My kids ride on Jeep project

[Weldingtutor]

I have come across an old 24 Volt mobility scooter and my plan is to take the running gear out of it and build it into a jeep for kids. The 2x 12 Volt deep cycle lead acid batteries are too old and are no longer holding charge.
I have 2x Volkswagen E-Golf batteries these are 14.4 Volt each I have removed the computer circuit boards on them making them just straight-out batteries.
The plan is to use these two batteries in series to give me the 24 Volt needed to drive the mobility scooter running gear, But I need to step down the voltage from 14.4 Volt to 12 Volt on the individual batteries or 28.8 Volt to 24 Volts off both batteries what is the best way of doing this?
Mobility scooter motor is 24 Volt and 5 Amps. The batteries are 14.4 Volts and **** loads of Amps Sorry; “I do not know the Amp output capacity.”

 

[ZipZapOuch]

It's very unlikely that the designer specified everything so tightly in the 24v mobility scooter that it cannot handle 29v from the lead-acid batteries.

The cold-cranking amps is the maximum amperage that the battery can deliver to a load (depends on the resistance of the load attached to the battery). The motor amperage is the current draw at 24v supply.

Also, make sure the batteries on the scooter are really connected in series. Some are in parallel just to last longer (more range) at 12v.

 

[rjenkinsgb]

I have 2x Volkswagen E-Golf batteries these are 14.4 Volt each I have removed the computer circuit boards on them making them just straight-out batteries.

Those batteries have series-connected lithium cells, four per module (and 3? parallel chains. internally).
That puts the full charge voltage at around 16.8V

A normal "12V" lead-acid battery has a full charge voltage of ~15V on charge, so not much in it.

The voltage itself would not be a problem.

But: You cannot substitute lithium cells/batteries for other types, without also ensuring ALL the correct balance, monitoring and charge voltage control functions are included for safety!

Lithium cells contain equivalent energy to around 1/3rd their weight of TNT - do you want your kids sitting on or near that, if the cells could fail due to lack of proper safety and monitoring circuits?



I cannot find all that much in the way of technical info on those E-Golf batteries, other than mention that the BMS (battery management system) is external. See the link below.

Any series-cell lithium batteries MUST have cell balance (which keeps each cell in the series chain at the same charge state) and absolutely spot-on correct charging voltage control, otherwise the cells can burst or catch fire! They must also have under- and over-voltage protection on a per-cell basis.

The batteries look to have several connectors, which are probably the balance and monitoring points for the BMS?

You mention that you removed the "computer boards" - they were likely part of the cell monitoring, though from what I can see the whole battery set is part of a CAN management network, so not easy to re-use with complex electronics.

Some info on the e-golf batteries here:

E Golf Battery pack - openinverter forum

 

[ZipZapOuch]

do you want your kids sitting on or near that, if the cells could fail due to lack of proper safety and monitoring circuits?

This is the most importantly point!

I would not be so confident of my electronics skills or fabrication skills or ability to select proper materials. I include fabrication and materials selection because minor things like that make a difference in a moving vehicle where you have vibrations (movement of wires) and thermal cycling and rain (possible wire abrasion / possible cracking of solder joints / possible shorting from contaminated rain water (even sprinkler water). Also, watch the link below in case there is a crush or rupture or even overcharging possibility (overcharging also means unbalancing of series-connected cells)

Overly discharging and charging unbalanced cells can lead to damaged battery packs.

I wouldn't put my kid in my own kart without extensive testing (more than just a few charge discharge cycles ). I'm not a fan of lithium batteries in diy projects.

Good catch rjenkinsgb , not a safe place for kids.

 

[Weldingtutor]

I am so glad that I posted my intentions before going ahead and fabricating a kids jeep
“THANKYOU SO MUCH”.
Your comments were an immense help.
I did not understand, and I just didn’t know what I didn’t know.
My plan was to run the batteries until discharged, then recharged them to 14.4volts, run them again, recharge, over and over and over but it sounds like I would be priming bomb for detonation.

 

[Weldingtutor]

By the way, if anyone interested this is what the batteries look like with the covers off and the circuit boards unscrewed

 

[ZipZapOuch]

The next question is where/how to dispose it without setting the garbage truck or landfill ablaze.

 

[Weldingtutor]

Now that is a very good question

 

[rjenkinsgb]

Put them on ebay, with the circuit boards etc., as they are quite popular with EV builders & repairers, from what I can see.

 

[ZipZapOuch]

Now that is a very good question

all lithium batteries banned from air shipments - slow boat only if they leave your island. Even little CR2032 batteries can only be shipped by air if they are on a carryon.

 

[Nigel Goodwin]

The next question is where/how to dispose it without setting the garbage truck or landfill ablaze.

Just take them to your local recycling centre.

 

[rjenkinsgb]

Now that is a very good question

What country are you in?

 

[Pommie]

I had some lithium rechargeable batteries which I needed to dispose of. I hit them with a big lump hammer and when the fireworks stopped I threw them in the local river (Brisbane). They do have recycle bins in some supermarkets here but they only take "normal" batteries - D,C,AA,AAA PP3 etc.

Mike.

 

[Nigel Goodwin]

I had some lithium rechargeable batteries which I needed to dispose of. I hit them with a big lump hammer and when the fireworks stopped I threw them in the local river (Brisbane). They do have recycle bins in some supermarkets here but they only take "normal" batteries - D,C,AA,AAA PP3 etc.

Mike.

Don't you have recycling centres there?.

 

[Pommie]

Don't you have recycling centres there?.

Incredibly, they do but they don't take lithium batteries.

Mike.
BTW, the battery involved was a flat type out of a tablet so hitting with a lump hammer completely destroyed it.
Edit, there have been a few tower fires here due to people throwing away CR2032 type batteries and the compactor (at the bottom of the rubbish chute) crushing them. Big problem nobody seems to have a solution to.