Help picking batteries

[Needshelp]

Hey everyone, im building my own cart and was planning on running a 3000watt, 72volt motor. what would be ideal batteries to use to get a run time of at least 20 minutes?

Most batteries have around 4ah or so but with the motor pulling 41amps (3000watt/72volts=41amps) that would only be around 5 minutes (4ah/41amps= .098 or 5 minutes or so) of drive time. I hope im doing the math wrong, but if I'm not is there any reccommedations?

 

[EpsilonZero]

You could roll the dice with an ebay battery pack, make your own by combining reputable RC packs (common tactic), or build a battery from individual cells. The actual performance of the battery is increasingly less of a mystery in that order. Used EV battery modules are also an option.

The motor will pull more than 41 battery amps under acceleration but far less while cruising. Your power requirements will be dictated mostly by weight, terrain, and driving style. Personally, I like to see triple the continuous rating of the motor for short bursts at least. Keep in mind that your pack will have more usable energy the less you stress it (you will notice stress with lots of voltage sag) and the full Ah of a battery is not actually available because you have to stop discharging at maybe 80% depth of discharge (depending on chemistry).

What frame, motor, controller, tires, and gearing are you using?

 

[Needshelp]

You could roll the dice with an ebay battery pack, make your own by combining reputable RC packs (common tactic), or build a battery from individual cells. The actual performance of the battery is increasingly less of a mystery in that order. Used EV battery modules are also an option.

The motor will pull more than 41 battery amps under acceleration but far less while cruising. Your power requirements will be dictated mostly by weight, terrain, and driving style. Personally, I like to see triple the continuous rating of the motor for short bursts at least. Keep in mind that your pack will have more usable energy the less you stress it (you will notice stress with lots of voltage sag) and the full Ah of a battery is not actually available because you have to stop discharging at maybe 80% depth of discharge (depending on chemistry).

What frame, motor, controller, tires, and gearing are you using?

Hey thanks for the reply! Its actually a drift trike im building. Im using one of those pedal Razor drift trike and welding some tubes to mount the motor and batteries. Im using just a generic motor, controller, combination from ebay. I planned on running a 20tooth sprocket on the motor and a 52tooth sprocket on the axle.

I made the choice to abandon the 3000 watt motor for a 1800watt 48volt motor to help me with my battery situation and its cheaper so thats always good.

So RC cars can do the trick? I would need to research this as I have not come across that.

 

[EpsilonZero]

You should be aware that a lot of those generic controllers have a soft start to them that may or may not be able to be bypassed in janky ways and you are going to want maximum torque immediately in a drift trike. That being said, you will need a very different gear ratio. Get the smallest motor sprocket you can and the largest axle sprocket that will fit. I wouldn't go for a lower rated motor if I were you; You're going to want the power. The RC packs I am referencing are the type you can find at HobbyKing online.

 

[Needshelp]

You should be aware that a lot of those generic controllers have a soft start to them that may or may not be able to be bypassed in janky ways and you are going to want maximum torque immediately in a drift trike. That being said, you will need a very different gear ratio. Get the smallest motor sprocket you can and the largest axle sprocket that will fit. I wouldn't go for a lower rated motor if I were you; You're going to want the power. The RC packs I am referencing are the type you can find at HobbyKing online.

Should I just keep the 12 tooth sprocket that comes with the motor?

what should I be looking for in the batteries? I know I need 72 volts, but what about the “ah” as I am concerned with the amount of time i get to play with it. I dont want the juice to run out after 5-10 minutes...

 

[KMEFA]

You would want to get the 10t - #35 chain double ''D'' motor sprocket, off e-bay ect., ''for those motors''.

That's the smallest #35 motor sprocket I have found so far...

I ''wouldn't'' run the stock motor sprocket / #25 chain size.

I would go with a split sprocket hub though, & probably start off with around 75t - #35split sprockets.

That would give you a starting ratio of 7.5 - 1, & be plenty stout.

You would also want to add some kind of chain /sprocket guard ect.,, as that big sprocket will probably be ''very'' close to the ground.

