Cobra Go Kart

[ian928]

This project have been at a standstill for loong, but now I have had some progress at last. I have come to the conclusion that I do not have time to do it like I really would like, so to get it finished I just need to put it together and get on with it. I had another thread on it but I get a message that it is closed, don't know why.

It is based on a Tonykart that I have chopped up to make narrower and longer. Up front are rims from a small ATV with integrated drum brakes. I replaced the bearings so they would fit the Tonykart spindles. Rear axle including rims are from a Wheel Horse mower. I have widened the 3/4" axle by welding 19mm bolts onto the ends of it. Rear axle is just strapped in place for alignment in the picture, I will widen the frame and place the bearings all the way out by the wheels.

I have a BOMA 1800W kit from Ebay that i plan to fit. I really would like a petrol engine, but electric is much less controversial if my kids are going to drive it on a parking lot etc.

Hope to get more progress soon!

 

[Denny]

Go gas with a cvt and don’t look back.

 

[Bansil]

What's up w/blue #1?

Downhill, mini cyclekart?

 

[ian928]

What's up w/blue #1?

Downhill, mini cyclekart?

Ahh, that was the first mini car for my boys, it is a pedal car converted with a transaxle from a mobility scooter and a speed controller off Ebay. I have widened the track and fitted wheels from a pram. My youngest son has driven it for many many hours!

I converted the electric "handbrake" system on the rear axle to a manual brake using a manual caliper bought on Ebay. The disc brake sits on the end of the motor so there is a danger of one wheel spinning backwards, they have however driven it on snow and ice and it brakes very good. It is fitted with a onboard 24V charger so my boys just needed to pull out the wire from underneath the hood when hey were done riding for the day. The fitted wheels had double the diameter of the mobility scooter so the top speed was about 3 times that of the mobility scooter, it was just the right speed for a 3+ Y. In fact they managed to get it onto 2 wheels once, so it was clearly fast enough. He could drive the whole day without running out of batteries.

When they grew they started to break the splines on the wheels and we decided to park it and build something bigger.

 

[Bansil]

Very check out mine , a bigger version

My kart build

All kinds of builds on this site

 

[ian928]

Very check out mine , a bigger version

My kart build

All kinds of builds on this site

That is beautiful workmanship! I look forward to follow the progress. I had never heard about the Vale before, wonderful special.

I remember seeing a homemade cyclecar in a private museum in England, it was built by a father to his son as a copy of his own racecar.

 

[Bansil]

Thank you Sir,

Sorry for thread hijack I am good at that

 

[ian928]

So, I have started thinking about batteries. I used 2 lead batteries in the small build, it worked very well so I thought about the same for this build. I see my local supplier has 18Ah batteries as the biggest. 4 of those will however be costly and heavy, 24kg! I can get a used/rebuilt 15Ah Li-ion battery pack for much less and the weight will be much lower. Can I use two battery packs in parallel? I would like to have a integrated charger as in the small car, I am not sure if this is possible with 1 or 2 Li-Ion battery packs? I hear about balanced charging without understanding what it means...

 

[Functional Artist]

So, I have started thinking about batteries. I used 2 lead batteries in the small build, it worked very well so I thought about the same for this build. I see my local supplier has 18Ah batteries as the biggest. 4 of those will however be costly and heavy, 24kg! I can get a used/rebuilt 15Ah Li-ion battery pack for much less and the weight will be much lower. Can I use two battery packs in parallel? I would like to have a integrated charger as in the small car, I am not sure if this is possible with 1 or 2 Li-Ion battery packs? I hear about balanced charging without understanding what it means...

First of all...those are some very kool lookin' karts

Used/rebuilt Li-ion batt packs
...Um...scary

Who knows what's in there
...how "used" are they
...how much capacity left in 'em (which is hard to tell without proper "equipment")
...are the cells "matched" (matching internal resistances)
...or "balanced" (all of the cells are the same voltage & capacities) & if so, how long will they stay that way?
...or even how well their assembled (welds, materials used etc.)

