after 3 hours of rodad usage they have dropped to 24 v maybe. With a buck converter, 48 to 24 volt for example is the out put current always 24 v or it will also drop as energy is spent ?
tx

 

[rjenkinsgb]

You are being misled, 23-26V is nonsense for a lead-acid system.

A lead-acid 12V battery has a range of 15V full charge to 11V discharged.
So, a working range of at least 30V - 22V for a 24V system.

Why not just rearrange the battery to 7S (and any number parallel) ??

As long as the battery voltage roughly fits within that 22 - 30V range, it's in the design spec of the wheelchair drive system and will be a lot more efficient than running via a DC-DC converter.


Make sure you allow for balance charging on a series lithium pack, not just under/over voltage protection!

 

[Pommie]

I agree, rewire as 7s. What capacity/size are your cells?

Mike.

 

[electrolover]

3,7 nominal 4,2 charged full . i have a 13s 4p Sony US18650 VTC4 (LiMn 2100 mAh,

Any one knows the exact voltage that electric wheelchair use? from what i remember it is something like 23,5 to 25,9v

 

[Pommie]

If you rewire as 7s8p (4 more cells needed) then you'll have a (theoretical) capacity of around 16Ah which will give you between 0.5 and 1.5 hours run time.

Mike.
Edit, why did you go with 13s4p?

 

[electrolover]

the thing is the voltage that bothers me 7s means 25.9 to 29.4v how to find out what is hte maximal voltage that the wheelchair can use ?

the initial 13s is for 48 v motor on something else

 

[Nigel Goodwin]

the thing is the voltage that bothers me 7s means 25.9 to 29.4v how to find out what is hte maximal voltage that the wheelchair can use ?

It's unlikely to be of any concern, a motor can accept a huge range of voltages - if you apply a slightly higher than usual voltage at full speed, then it will simply go a bit faster

So there's no 'exact' voltage - your wheelchair 'expert' sounds like he knows little or nothing about electronics, and is just making things up.

As already mentioned, the original lead acid batteries ranged from 22V to 30V depending on how charged they were.

 

[rjenkinsgb]

The original batteries for that wheelchair are two, 12V deep-discharge gel electrolyte lead-acid types, according to the information I can see on the manufacturers web site spares list.
(At ludicrous prices - around $500...)

The acceptable working voltage range of the wheelchair is therefore the same as the voltage range of 2 x 12V lead-acid batteries in series.

That varies from 30V while on charge and near 100% charge, down to 22V or less on load and near total discharge.

Seven lithium cells in series fit nicely in that range; around 3V per cell when near total discharge (21V) and 4.2V per cell at full charge (29.4V).

 

[audioguru]

Be careful. A Lithium battery has less weight than a lead-acid battery so the wheelchair might tip over if you corner too fast. Do a wheelie?