I

 

[KMEFA]

Should I just keep the 12 tooth sprocket that comes with the motor?

what should I be looking for in the batteries? I know I need 72 volts, but what about the “ah” as I am concerned with the amount of time i get to play with it. I dont want the juice to run out after 5-10 minutes...

Higher ah = longer run time ect.

If a battery says 10ah, that means the battery theoretically can pull 10 amps constant for 1 hr. on a charge.
I wire my packs parallel, so each added pack multiplies the ah.
So 2 packs @ 10ah ea. wired in parallel,, now gives you a capacity of 20 ah.
Which means now also,, ''if say'' your motor is pulling 20 amps constant,, you should be able to get close to an hr. run time,, if they are good quality batteries,, & actually are as advertised.

Regardless,, I would get the highest ah batteries you can find.

Be careful though,,
Packs on e - bay ect., like the ones that say 58000ah ect, are ''definitely not''.

You want to look for packs that have ''realistic'' advertised ratings like 10, 12,14ah,, ect.

 

[Needshelp]

Thanks guys this is a great help to me.

any recommendations on the battery pack to buy?

already bought my 10t and 72t sprocket!!!!

 

[Needshelp]

Higher ah = longer run time ect.

If a battery says 10ah, that means the battery theoretically can pull 10 amps constant for 1 hr. on a charge.
I wire my packs parallel, so each added pack multiplies the ah.
So 2 packs @ 10ah ea. wired in parallel,, now gives you a capacity of 20 ah.
Which means now also,, ''if say'' your motor is pulling 20 amps constant,, you should be able to get close to an hr. run time,, if they are good quality batteries,, & actually are as advertised.

Regardless,, I would get the highest ah batteries you can find.

Be careful though,,
Packs on e - bay ect., like the ones that say 58000ah ect, are ''definitely not''.

You want to look for packs that have ''realistic'' advertised ratings like 10, 12,14ah,, ect.

But if they are wired in parrallel you cant add up the voltage right? Only the ah?

so i would have to find a 72v with a high ah? Or am i completely wrong?

 

[EpsilonZero]

But if they are wired in parrallel you cant add up the voltage right? Only the ah?

so i would have to find a 72v with a high ah? Or am i completely wrong?

Parallel increases amp-hours, series increases voltage. You can wire batteries both series and parallel in the same pack (e.g., 12s4p). So, if you had four 36v 10Ah batteries, you could wire them in 2s2p for 72v 20Ah. You increase total pack power (Wh or watt-hours) whether you increase voltage or Ah, but you want to have a good voltage match between the batteries, controller, and motor.

Make sure you're using the same chemistry, Ah, and voltage of batteries when doing this.

 

[inchtime]

I'm just picking this thread up again as I am embarking on a similar project and would love some advice picking the right batteries.

I am buying a 72V 3000W electric motor (MY1020 as often seen on eBay) to build an electric go kart in a school workshop with some students.

I understand wiring the batteries in series or parallel to raise either voltage or amp hours. As buying a suitable 72V lithium battery (or even making my own out of 18650 batteries) is out of my budget I am going to run 6 x 12V lead acid batteries (as seen on typical scooters/cars) in series. I thought 20 - 30ah would be a good starting point - The motor runs on 42amps so that would hopefully give 30mins run time or more if it wasn't on full power the whole time. I get the points above on how much the motor might draw depending on the strain it is under.

My question is this - what type of lead 12v vehicle battery should I look at to run in series? Here are my thoughts/uncertainties:

- I think it would be better to get a sealed "AMG" or "gel" - for safety reasons of kids using it.

- I don't think I need to be concerned about a high CCA on the battery as I'm not starting a motor in the same way as diesel/petrol car. Although the motor may pull more than 42 amps I don't think it's supposed to go over 78amp. A higher of CCA (eg. 330A) doesn't matter so much? I was originally thinking of getting 6 Yuasa Active Garden batteries but now I'm not so sure (especially as they're quite big an heavy).

- If CCA is not a concern - would a "deep cycle" battery be a better option? I think they are OK with loosing more power than "starter batteries" but I'm not sure if that is applicable if I'm continuously drawing something like 42amps.

- Parallel is not an option for this set up as the Lead batteries are quite bulky anyway.

