Motor and battery options

[Bgt2u]

Hi, l have built a homemade 48v vehicle that has two motors, two controllers, wired to a single throttle. It has a top speed of 35mph. I am considering switching to a 72v system. I am looking for more torque, and battery life. I realize that a 72v set up is more efficient than a 48v one. My question is, will one 72v motor give me the same approximate torque, as the two 48v motors, and since 72v is more efficient, will a 72v/20ah battery pack (powering one 72v motor) give me approximately the same range as a 48v/20ah battery pack powering two 48v motors? As of right now, l am using AGM type batteries, but will be switching to lithium type soon. I also am, and will be using the inexpensive 48v/72v motor/controller kits, from eBay. Also, l forgot to mention, my current 48v set up uses two 1800 watt motors (totalling 3600 watts), and the 72v set up motor would be a single 72v motor rated at 3000 watts. Any input would be greatly appreciated.

 

[Bgt2u]

Two MY1020 motors vs one

I built a little electric vehicle that is powered by one MY1020 BLDC 1800 watt motor driving each rear wheel. My question is: would it go further on a charge using just one motor (on a straight axle), or does powering two motors use the same amount of power because each motor's load is cut in half?

 

[itsid]

volt is not telling I'm afraid..

dumbed down to just below meaningful terms one could say
Volt makes speed and
current makes torque

the 1800W BLDC motors are in the 86-92% efficiency rating in their ideal powerband (rpm/load)
I doubt you can get amuyh better with a 72V setup tbh..
with a higher voltage (and thus way less current) and an overall lower poweroutput the chance of a similar torque dramatically drops.

Sure you can lower the gear ratio to accomodate for the different motor,
thus bring up the torque again and maybe even end up with more torque than you started with,
but the same effect would be achieved with just lowering the gear ratio a hair..

'sid

PS nice looking rig you got there...

 

[Bgt2u]

So, from what l gather, changing to a single 72v motor would not be any better for me than the set up l currently have......ls this correct? I still am wondering about range though. Would using one motor vs two drastically increase range, or would it not make much difference?

 

[itsid]

again.. how should we be able to judge?

you cannot reuse your 48V battery pack;

a battery pack with the same amount of Amp hours as the 48V batpack you have
would be ~50% bigger/heavier
and with the same electical powerdraw would have ~50% higher mileage

a battery pack with the same amount of Watt hours as the 48V batpack you have
would be about the same size/weight
and with the same electrical powerdraw would have the same mileage

Now, you reduce the powerout by ~16.7% (can't tell about electrical power since I don't know what motors you're talking about [would need a full data sheet to know])
so yeah ~15-17% higher mileage (7-8% higher range) might be possible all else being equal.

but it depends on the actual motors, the bat pack you are using and various other things
(do you need to change the gear ratio, in what way and by what amount does the overall vehicle weight change etc...)

But essentially it's as simple as
"you need X Watthours of battery to power X Watts for one hour or X/2 Watts for two hours etc."

How many watts you need changes with weight and gearing (and load),
how many watthours you have at your disposal depends on the capacitance of your batpack.
(it's size affects weight of course)

And electrical Watts as they've always been are nothing but Volts times Amps
and it doesn't matter at all
if you use 48Volts and 75Amps or 72Volts and 50Amps
both will draw exactly 3600 electrical Watts.
The motors will be different; as I said above...
the lower volt higher amp motor is likely to have a higher maximum torque,
the higher volt lower amp motr is likely to have a higher max rpm

Since ideally you will need to gear for the optimum range of the specific motor,
and again just simplifying to identical mechanical power output for each setup
the overall performance will be more or less identical
(same overall torque same overall top speed)

a single motor and single controller is slightly better than a twin controller twin motor setup
if the latter isn't well made to accomodate for load differences or worse isn't balanced at all.
Which I'm afraid I get the feeling isn't..
So I'd say a single motor setup would yield some additional minutes of driving with identical motor power.

Otherwise there'd be no noteworthy difference apart from the additional overhead powerdraw for the second controller.

'sid

 

[Bgt2u]

Wow, thank you for the very detailed information. After considering everything that you've told me, l have decided to leave it set up the way it is. I don't feel enough of a benefit would be gained by making motor/ voltage changes.The only change that l am going to make, is to switch from the 4-12v AGM 35ah batteries to a lithium-ion 48v 35ah battery pack. After doing some research, l believe that the lithium set up will give me a 30-40% longer run time than the AGMs will....due to AGMs can only safely can be discharged to 50%, while the lithiums can go to 80-90%. Therefore, theoretically l should get 30-40% extra run time from the lithiums with the same ah rating as the AGM type.

