Wiring my scooter I fried my brain. Little help?

October 31, 2008 2:34 PM

Wiring diagram, can you help me sort this out plz?

So I'm back to working on the godzilla scooter. I've modified a 24v schwinn into a 48v beast. I'm finishing fabrication of the custom deck and platform, and I'm trying to make it so that I can stop taking this thing apart to charge it.

Scooter runs 4, 12v 10A batteries. I run it in series for day to day operation, 48v at 10A. I can't charge that though, and I'm not going to cough up the cash for a 48v 10A charger, and besides that's no fun. So, for charging, I pull the tabs off and rewire it as parallel and let the car charger go at it, 12v at 40A.

What I WANT to do is make this a switchable operation, but every time I start to draw it I confuse myself. I thought I had it figured out, but then I realized that because wires were touching each other at the battery, it would always be series, so I'm assuming I have to break the hot parallel leads between each battery, rather than in one place in the circuit (otherwise it's series by default.)

I realize that makes no sense, so I've added some pictures.
Picture 1 is the current setup. Very simple.

Picture 2 is the wiring setup, again very simple.

Picture 3 is where I want you to draw the lines for me. I've drawn it out about a zillion times. The switch is of the on-off-on variety, ideally one side is parallel and the other series. Of course, I'm going to need two parallel leads that I can surface mount to connect the charger to.

Again, I've got an gotten myself so confused that I can't even decide for sure what leads go to the breakable sides of the switch, but I've been assuming the constant/load point of the switch is going to be for neutral. I'm probably wrong.

Do I need to break the hots between every battery w/ the parallel side of the switch in order to prevent it from defaulting to series? (since there are only 2 contact points per battery, and they all have to plug in...even if they're not switched on they'll still be in contact...)

ALSO, help me maximize wire here and get rid of redundant cable if any. Your help is appreciated.

The next step for this scooter is to take a torch to the frame and stretch it a good foot or so to take it up to 72v, with a bigger controller and motor and rear wheel of course...and a bigger sprocket naturally. I think anything I do here is transferable though, it's the theory that's bogging me down.

(Yes this thing goes fast, no it doesn't overheat, and yes I'm marginally insane.)

Yea I realize this isn't a wiring diagram per se. If you respond with one, it might just confuse the hell out of me. But, you can certainly try! Thanks!

posted by TomMelee to technology (18 comments total)

I did something vaguely similar several years ago. I rigged it with a thought-up-while-drunk bus system.

Basically, I created a harness for parallel and a harness for series.
Every connection between batteries and motor for each harness went through a simple blade-type fuse connector. I epoxied all of these fuse connectors to a piece of wood (all in a straight line), then I added fuses and epoxied another piece of wood to the top of the fuses. Once I had done this for both harnesses I attached them to the batteries and motor without any of the fuse bars inserted.

The beauty of this system is that even a bozo like the one suggesting this could think of it and build it. The bad part is that it's ugly, stupid and required a lot of extra parts and bulk.

The fun part is that if you don't take out one fuse bar before inserting the other, you have an instant smoke machine.

You're probably much better off waiting for someone else to provide a slightly more elegant solution.
posted by terpia at 3:00 PM on October 31, 2008

You can't do this with a single SPDT switch like you have in the drawing. You'll need either a 6PDT switch, or a single pole single throw switch that controls 6 relays. The latter is probably the better option, as it'll put a lot less current through a single switch, and will also be able to scale.
posted by zsazsa at 3:02 PM on October 31, 2008

Zsazsa is right -- you'll need a 6PDT to make this work, and even then I'd be a little nervous because, as per terpia, you need all the connections to change simultaneously (or even better, you want them all to break in between making the new ones), otherwise there are switch configurations that result in a molten puddle where your batteries (and wires, and maybe shoes) used to be. If it were me and I were not feeling the death wish, I'd actually do 6P3T and use the third throw for a "center off" where everything's disconnected (if you actually find this mechanical switch it would probably be designated 6PDT-center off). You could also do it with 6 SPDT-center-off switches and gang all the switch levers together with a long rod so they're mechanically forced to point the same way.

And while I'm on the everything-blowing-up topic, please be careful when you charge in parallel like that. If you set the charger to charge at the single-battery rate, you're probably fine, but if you try to run at 4x the single-battery rate (theoretically safe since the current goes 4 ways) you're susceptible to a really annoying runaway failure where one of the batteries eventually is getting all the charging current, and again with the melting and the fire and the battery acid everywhere.
posted by range at 4:35 PM on October 31, 2008

I actually like terpia's solution. Bring all 8 wires to a terminal block somewhere, and have one thing you can plug onto it that both connects all the batteries in series and connectes them to the bike; and another thing you can plug onto it that connects them all in parallel and also attaches to the battery charger.

Alternately, get a 6-pole knife switch and an assistant named Igor.

