Help picking batteries

[KMEFA]

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

Pretty much in general,, I haven't checked them out lately.

 

[EpsilonZero]

* 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

That's an issue with a lot of the lithium from random Chinese resellers. You don't always know if you're getting the proper capacity or discharge characteristics. Lithium chemistries definitely can support high drain in the proper configuration. They are also lighter and, I would argue, less expensive overall. You don't have to continuously replace them!

My kart...

A kart with hobby lipos...

 

[inchtime]

Thanks 174. I've been reading your post again and searching for 36V packs to cost them up. As far as I can see it works out at least twice as costly (but maybe that's just here in the UK!) using lithium packs. I going to price up the alternatives to see if my school will buy them!

So i think my options could be:
- hobbyking (5 x 4S lipo pack 5ah) x 3P - giving me 15ah. Around £560. Plus a charger and BMS (not that I know anything about BMS yet). If I want 20ah I'm looking at £740.
- (36v 10ah battery pack x 2) x 2 parallel. Comes out expensive and it's less clear on some of these if they're OK with running 42amps continually.
- 72v 20ah pack on ebay - less information here on the specifics. Around the £600 mark.
- SLA batteries. Cost effective but big and heavy and not really the way to do it.

The thing about this school project is that we'll be spending loads of time over 3 days making it and very little time running it! After we've run the kart for 30 minutes we'll probably disassemble it for a year. (we have 4 teams make go petrol karts over 3 days - 10 students per team. I want us to make an electric one this year!

 

[EpsilonZero]

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).

I would definitely parallel the packs to get more run time. As far as I am concerned, SLA is dead to me at this point. They are heavy, expensive, contain comparatively little power and turn into e-waste quickly. All that weight is creating the need to expend even more energy to move them and puts more strain on all components. This weight will dramatically alter handling characteristics and slow acceleration as you get into higher voltages. Ironically, as the higher voltage allows an appropriate motor to spin faster the high weight eats at the torque you need to get it there.

 

[EpsilonZero]

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

I have. Do you know of a good reseller?

 

[EpsilonZero]

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

Well, I think it is time for you to switch to Lithium. You're designing and building your own frames. You've worked with larger motors too. How about a dual ME1305 kart powered by a couple of Zero motorcycle batteries?

 

[inchtime]

I would definitely parallel the packs to get more run time. As far as I am concerned, SLA is dead to me at this point. They are heavy, expensive, contain comparatively little power and turn into e-waste quickly. All that weight is creating the need to expend even more energy to move them and puts more strain on all components. This weight will dramatically alter handling characteristics and slow acceleration as you get into higher voltages. Ironically, as the higher voltage allows an appropriate motor to spin faster the high weight eats at the torque you need to get it there.

Thanks EpsilonZero. And it looks like my manager is happy for me to invest in the lithium packs instead of SLA which is great. So now I probably needs some advice on which hobbyking battery packs to build the bank. Would this be a good option.

4s x 5 in series to get to 72V (5ah) - Hobbyking link
3 sets in parallel to bring it up to 15ah.
That's 15 packs in total.

How best do I charge them? I believe I need a need a BMS also but I'm not sure how to approach all that.

 

[KMEFA]

I have. Do you know of a good reseller?

No, I haven't checked out those Lithium hard case motorcycle batts. lately.
Was just wondering if you Guys have maybe been checking them out.

 

[Functional Artist]

Well, I think it is time for you to switch to Lithium. You're designing and building your own frames. You've worked with larger motors too. How about a dual ME1305 kart powered by a couple of Zero motorcycle batteries?

Yup, I have been venturing into lithium, (very cautiously) & only after years of learning & research

I just don't think it's a good idea for beginners (folks who "don't have a clue") to be playing with them.

They have enough to try-n-figure out/understand the "mechanics" of a go kart that's motivated by an electric motor & powered by a battery
& then, getting everything bolted together & wired up

Before they have to worry about spending "big money" on batteries that
...that they may only use a few times (project over, lose interest etc.)
...that are really expensive (compared to available options)
...that could explode (if overcharged)
...or become useless (if over discharged)
...& BMS's (battery management systems)

Then, if they want to go faster or farther then, Yup advance/step up to Lithium power
...again, just my opinion

* I just upgraded Elmoto to (2) of the 48V 50Ah Chevy Volt modules (in parallel) to double my range
...Hmmm, I need to update the thread

 

[KMEFA]

Thanks EpsilonZero. And it looks like my manager is happy for me to invest in the lithium packs instead of SLA which is great. So now I probably needs some advice on which hobbyking battery packs to build the bank. Would this be a good option.

4s x 5 in series to get to 72V (5ah) - Hobbyking link
3 sets in parallel to bring it up to 15ah.
That's 15 packs in total.

How best do I charge them? I believe I need a need a BMS also but I'm not sure how to approach all that.

15 of those packs is going to be some pretty good coin.

I would seriously consider shelving ect. that 72v set up for now,, & going with the 48v - BM 1109, 1800- 2000w BLDC combo instead,, & running 2 - 48v 13s - 4p packs in parallel, with ea. pack having BMS, & at least 10ah of ''true'' capacity.
Those 2 in parallel should give you at least 20ah, & your 1/2 hr run time,, like I posted before.
Other than making up a parallel harness & soldering connectors also,, that combo is pretty much ''PNP'' - plug n play.

Am also a big electric R/C Guy of ''many'' years,, & what I have seen ''a lot'' with HK Lithium's of various sorts,, some of it has been just about down right scary,, especially if they get over discharged.
Have even seen them catch fire more than once,, & the Lipo's will also burn under water.
You set one off, the others are soon to follow,, especially if they are all stacked next to ea. other.