 

[itsid]

that's a very bad misconception about AGMs.. but yeah you have a weight benefit,
and while indeed LiIons can be discharged a bit deeper
you will not benefit from that at all..
since the controller has an undervoltage protection that kicks in anyways since it doesn't know if you run lead acid or lithium

anyways ~30% less battery weight

There is a drawback on high current discharge for lead acid batteries (incl agm, sla and gel packs) in which indeed the recovery rate is so low that you might have to stop for twenty to thirty minutes until the battery recovered to provide it's last 20% of charge or so..
some call it "get back home backup" that is usually not an issue you'll have with lithium packs.
but... a good lithium battery is teribly expensive, a cheap one terribly dangerous..
best of luck; I hope you don't buy cheap chinese packs
but one that's specifically made for high current discharge
(120amp minimum for your ~90amp peaks)
and not one made for a 250Watt bicycle motor or such.

otherwise you risk a meltdown
(and thus an inextinguishable lithium fire right below your testicles)!

LG had a nice video up showing why they do not sell lithium cells to end users ...
to not be part of home made batpacks... some very good points being made; it's on yt I bet

'sid

 

[Bgt2u]

I am considering one of these battery packs. Do you think either one will be a decent choice for my application? Just in case you can not see them clearly, they are on eBay. Item numbers:184160270289, and 184160345723.

 

[itsid]

both are a definite NO!
look at the peak discharge current listed
it's said to be 50 Amps...
50% less than what your motors are able to nominally draw and frankly they do draw more than 75Amps peak (more like 90 I bet)

So no, neither is a safe batpack for your kart.

AS I said you want one that's at least safe to draw ~120Amps peak from.
(a 100A pack might be on the edge but viable.. I'd rather dial in for safety however)

'sid

 

[Bgt2u]

I am glad that l checked with you, as l was going to purchase one of them. Now, my big problem is where do l even begin to find what l am looking for? I have not a clue. Maybe l should look into some Nissan Leaf batteries? All l am aware of is l will need a battery, or combination of batteries that total 48v, and deliver at least 30ah, and 120+ peak amps. Here is another (probably stupid) question, but can l get two of either battery packs mentined and just wire them parallel to achieve the same voltage, but double the amperage? I also noticed that the controllers are rated at 32 amps. Are they capable of more than that? Otherwise, l would figure (guess), that the maximum current both motors could draw would be 64 amps...ls this correct? If so, l would think that would definitely change my battery needs. Please be patient with me, as l am a newbie at this particular type of project. I am in no way questioning your knowledge. I just wanted to run by you, what is labelled on th controllers.

P.S. l did some research on the AGM batteries that l am using UB12350 (4 wired in series for 48v), and from what l can tell, the max current they can possibly produce is only 21 amps for an hour. If this is correct, than l am not even close to getting the amps my set uo requires with these batteries. If l am correct, then each motor is only getting a max of 10.5 amps? Please tell me this is incorrect. If it is correct, l am not getting anywhere near my little rig's potential.

 

[itsid]

Ah one must hate those stupid chinese sellers..

Now, for all I know the motor you're having is a BOMA 1800W BLDC (or equivalent)
and that has a peak power input of -as far as I know- 2200 Watts ( Iwas expecting more tbh)
2200 electrical Watts at 48V mean a current flow of 45.8 Amps per motor.
taking the powerdraw of the controller into account, let's round that up to 46Amps

So a 48V controller limiting to 32Amps would only yield a maximum of
1536 electrical watts and thus will be vastly underpowered for the motor.
(I bet they just copied the numbers from the 1500W controller.. but maybe they just sell crap *shrugs*)

yeah, what can I say? you need at least 92Amps for the two motors
(to unleash all their potential)
IF the controller is limiting, then you are limiting the motors..
possible, but not a smart thing to do unwillingly IMHO