I'd have the fuses permanently wired into one lead from each battery, though, so that (a) you still have fuses in the circuit when you're in charging mode and (b) if you drop something conductive onto the terminal block there's a bit of safety somewhere.

(Note that hooking them up in parallel could be a BAD IDEA if they're at different states of charge, since they'll try to equalize voltages with no current limit, and then the fire and melting and the jets of boiling sulfuric acid and stuff. Fuse also helps here.)
posted by hattifattener at 6:21 PM on October 31, 2008

You know somewhere in my madness I thought of the block solution as per terpia, but my general all around ignorance of the appropriate terms and places to look for parts sort of makes me have huge issues here.

Prior to this I'd say my most extreme hardware hackery was soldering redboxes out of ratshack tone dialers in the mid 90's w/ crystals from Mouser.

The switch I bought today while not actually paying attention was a 3 throw, on-off-on switch. It would work I think but the amperage allowed is too low. (30A)

Can any of you provide me any assistance w/ finding any of the parts you speak of via mouser or some other supply house? I understand the lingo but I don't know it off the top of my head.
posted by TomMelee at 7:47 PM on October 31, 2008

You can do this without any switches by just connecting the 12V charger to one pair of battery terminals at a time. You don't have to disconnect anything. But it means you can only charge one battery at a time.

Or else you can buy a 48V battery charger for 15 bucks on ebay, which is probably less than you're going to spend building a switching mechanism.
posted by JackFlash at 8:17 PM on October 31, 2008

Jack-it takes about 1.5-2.5 hours to charge one battery from dead to full, times 4 plus being around to do the switching, which means that realistically it takes a couple evenings to get 4 batteries charged, more when I move up to 6 or 8. Sucks.

I have looked in the past for a 48v charger on ebay that was capable of 10A, but have not yet found one that was affordable. I accidentally bought one that I thought would be perfect, and then realized it only went to about 3A, which leaves me with discharged batteries. Also, 48V is only good so long as I have 48V, moving to 60/72/84 will leave me useless again. Besides, doing it myself is so much cooler than having some built in mechanism. ;-)

I spent some time on mouser last night looking for switches, they have several 6p3t switches, but I can't seem to find an amperage rating.
posted by TomMelee at 6:18 AM on November 1, 2008

Perhaps you could make the 48V charger, instead of the switch between parallel and serial?

My sleepy head says that a rectifier and transformer could do this.
posted by garlic at 7:13 AM on November 1, 2008

Perhaps the problem is your understanding of the battery specs. I'm guessing that your batteries are rated 12V and 10 amp-hours. This does not mean that you need a 10A charger. 10 amp-hours means it takes 1 hour to charge with 10 amps or 10 hours to charge with 1 amp. A typical scooter battery charger is about 2 amps so it will take roughly 5 hours to charge the battery if it is fully discharged.

So you only need to get a standard 48V - 2 amp battery charger for about $15. This is less than the cost of a single battery. If you go to 72 volts in the future, just buy two $15 chargers and connect them at the same time across each set of 4 batteries in the string. You don't need to disconnect anything.

When you charge your batteries in parallel as you are proposing, you need much more current. Four batteries at a time with a 3A charger means each is only getting 0.75A. This means it takes over 13 hours to charge all four batteries. No wonder you didn't think it worked. When you charge using a 48V - 2A charger with the batteries in series, all four batteries get 2A, so it only takes 5 hours.
posted by JackFlash at 9:55 AM on November 1, 2008

Sorry about that. For 72 volts, you need a 48V charger and a 24V charger. The first you connect across four batteries and the second you connect across two batteries. You don't need to disconnect or switch anything. In any case, the charger will cost you less than a battery so there's no reason not to do things the easy way.
posted by JackFlash at 10:03 AM on November 1, 2008

Jack, thanks for the explanation. Much appreciated. Interestingly, the 48V charger I bought showed me a green light indicating full charge. I will reinvestigate. Thanks for the heads up.

Unfortunately, the built-in-charger-pronger for my setup is a female receptacle and the charger is also a female, so I had chopped off the correct end from my 36v charger and apparently done it backwards first, there was a nice pop and a tuft of smoke from the charger. However, the multimeter still said that it was pushing 48v, so I used it under supervision. I will try again though! That might be the golden ticket.
posted by TomMelee at 12:23 PM on November 1, 2008

... there was a nice pop and a tuft of smoke from the charger.

That is usually a sign that you've let the magic smoke escape from your black box and it won't work anymore. To test, use your multimeter to measure both the voltage and amperage. Note that to measure amperage you must connect the meter in series with the batteries, not across the terminals like you do for voltage. Your charger should put out the rated current, probably around 2 amps.
posted by JackFlash at 12:40 PM on November 1, 2008

I need to clarify this Amp-hour rating vs. charging issue, because you could get in a reasonable amount of trouble.