Rumor has it that Lipo's might have taken out that Malaysia flight,, as some sources are saying that the cargo hold had multiple crates of ''fresh''' ones in it.
I also read that Lipo's are the most volatile within the first 48hrs. that they are manufactured.



Going with 2 ''or more'' 18650 packs with built in BMS, would be the ''way'' safer option.
Probably cheaper too.
Messing around with 15 of those HK packs, is just asking for trouble, IMHO.

 

[inchtime]

Thanks 174. Its good advice. I'll definitely look at lithium-ion again with the 18650 packs as alternative to the HK packs.

And definitely food for thought from you too Functional Artist. I am on a learning curve with batteries and the SLA batteries would definitely be the easier/cheaper option!

So three different types of battery recommended - all for good reasons!

"174" - I have one motor already on the way which is a 72V-3000W but they say it can run at 48V also. The price difference wasn't too much between the 48V-2000W and 72V-3000W motor. I'm not sure whether mine will still run at 3000W if I just put 48v into it (ie. draw a higher current). Doubt it. The combo option sounds fun ...so maybe I can try this next year if we get another motor.

 

[KMEFA]

Thanks 174. Its good advice. I'll definitely look at lithium-ion again with the 18650 packs as alternative to the HK packs.

And definitely food for thought from you too Functional Artist. I am on a learning curve with batteries and the SLA batteries would definitely be the easier/cheaper option!

So three different types of battery recommended - all for good reasons!

"174" - I have one motor already on the way which is a 72V-3000W but they say it can run at 48V also. The price difference wasn't too much between the 48V-2000W and 72V-3000W motor. I'm not sure whether mine will still run at 3000W if I just put 48v into it (ie. draw a higher current). Doubt it. The combo option sounds fun ...so maybe I can try this next year if we get another motor.

As long as the controller you come up with will work with that motor at those lower voltages & not cut off,, you should be fine.
There is various ''semi'' self learning controllers out there.

 

[EpsilonZero]

Thanks 174. Its good advice. I'll definitely look at lithium-ion again with the 18650 packs as alternative to the HK packs.

And definitely food for thought from you too Functional Artist. I am on a learning curve with batteries and the SLA batteries would definitely be the easier/cheaper option!

So three different types of battery recommended - all for good reasons!

"174" - I have one motor already on the way which is a 72V-3000W but they say it can run at 48V also. The price difference wasn't too much between the 48V-2000W and 72V-3000W motor. I'm not sure whether mine will still run at 3000W if I just put 48v into it (ie. draw a higher current). Doubt it. The combo option sounds fun ...so maybe I can try this next year if we get another motor.

We didn't talk about repurposed EV batteries yet. FA and I both have vehicles powered by variations of Chevy Volt battery modules, for instance. Nissan Leaf modules are popular also, though seem to be more rare now. These batteries are less prone to fire and explosion and are well engineered (newer Leaf modules at least...). With the LiPo packs, you could just use a hobby charger on them individually to save time and money.

Motors can be run at lower or higher voltages (within reason) if the controller can handle the battery pack voltage and the motor rpm is constrained so it doesn't melt or just fly apart.

The lower pack voltage supplied to your 72v motor will mean that your max rpm is reduced significantly. More current won't raise the rpm, though the motor will use up to whatever the controller can feed it under enough load. It isn't advisable to intentionally provide current beyond the motor's rating since more current means more heat which means more resistance and even more heat and then electrical burning smells and magic smoke.

 

[KMEFA]

Just general heads up info on playing with Lipo's,, for anyone interested...

You ''always'' want to ''balance'' charge & discharge them, with a decent ''upper hobby grade'' balance charger/ discharger ect.

Balance charging,, you want to charge them at a current rating of around 10% lower than the ''Ma'' capacity of the packs.

Balance discharging & ''storage'',, you want to have your cut off @ around 10% above the nominal voltage of the pack.
I always balance discharge/ storage,, @ 50% less current rating of ''Ma'' capacity of the packs.

You ''never'' want to run the pack down below nominal voltage, ''with checking @ rest''.

Safe cut off running with any Lipo,, should be at least 5% above nominal voltage.

A fully charged Lipo should be used within a day or so,, & don't leave it fully charged for more than a couple of days.


I have Lipo's of ''many'' various sorts that are still working like new, & not puffed at all,, even after 10 - 12 years,, because I follow these steps.

If a pack swells/ puffs on you,, it needs the ''power'' leads cut off, & then safely discarded., ASAP.

I

 

[KMEFA]

Guess no body gives a $hit about me spending time as a courtesy on wanting to share on this.

KMEFA.

 

[EpsilonZero]

Guess no body gives a $hit about me spending time as a courtesy on want to share on this.

KMEFA.

What?

 

[inchtime]

Guess no body gives a $hit about me spending time as a courtesy on wanting to share on this.

KMEFA.

Thanks 174. I've just come back to this thread from last week. Helpful advice and convinced me to go with lithium ions instead of playing around with lipos to start with. I think the learning curve is easier! Hopefully mine will come next week and I can start making up the battery bank.

 

[KMEFA]

Thanks 174. I've just come back to this thread from last week. Helpful advice and convinced me to go with lithium ions instead of playing around with lipos to start with. I think the learning curve is easier! Hopefully mine will come next week and I can start making up the battery bank.

You are sincerely welcome.

 

[LSDOG]

why not use 18650 batteries?

 

[inchtime]

This is what I ended up doing. I used 18650 batteries to make a 20s6p with a BMS. Seems to be working fine but haven't finished the kart yet so no chance to properly test it yet.