And no, that's no dumb question at all!
Sure you can wire each controller/motor to it's own batpack;
or if you so desire parallel the batpacks to make a larger one
(making 2 48V 35Ah batpacks one 48V 70Ah batpack)

in which case the 50A peak is again on the edge..
very much so if the controller is allowing the full motor's demand to be drawn;
but perfectly fine in case the controllers are limiting your motors
to the ~1250 mechanical watts instead their nominal 1800Watts

max 21Amps for an hour is an extremely low number for an AGM
my tiny AGM (10Ah) needs to provide upwards of 50Amps to start my bike
and the last we got the specsheet of was happily providing 60Amps too,
yes, that means the capacity will drop far below their rating
the mightymax 22Ah only able to provide a measly ~8Ah
but they usually recover if left alone so you can squeeze another 6Ah out (at a significantly lower rate though)

anyways.. you can short out the AGM and cause a 200Amp discharge for a second,
it'll boil, it'll pop and it'll slowly drip warmish acid on the garage floor (don't! it's not pleasant!!)
repaint the chassis, clean up the mess.. start over.

do that with a Lithium battery and there will be fire; about the worst you will have ever seen..
having that under your bum... you cannot stand up from that thing quick enough.
and even if you just burned the garage down the kart is gone for sure.
So buy a QUALITY product, nothing else,
don't diy a batpack unless you are a trained professional battery builder.
don't buy the cheapest you can find since it's the only one you can afford.
even expensive packs have failed before.. most famous example the drone racing league champion of 2018 (he burned his apartement down with a fistsize batpack)
if you cannot afford a 700 dollar battery stick with AGM instead
or get wet cells...
wet cells are a tad lighter and provide a slightly better output ..
but they gas out more easily and spill more easily....
so they're not too popular for those "security reasons".
(some idiots complaining about wet cell being too unsafe happily solder around* on old laptop lithium cells... but stupidity spreads faster than knowledge)
personally I rather have some diluted battery acid on me [it's essentially stomach acid] than burning lithium

AGM is fine, it's a compromise but a good one to make IMHO..
for Lithium I'd only accept non 18650 packs,
(18650 exception: sony vtc6 cells @ ~8 dollars a pop)
but packs made of 40152S or similar

'sid

*lithium cells must never be soldered always be welded
(soldering is too slow they heat up and you just startet the first crack for them to blow)

 

[Bgt2u]

Once again, thank you for all of the detailed information. Yes indeed, l am using the BOMA motors. I did some looking around at the controllers that they supply with their kits. The 60v motor comes with a 32A (the same as the 48v controller, except for voltage), and the 72v motor comes with a 60A controller. Obviously they either under power the motors, or under rate the controllers. After considering all the advice that you have given me, l am going to try a different approach. I am going to stick with the dual 48v motors, as changing to a single 72v motor, does not seem to be beneficial. How about if l run one controller (rated at 100A) wired to the two 48v motors, and use a bank of Nissan Leaf battery modules? From what l can see, for a liitle more than the price that l would pay for 2 cheap Chinese packs, l could get a set of 7 Leaf modules, and maybe a charger. Those are rated at between 62-66ah, and have a high discharge current rate. What do you think of that idea?

 

[itsid]

idk while the leaf modules are certainly quality made..
you always buy used ones if you find them..
so you mostly can't tell wether they last or fail within months.
I honestly can't tell.

single controller is a bad idea unless you find one specifically made to power two motors
that would in fact be great.. I don't know any controller made for a dual motor setup
(well one.. but it's a unicorn you cannot buy anyways)

you cannot just pair cables and call it good, especially not with BLDC three phase motors.
So single motor controller on two motors is a bad idea,rather stick with individual controllers.

frankly.. I'd step up and get kelly controllers instead,
I think the KBS48121X [48V 55A continuous, 130A peak]should be a nice match ($99)
maybe one size smaller will suffice [48V 40A continuous, 110A peak] ](KBS48101X for $89)
https://www.kellycontroller.com/shop/kbs-x/

IDK your driving habbits, so I can't tell if you are more likely to rip the throttle or to cruise gently down the alley..
if you're cruising more you can save twenty bucks (still two controllers I'm afraid)
but frankly.. I wouldn't even bother...
you could step up to the next size Boma in the future and keep the controllers for example
So the larger one will certainly stay cool and relaxed no matter how hard you rip it

that's not too cheap, I know (compared to the 40 buck thingies)
but a good quality controller for a very fair price IMHO

'sid

 

[Bgt2u]

Wow, you are a wealth of valuable information! I clicked on the link that you provided, and agree that two KBS48101X's would be best for my application. I will get two of those, as soon as my budget (wife) allows. My driving habits are a little of both, some cruising, and some flat out nothing but throttle. My only concern now is the batteries. So is it a no go on the leaf batteries? If they are just a so-so idea, do you have any recommendations? Otherwise, I cannot seem to be able to find anything else that would put out my needed amperage discharge rate.