The Amp-hour rating of a battery measures its total stored energy when fully charged -- a 50Ah battery can deliver 10A for 5hours and would then be dead. (If it's a 12V battery, then that means the total energy is 12V * 10A * 1h = 120 Watt-hours.)

You can use the Amp-hour rating of a battery to figure out an appropriate charging current. For lead-acid batteries people tend to aim for somewhere between C/10 and C/4, or in other words the rated capacity (in Amp-hours, you hand-wave and just forget the hours) divided by something between 10 and 4. For a car battery (~50Ah) that means charging somewhere roughly between 5 and 12 amps. You can also check out the full gory details. Note that if you work the math backwards, it means that you want a full-charge time of between 4 and 10 hours regardless of battery size.

So -- whatever you do, don't try to charge the battery in an hour by using the capacity itself as the charging current; it's way too high and you risk explosion. It also means that you can't build a quick & dirty 48V charger by just building a 48V power supply, because what you need is current control as well.

So far the sanest ideas I've seen here is either building two separate wiring harnesses (pull off one, replace with the other to charge) or using Igor-style knife switches ganged together (knife switches will handle the current load better) -- at the high currents you have, even switches rated for your maximum load are going to fail remarkably fast. I say this as someone who watched a 400A mercury-dipped relay fail in a month of use on a suposedly-200A load; we had to replace with a 1000A-rated relay to get any life at all.
posted by range at 2:14 PM on November 1, 2008

So far the sanest ideas I've seen here is either building two separate wiring harnesses (pull off one, replace with the other to charge) or using Igor-style knife switches ganged together

That is exactly the wrong thing to do if you want to properly control the charging current. If you charge in parallel, then the charger current is divided among all the batteries. If you want a 2-amp current, then for four batteries you need an 8-amp charger, which is going to be very expensive, large and heavy. You can only hope the current is divided evenly. If one battery goes bad (high resistance), then the other batteries are going to get more than 2 amps which could damage them as well.

Typical scooter batteries are about 10 amp-hours so you want a 2 amp charging current. The proper way to do this is with a 48V 2-amp charger connected in series. It will guarantee that all four batteries get no more than 2 amps, preventing damage. But equally important, it is much cheaper than a 12V 8-amp charger. Why fool around with a high-current 12V charger that might destroy your batteries when you can do the job properly with a very cheap 48V charger (charger price is roughly proportional to output current, not voltage).
posted by JackFlash at 3:18 PM on November 1, 2008

So...magic updates galore. (And thanks for all the help!)

Went after the charger w/ the meter today and guess what, lighting up @ the charger doesn't indicate that it's actually throwing power. (It's not.)

So now I'm charging at 36v with the 36v charger on 3 batteries, and when it's done I'll swap the uncharged for a charged and let 'em equalize. I will order another 48v charger. HOWEVER, here's the issue:

This scooters inline charger adapter is of the XLR type. I cannot find a 48v XLR charger that isn't over $150. My attempt to cut off the charger end from the 36v and put it on the 48v resulted in me getting it backwards and cooking the 48v charger.

So...anyone wanna help me decide which of the two XLR wires goes to the hot lead from the charger? I'm sure there's a diagram somewhere, but I don't see it.

Oh and the custom fab of the housing is done...ish. When was the last time you saw an electric scooter rocking woodgrain?

Thanks again folks.
posted by TomMelee at 3:22 PM on November 1, 2008

So...anyone wanna help me decide which of the two XLR wires goes to the hot lead from the charger? I'm sure there's a diagram somewhere, but I don't see it.

You've got a multimeter right? Positive side of the charger goes to the positive side of the batteries and the negative goes to negative.
posted by JackFlash at 3:52 PM on November 1, 2008

Oh, sorry, should have been clearer -- the premise behind all of this is "I want to charge in parallel" -- and he can, but only if he limits the charger to the charge rate for a single battery (which will quadruple the charge time).

I already said somewhere up above, in an earlier dire warning, that if you charge 4 in parallel at 4x the single-battery rate you leave yourself vulnerable to a runaway failure in one of them. If you current-limit yourself to the single battery rate, then the worst case scenario is a runaway failure that causes one of the batteries to charge at the correct rate. The downside is obviously that you're intentionally setting a 40-hour charge time instead of actively current-limiting each battery separately (or in series).
posted by range at 4:32 PM on November 1, 2008

How do I know what side is the hot side of the plug when it's not connected to anything? I'm assuming I can actually test the receptacle holes and see which have a voltage when it's not plugged in and which is neutral, but that still doesn't tell me which of the wires poking out of the back of the XLR go to which prongs.

I suppose I can figure out wire is hot on the 36v charger and make that the hot lead from the 48v...

Is there something simpler I'm missing? Sorry for the long delay, my going away party was last night and we got a little out of control.
posted by TomMelee at 5:40 PM on November 2, 2008