I'd stick with new batteries (lead or lithium)
...or at least "known" stuff like from electric cars & such (not "who knows")

I have used these batteries many times (~$30.00 ea.) 4 of 'em weigh ~40 lbs. (about the same as your average gasoline engine)
...with very good success (& very little danger)
...& get at least a 30 - 40 min "run time"
Mighty Max 12V 15AH F2 SLA Battery for Wagan 600 Amp - 4 Pack 730052496369 | eBay

 

[ian928]

Batteries: I did a search on Ebay and there are a lot of these: Chinese Li-ion

58Ah: Seems too good to be true...

This surprises me: "Maximum operating current: 13A" Is this correct? Seems very low, for 1800W I need 37,5A if I am correct. Compared to 600A from the battery pack Functional Artist refers to this seems strange. That is another thing, 48V 600A, that is 28KW through those connectors? What am I missing here? I am not very int electronics

 

[Functional Artist]

IMO those are for really light vehicles like electric bicycles & such

The "Maximum operating current: 13A" is determined by the "built in" BMS (battery management system)
...this is to help protect the cells from being over-discharged (like putting out 40A which is outside of their "specified operating parameters")
...or as the ad states, "Inside with protective circuit: overcharge, over discharge, over current, short circuit protection!"

Most lead batteries don't have a BMS so they can & will discharge "everything they got, captain" if asked (like ~600A)

W (watt) / V (voltage) - A (amperage)
...so, an 1,800W motor operated at 48V should need ~37.5A
...but, that's usually a peak rating (like taking off from a "dead stop" or like climbing a hill
...the average or constant amp draw, for this size motor, is usually much lower (like ~20A)

These motors, controllers, connectors & such were designed by (many different) professional engineers
...so, I'm pretty confident in the "use & safety" of them

 

[ian928]

So, I found another one, 58Ah, 50A continous: China battery, 2000W

Tempting... 58Ah and only 4 kg. It cost about the same as 4 SLA batteries with 12-15Ah.

How about this charger? Ebay Charger

On the small "Bugatti" car I mounted the charger onboard and connected it through the controller, I hope I can do the same here?

 

[Functional Artist]

It looks like it would work

Notice the difference between the (2) packs?

That first battery pack ("Maximum operating current: 13A") is built with 39 of the 18650 cells (13S3P)
...where as the second battery pack (Maximum continuous discharge current 50A) has 78 of the 18650 cells, in a (13S6P) configuration

As for a charger for the "second" battery I'd say something like this should work
54.6V 2A Li-ion Battery Charger Adapter For 48V Battery Ebike Electric E-Bike | eBay
...but, it is only a 2.5A charger so it will take a while to charge

* Keep in mind that for a battery pack, made out of 18650 cells, that have a nominal voltage of 3.7V per cell
...has a low voltage or "cut off" of ~3.15V per cell (13S x 3.15V - 41V)
...& a max voltage or "top charge" of ~4.2V per cell (13S x 4.2 = 54.6V)

This type of a battery pack has a "dedicated" input (for charging) & out put (dis-charging)
The yellow plug (with big ~10g. wires) is the dis-charge connector
...& the black plug (with smaller, probably ~18g. wires) is the charging port

So, if you can, just mount that charge plug/port somewhere accessible
...or even just make it so it's "grabbable" to easily plug in

IMO This set up" is kind of a plus
...because, if you have a "main cut off switch"
...the entire kart can be "shut off" while charging
This way, no one can accidentally drive off with the battery charger still attached

 

[ian928]

Thank you Functional Artist, your assistance is much appreciated!

What is the difference between the charger you Linked to, other than it being 2,5A whereas the one I Linked to was 5A? I think the battery has Aviation style connector.

Also, do I understand you correct with «not being able to drive off with the charger attached» meaning that the battery will not provide power out when being charged?

 

[Functional Artist]

When I "click" on the link above I go to
https://www.ebay.com/itm/3841844184...rentrq:bfa802e817b0a0f0fe2ab751fff6d866|iid:1

...which looks to be a battery & charger
...but, I don't see where it's a 5A charger either

The most important specification (for charging) for this type of battery is max voltage or "top charge" of ~4.2V per cell (13S x 4.2 = 54.6V)

"Not being able to drive off while attached to the charger" refers to
...your battery cut-off switch (if equipped with one) being turned "off" while charging (so the batt pack is totally (electrically)separated from the kart)
...or even having the batt pack being simply "un plugged" will do

 

[ian928]

I think you are looking at the first battery i Linked to! Check out the one named 2000W!