Minimoto build-up help

I picked up a Minimoto Sports Racer at a garage sale. It has the original 18V 180watt setup and a battery darn near dead. No sense in replacing without upgrading, right?

Here's where I need some help:
I want to end up with something that'll take my 90lb son to ~20mph and keep his interest. I have lurked this forum long enough to be confused.
Battery:
Should I go 24V or 36?
How many AH? [7,9,10?] Is more Voltage or AH important?
Motor:
is 300 watt enough?
Controller:
pretty clueless here, but like the cheap ones at TNC

If somebody can school me on a proven setup, I be grateful to get the bike running and my son smiling.
thanks in advance.

I'm not familiar with the bike but this is what I would do:

Use the stock motor until it melts down. We've doubled the voltage on our 200w motor and its still fine. Decide if you want more acceleration after you volt up.

Get the cheap 36v tnc controller. We've even used this one on 48v and its fine.

You might get by with small amp hour batteries if its the only way they will all fit. On our smallest bike we have 7ah batteries and with a light kid and low amp motor its fine.

If you upgrade the motor so that now the controller is doing the current limiting you may need to up the pack ah to suit. Its better if your current draw doesn't exceed 3 times the ah of your pack. 2x is better.

So a 15ish amp setup like ours does ok with 7ah batteries, but a 30amp setup would not. You would get big voltage sag under acceleration and pack cycle-life would suffer.

If you have big time and bucks to throw at the bike, forget lead batteries and check out some tool packs or lifepo4 batteries. Lead is bulky heavy and short-lived, but it is much cheaper and easier. Up to you.

20mph is pretty fast. Make sure your kid has the right gear! Our youngest has been riding a 20mph bike since he was two and a half, but he always has his helmet on.

If it looks like the one in the pic below except mines a Razor with a minimoto fairing tailpiece theres limited mods you can do to them without effecting runtime longevity or adding mega weight in better batteries and motors like when going up to 36 and 48 volts....extra weight will equal out the new power to almost what you had stock rendering it close to a waste of money when you factor in fabrication time to benefits........Those minimoto motors are 18 volt and a 24 volt motor with controller from a Razor would be a descent upgrade....Peace

Hi volts with a weak motor CAN go fast. Even 20mph fast. The downside is poor acceleration because of the low amp draw. For high volts with bulky lead bricks on a tiny bike you have to make a compromise somewhere.. Anyway, works for us. If you can find a way to fit more amp hours, "more power to you." :P

thanks for the rapid and helpful reponses!
First, Cam, it does look like the Razor you have. [And we also have a kart on the wall near it!]

So I think that the consensus is:
-go w/ 24V and 7ah
-add a 36V controller
-'overclock' the 18v motor until it burns up

where more volts is going to give me more RPM? and a slight boost in acceleration. But most gains in accel are based upon current - more AH, a controller that can pass it, and most imp a motor that can handle it. Right?

And the question arises related to current draw and your 2X and 3X multplier, Guido. Won't a 36V controller that passes 30 amps cause that sag? Does 2 [12V 7ah] = 24V 14ah? if so, the controller should allow all 14ah to pass thru to the 18V 150W motor. What would the ah consumption of that motor be?

Maybe on a mid size bike you can fit a 36+v 12ah pack, but duuude. Its pretty tough even on a mid, tougher still on a mini. We're up to 48v on our smallest bike and even with 7ah's its pretty tough finding more room. I'd like 60v 7ah but thats going to require welding brackets to fit em... But lead is cheap! So unless you pony up the bucks for fancier chemistry batteries you're going to have to deal with the bulk.

Also keep in mind when you volt up you ARE increasing your total watthours (energy) even though the ah is the same. What I mean is this- a 48v 7ah pack has the same energy storage as a 24v 14ah pack. You WILL go farther and run longer on a 48v 7ah pack than a 24v 7ah pack, make no mistake.

Motor and controller ratings are all over the place but I'll assume your stock 180 watt 18v setup is like 10amp continuous 15 peak. Sooo, your motor will probably not draw more than 15amps no matter how much current your new controller can put out. Its not a matter of the motor "handling it," it simply cannot pull more amps than its design permits. Example: if you hook up a huge 200 amp car battery directly to the motor its not going to try to pull 200 amps and instantly melt down. It can't. It will pull 15 amps and spin happily even with the huge battery.

Yes up-volting will improve accel as will up-amping. Will double the volts improve accel as much as double the amps? Maybe not but its still a good improvement in accel and as a bonus you get more mph. More amps can't give you both. Up-volting can be cheaper than up-amping also because of the reasons stated one paragraph up. Up-volting does not necessarily require replacing your motor or controller. Up-amping does!

You cannot run a 36v controller on a 24v battery pack. The low volt cutout protection will prevent the bike from moving.

Yes the multiplier thing means a 7ah pack will not be happy above a 21amp draw. Closer to 14 is better. Voltage sag is when you hit the throttle and your 36v pack suddenly only will put out 28 volts because it sags down 8 volts under the 30 amp load. Power output suffers as does pack longevity.