I have more questions on the best options to charge such a battery bank but I'll leave that for another post! Any advice would be much appreciated!

 

[EpsilonZero]

I'm just picking this thread up again as I am embarking on a similar project and would love some advice picking the right batteries.

I am buying a 72V 3000W electric motor (MY1020 as often seen on eBay) to build an electric go kart in a school workshop with some students.

I understand wiring the batteries in series or parallel to raise either voltage or amp hours. As buying a suitable 72V lithium battery (or even making my own out of 18650 batteries) is out of my budget I am going to run 6 x 12V lead acid batteries (as seen on typical scooters/cars) in series. I thought 20 - 30ah would be a good starting point - The motor runs on 42amps so that would hopefully give 30mins run time or more if it wasn't on full power the whole time. I get the points above on how much the motor might draw depending on the strain it is under.

My question is this - what type of lead 12v vehicle battery should I look at to run in series? Here are my thoughts/uncertainties:

- I think it would be better to get a sealed "AMG" or "gel" - for safety reasons of kids using it.

- I don't think I need to be concerned about a high CCA on the battery as I'm not starting a motor in the same way as diesel/petrol car. Although the motor may pull more than 42 amps I don't think it's supposed to go over 78amp. A higher of CCA (eg. 330A) doesn't matter so much? I was originally thinking of getting 6 Yuasa Active Garden batteries but now I'm not so sure (especially as they're quite big an heavy).

- If CCA is not a concern - would a "deep cycle" battery be a better option? I think they are OK with loosing more power than "starter batteries" but I'm not sure if that is applicable if I'm continuously drawing something like 42amps.

- Parallel is not an option for this set up as the Lead batteries are quite bulky anyway.

I have more questions on the best options to charge such a battery bank but I'll leave that for another post! Any advice would be much appreciated!

I would not advise lead acid batteries, but you need to use SLA deep cycle if you do use them. You're talking about like 150lbs and several hundred dollars for batteries that can only be discharged 50% and have relatively few charge cycles. SLA is best for small toys that won't be used long like a 6v ride-on that comes with an SLA. Why not get some hobby batteries like https://hobbyking.com/en_us/turnigy-heavy-duty-5000mah-7s-60c-lipo-pack-w-xt90.html?

 

[Functional Artist]

IMO a 48V set up would be more cost efficient, simpler & safer, for a student project.

Either way, I'd just use 12V 15AH SLA (sealed lead acid) batteries ~10 lbs. ea. & ~$25.00 ea.

As far as run time, if your kart isn't super heavy or has really large wheels, you should get at least 30 min+ of "run time" using SLA's

For more info, check out the Damien thread.
This kart has a 48V 1,800W motor but, alot of the concepts still apply
(5) Damien | DIY Go Karts

 

[KMEFA]

I would not advise lead acid batteries, but you need to use SLA deep cycle if you do use them. You're talking about like 150lbs and several hundred dollars for batteries that can only be discharged 50% and have relatively few charge cycles. SLA is best for small toys that won't be used long like a 6v ride-on that comes with an SLA. Why not get some hobby batteries like https://hobbyking.com/en_us/turnigy-heavy-duty-5000mah-7s-60c-lipo-pack-w-xt90.html?

SLA batteries are boat anchors, & like Epsilon Zero was pointing out,, SLA's are ''not'' really for ''repetitive'' ''high'' discharges.
That's why jump packs with SLA's , don't hold full charge capacity for very long,, & just get worse & worse. …
I think you would be throwing money away,, plus ''a lot'' of dead weight that you don't need.
Also running them in series with that 72v. set up,, you would drain/ruin them ''real'' quick.

Personally, I run Li packs that have BMS protection circuity integrated in them,, with using XT-90 anti spark connectors.

Like Functional Artist said,, a 48v set up is more practical & safer.

A 48v 2000w BM 1109 set up is what I run on my Kart, & does surprisingly well.
That set up with a 12 fet controller & Hall pedal, is only around $130 bucks.
You can get 13s - 4p - 48v packs with BMS for around 100 bucks ea. & run them parallel.
2 of those 48v packs, depending on ''actual'' capacity,, would probably give you your 30min. run time,, depending also on gearing, total gross weight with driver,, & throttle management.