 

[wheels]

I am considering one of these battery packs. Do you think either one will be a decent choice for my application? Just in case you can not see them clearly, they are on eBay. Item numbers:184160270289, and 184160345723.

I was looking at those too. I actually purchased one to test with on my 48V 1800W system.

both are a definite NO!
look at the peak discharge current listed
it's said to be 50 Amps...
50% less than what your motors are able to nominally draw and frankly they do draw more than 75Amps peak (more like 90 I bet)

So no, neither is a safe batpack for your kart.

AS I said you want one that's at least safe to draw ~120Amps peak from.
(a 100A pack might be on the edge but viable.. I'd rather dial in for safety however)

'sid

And Now i am second guessing the purchase. Thanks for the knowledge share Sid. Questions though... are you saying the lithium packs are bad for his cart b/c he has two motors/controllers? or bad if he went to 1 72V? or just bad in general?

asking b/c the peak discharge is 50. If the controller is rated/limited to 32, doesn't that mean it would be safe for a single motor/controller setup? The battery packs also list an instantaneous amperage of 100.

While I'm at it... I've read a couple of posts saying 8ga battery wiring is plenty b/c of the 40amp rating. If the controller is pulling more than 50amps(continuous, peak, instantaneous, etc), wouldn't the wires need to be more like 2-4ga? Didn't mean to highjack the thread if I did.

 

[Bgt2u]

Hi Wheels....From my understanding, Sid is saying to be aware of the Chinese lipo packs in general. I believe that if you/l were to stay with a 32A controller, then the battery you purchased would actually work for a single motor set up. I think (don't quote me) that as long as the controller's continuous amp rating is lower than the batpack's continuous discharge rate, then it should be fine. The only question that comes to mind, is: are the eBay batpacks actually rated at what they claim to be? China makes false claims, and falsely labels many of their products, so proceed with caution. As far as the 8ga wire goes, you should be fine, as long as the length is kept under a few feet per wire length.

 

[JagLite]

Excellent information indeed!

I don't think it is only China made equipment that is often falsely labeled, it seems to be a worldwide problem. Buying from a reputable company is probably the best we can do to get what they say it is and what we are paying for. But even excellent companies can get lower quality from their suppliers. It is very difficult to keep high quality and stay in business with so much cheaper options available.

 

[itsid]

Well.. as I said above I cannot believe the 32Amp limit at all
in best case that'd be a 1500 electrical watt powerout, hence a roughly 1200W mechanical power.. (and you'd be 'wasting' 600 watts of motorpower for no reason)

I think it's more likely that some stupid employee just copied the number from a datasheet of a 1500Watt controller without knowing what english description was next to it.

It's not chinese quality that I warn about the most here btw.
it's if the poor guy translating and publishing the english specsheet without being able to read what he's typing, being told just to copy from a and swapping b to c then again..

that makes cheap chinese parts as dangerous as poor quality or craftmanship.

I happily suggest kelly controllers all day.. also made in china,
by a chinese company and I never heard any complaint about them being bad or anything.

batteries is unfortunately a totally different story.
some "recycle" factories for laptop abtteries and such sit in china
and tons and tons of batteries are delivered to their door.
And it's been heard that a few of those, just strip the cells and sell them if they manage to hold the tiniest charge..
sometimes resleeved with ridicule values, sometimes resleeved as sony, samsung or LG cells,
and sometimes as they are.

I wouldn't be too surprised if that batpack comes with used cells
if the price was cheap enough.

So.. if you want to know what amperage your motor draws, then measure it
(it's fairly simple to just by a shunt reader for a few bucks on ebay)
it'll measure the drawn amperage rather reliably
just tap into the battery line and read off the display..
chances are it's more than you'd expect

And that value (plus margin please) is what your batteries need to withstand,
not what someone -maybe mistakingly- put on an advert

'sid

 

[wheels]

Thanks Sid. Heading to ebay now for the reader.

 

[itsid]

make sure to get one with an external shunt
like that:
https://www.ebay.com/itm/LCD-Displa...olt-Amp-for-Cars-RV-Solar-System/402022634668
or here
https://www.ebay.com/itm/LCD-Displa...eter-Amp-For-Car-RV-Solar-System/254425404460
or for 15 bucks with a 100A shunt:
https://www.ebay.com/itm/LCD-Displa...Amp-for-Car-Vehicle-Solar-System/254419985639
(should suffice most of the time .. unless you also have a two motor setup)

more amps shunt: more better (less likely to pop on a peak current)

stay far away from everything less than 100Amps if you can

'sid