Like I said I would just give it a try with the stock motor on a 36v battery. The limited acceleration is kind of a good thing for a kid. Like stability control or something. You can always upgrade the motor after they get some riding time under their belt.

Got it.

So you are saying:
36V 7ah
36V 30amp controller
18V 150 watt [original motor]-not 180 as I thought

if I went:
24V 7ah
24V controller
original motor
would the improvement be so minimal that it wouldn't be worth it?

Dont get a 24v controller. If you want to give 24v a shot first, the stock controller can probably take it fine. I wouldn't even be surprised if the stock controller could take 36v. If you're going to toss the 18v stuff out may as well see how they handle it. If something does burns up its not expensive to replace.

As you have seen at tnc or ebay, 36v and 48v components are very cheap now. Higher voltage than that and it starts getting expensive. My kids have a while before they hit 90 pounds, so your results may differ from mine, but our guys are quite satisfied with over-v'd low amp setups.

Yep, that's my plan - start with 24V. replace things as they burn out and then add another 12 in series to get to 36.
thanks Guido.

oh, what kind of charger should I get for the 24V that also may scale to the 36V?

The only chargers that will do that are expensive and they require a 12v DC input rather than 120v AC. An accucel-8 would do it. Expensive but obsolescence-proof since it will charge ANYTHING. Highly recommended.

Or you could do what we do on a couple bikes here.. Instead of using the charge plug from the controller wire up your own pair of charger ports directly to the 2 halves of the battery pack. Like two 24's or 36 + 12 for 48v. in your case a 24v and a 12. More of a pain, but low budget guys work with what we got. You don't need to disconnect anything to charge with multiple ungrounded chargers (two prong) so its not too big a pain.

Side note- Its actually slightly better for the batteries the more chargers you use. If you used three 12v chargers instead of one 36v each battery is sure to get the same voltage. With a single 36v one battery could drift to a volt more or less than its neighbor over dozens and dozens of charge/discharge cycles. Not a big deal with lead though, probably not worth the trouble of multiple plugs.

You are a wealth of information, my friend!

OK separate chargers. How bout if I buy 12's and link them in series, and mate them with 12V chargers? Then buy another bat, buy another charger.
In that case what prongs [F1, F2, etc] and what guage wire is best for the link?

Thank you for the compliment. I'm a small fish in a puddle here..

Well, like I said its individual chargers are probably more of a pain than they are worth. I do the 24 + 24 and 36 + 12 thing because of necessity. Its what I got and I got bills to pay. On the one bike we do have a 48v charger for, its simpler.. no thinking required.

If you do decide to do multiple chargers you do not wire the charger outputs in series. I dont think thats what you meant, but just a warning in case it was.

You wire + and - leads coming off of each battery to a socket. You'll have 3 sockets for 3 batteries. Then you plug the chargers into those. You can use XLR or inline or molex or trailer plugs, whatever you want for the charge sockets. You do NOT need to EVER disconnect any bike wiring to charge with this setup if your chargers are two prong to the AC outlet. Most are. Three prong, take your chances.

You can use pretty much any 12v chargers for SLA as long as its low current. Don't charge 7ah batteries at more than a couple amps. Smart chargers are great because you don't have to forget to disconnect them..

Wire.. I use relatively thin cheap wire and it seems fine. Half of the doubled 16 ga. speaker wires works for low amp setups, for more amps leave them doubled up for 2x the current capacity without sacrificing flexibility. Or two pair of L+R speaker wire leads off of each battery terminal for 4x, etc.. Just twist all the leads together at the ends and crimp or solder on your connectors.

If you want to be pro looking you can go for the 10 or 12 ga. wire but its $$$ for the flex stuff and I hate the stiff stuff. Anyway I don't give a **** what our bikes look like and I'm ghetto fabulous. I had it laying around so speaker wire it is. When I run out of connectors I solder the f'n wires right on the battery terminals.

Terminals.. F1 or F2 doesn't really matter. Just get matching connectors.. but the bigger of the two is the standard.

Sorry for expletives yesterday, on a high from a coffee binge. Was trying to stress the fact that these are NOT motoGP bikes so go out there and have fun modding the heck out of them!!! It doesn't have to be expensive unless you want to go that way.

A neat option if you want the individual balance charger setup would be to use a four conductor trailer plug. That way you still would only have to plug one plug in, but you would have the benefit of the 3 chargers. Just twist the three charger leads together off of a power strip and solder on your four conductor plug at the end.

I guess you could do a six conductor plug instead of four if it makes it less confusing, but minimum you would have to use is four since two pair of terminals are joined. When you wire up your three batteries you will see what I'm talking about. You can get the trailer plug setup for cheap from your local auto parts retailer.

Heres some info I got when I asked a very similar question about a minimoto. My wife decided my daughter is too small for it yet (Not even 2yo) so I havent done it yet.

Hope it helps

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FYI our stock minimoto "500w" 36v controller didn't like 54v. I think I toasted it today. Ran fine on 48 for over a year though.