I have been running misc. 36 & 48v Li packs with BMS, in various applications for over 3 years now,, & haven't had any troubles what so ever.



Maybe also look into hard case Lithium motorcycle batteries ??
They weigh ''tons'' less than SLA's & gels,, & are pretty safe.

My 2 cents.

I

 

[inchtime]

I would not advise lead acid batteries, but you need to use SLA deep cycle if you do use them. You're talking about like 150lbs and several hundred dollars for batteries that can only be discharged 50% and have relatively few charge cycles. SLA is best for small toys that won't be used long like a 6v ride-on that comes with an SLA. Why not get some hobby batteries like https://hobbyking.com/en_us/turnigy-heavy-duty-5000mah-7s-60c-lipo-pack-w-xt90.html?

Thanks EpsilonZero. I was looking at SLA because of the cost of lipo but I'm just checking hobby king again. If I took your example or say this 4S one, I could put 5 in series. But am I not right in thinking I would need to add another row in parallel to take it up to at least 10ah instead of 5? Otherwise it wouldn't run for very long...?

Is it better to put together a 10ah hobbyking lipo (5 x 4s example above, 2 sets in parallel) or 6 x 20ah SLA - if weight and size were not factors? (ie. if SLA are only good for 50% discharge).

 

[inchtime]

SLA batteries are boat anchors, & like Epsilon Zero was pointing out,, SLA's are ''not'' really for ''repetitive'' ''high'' discharges.
That's why jump packs with SLA's , don't hold full charge capacity for very long,, & just get worse & worse. …
I think you would be throwing away,, plus ''a lot'' of dead weight that you don't need.
Also running them in series with that 72v. set up,, you would drain/ruin them ''real'' quick.

Personally, I run Li packs that have BMS protection circuity integrated in them,, with using XT-90 anti spark connectors.

Maybe look into hard case Lithium motorcycle batteries .
They weigh ''tons'' less than SLA's & gels,, & are pretty safe.

I

Thanks 174. I would much prefer a Li pack. They're just so expensive - maybe double the cost. I even thought about making my own with 18650.

Definitely going to use the XT-90 spark connectors. They look good.

 

[KMEFA]

Thanks 174. I would much prefer a Li pack. They're just so expensive - maybe double the cost. I even thought about making my own with 18650.

Definitely going to use the XT-90 spark connectors. They look good.

I just added on my above post,, check it out .

Also,,
Just noticed that you are in the UK.
Not sure on current protocol of getting Li packs ect...
I was chatting with someone from the UK on another forum awhile back about this,, & he told me that it's difficult & expensive getting that stuff there.

 

[Functional Artist]

IMO lithium batteries are NOT best suited for beginners that are just learning about DC motors/electronics
...they are for "stepping it up a notch" & more advanced builds

FYI:
On the Excalibur kart, I got well over 45 min of "run time" using (4) 12V 15AH SLA batteries, powering (1) 48v 1,000 MY-1020 motor
...& a little over 30 min "run time" when they were powering (2) 48V 1,000W motors

* Yes, I got (3) times more "run time" when running the lithium battery
...but, it cost (3) times more
...& it couldn't handle powering the (2) motors
...but, the SLA's could

(3) 2020 - Excalibur Electric Racing kart | DIY Go Karts

 

[KMEFA]

IMO lithium batteries are NOT best suited for beginners that are just learning about DC motors/electronics
...they are for "stepping it up a notch" & more advanced builds

FYI:
On the Excalibur kart, I got well over 45 min of "run time" using (4) 12V 15AH SLA batteries, powering (1) 48v 1,000 MY-1020 motor
...& a little over 30 min "run time" when they were powering (2) 48V 1,000W motors

* Yes, I got (3) times more "run time" when running the lithium battery
...but, it cost (3) times more
...& it couldn't handle powering the (2) motors
...but, the SLA's could

(3) 2020 - Excalibur Electric Racing kart | DIY Go Karts

Am just curious,, have you looked into those lithium hard case motorcycle batteries ??

 

[Functional Artist]

There's tons of stuff "out there" which ones are you referring to?
...please post a link