How does one run 72 volts as 36?

[MikeFairbanks]

I looked for a previous thread by Uncle Ron, but wasn't able to find it. I thought he wrote that he used two 36-volt battery systems, but ran them in a configuration that kept them in balance to where the draw was taken equally from each. In essence, a long-lasting 36-volt battery.

If that's possible, I might try it with the electric tricycle we built. It works great, but I can already see the limitations of the 36 volts. However, I want to keep it legal, of course, and am not looking for speed so much as torque and endurance.

I hope I explained that.

Any ideas? Currently we're running 36 volt SLA, front wheel hub motor (ebikekit). Another 36-volt battery setup is inexpensive.

 

[spinningmagnets]

I believe you're describing a "parallel" connection. If you dont want to solder the two battery cables together, you might be able to purchase or make a "Y" cable-connector. Short adapters like that are sometimes called "pigtails". Read up on these first to ensure you dont damage your batteries by being in a hurry (like me!)



Heres a parallel-Y-connector for LiPo packs, resulting in the two packs having the same voltage, but twice the range (a "series" connection would result in twice the voltage, at the same range as before):

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7880

 

[BLUESTREAK]

Since you have the (E-BIKEKIT) and the 22amp controller you can do 2 things (1) have STEVEO upgrade it to 35amp or(2) get the 72volt controller fron LYEN and have the LOW VOLTAGE CUTOFF set for a 36 volt battery and add another 36volt SAL like SM sugested. You have plenty of room on the trike and this will give you more amps for power.

 

[Rassy]

Mike, your statement "I can already see the limitations of the 36 volts" is a little ambiguous. If you mean you just want to go further without running out of juice, then what spinningmagnets wrote is what you want to do. You would still be running a 36 volt system, but with a total of 24 amp hours available.

But since you mentioned 72 volts, limitations, etc., are you looking for a little more speed and torque? If so, you would want to just add one more 12 volt battery in series with your other 3 batteries. This would give you a 48 volt system which would increase your top speed by about 1/3. It would also accelerate a little faster, etc. But, you probably would not get more range because you would have a tendancy to use more power.

I recommend you do try to run with 48 volts for a while, since then when you are ready to upgrade to a lithium (or?) battery you will know whether you want 36 volts or 48 volts. My original system was a 36 volt sla kit, which after about a year I tried using 48 volts. The 48 volts was a great improvement, and I never went back to 36 volts. If you have LED's on your throttle that indicate the battery status, they will no longer be effective for 48 volts. I just cut the high voltage wire going to the throttle, and with the LiFePO4 that I use now that type of indicator is meaningless anyway.

 

[Samba]

2 ways

You can make another 36v - thats 3 x 12v - and then connect the new 36v neg to the old 36vneg, new 36vpos to old 36vpos

Or

You can connect each new 12v to one of the old 12v -

If you connect 2 batteries like this, in parallel, you add together the AH ratings and treat it as a single battery with the combined AH.
The new batteries should have the same chemistry as the old ones, SLA
They could be of different size - you could pair up a 20AH and a 30AH for instance - making a 50AH.
You would want to make their charges equal before you connect the 2 - the easiest way is to fully charge both first.

If you are drawing 20A from a 20AH SLA - 1:1=1C you may get only 12AH(60%) from it - they don't like putting out so much current.

If you keep drawing 20A but make the battery 50AH, 2:5=0.4C you will get more of its capacity - around 75% or 37.5AH because the current relative to the capacity is a more comfortable rate for SLA.

 

[MikeFairbanks]

I don't need more speed or more torque really....what I want is less fall off after a few miles.

I certainly don't want more speed. Our path system has a speed limit of 19mph, so any more than 20 is not good. Obviously 22-24mph isn't the end of the world, and downhill it can't be helped sometimes, but I don't need more speed. What I want is for the power to last a little longer.

I'm not even looking for more range (although this would inevitably happen with parallel 36-volt systems).

 

[Rassy]

Mike wrote:

What I want is for the power to last a little longer.
I'm not even looking for more range

Ok Mike, now I see why you confused us a little. For the power to last a little longer is exactly what more range means. So you just need to add another set of batteries in parallel like spinningmagnets posted above. You don't need to make any changes to your controller, etc. You can also use the same charger and charge both batteries at the same time. Of course it will take a little longer to charge if you have used more juice.

One of the above posters talked about the two ways you can hook up six 12V batteries for a 36V system. The way spinningmagnets illustrated is the easiest, but I have seen some "experts" argue that first paralleling the batteries in pairs and then hooking up the 3 paired sets in series is the best way to go. With SLA, it really doesn't make any difference, except if a single battery fails, it may ruin both of it's parallel partners in the first setup, and only it's one parallel partner in the second setup.

Edit: When hooking up these batteries packs in parallel, work very carefully. You won't get a shock, but if you short the batteries in any way, a lot of heat is created almost instantly. This heat will melt connectors, tools, and rings, resulting in severe burns. Most of us know this from experience, including myself. It's a good idea to remove rings when working on multiple battery wiring. Adding fuses and/or circuit breakers to the system can help, but does not eliminate all potential problems.

 

[Samba]

your 36v battery starts off at about 39v, When you draw 20 amps the voltage 'droops' down to below 36v. This droop gets worse as the battery is discharged. If you doubled up the batteries they would each see only 10 amps of that 20amp draw and droop less.

From 39v fresh from the charger, the battery voltage will drop as its charge is used up down close to 36.5v. When its low, a current draw could make it droop as low as 30v.

The lead batteries 'drop' less than most than others - from 2.15 volts/cell at 100% to 2.05 volts at 20% charge is about a 5% drop. The lithium battery voltage drops close to 10%. But the 'droop' when current is drawn is notoriously worse for lead batteries.

Your amps are limited by the controller, amps * volts = watts so as the volts drop and droop you have less watts, less power.

If you wanted constant performance, you'd need a way to boost up the current limit as the voltage decreases - .

Doubling up the battery will decrease the effect. Less droop because each sees fewer amps, and less drop because your batteries are always closer to full.

 

[dogman dan]

Pretty sure increasing the speed of the trike much would get dangerous. You can just add one more sla and go 48v without damaging the controller. This would give you 25-27 mph top speed, but better performance on starts and hills or hauling a passenger.

You would have to have a smarter throttle hand than I do. I often ride full throttle, and have to really think about it to just ride a set speed. But it would be worth it, to get another sla and see how you like 48v. Most of us like it!

 

[torker]

Now Dogman he does not want more speed. He just wants to delay the peukert effect a little longer. 48 v is fun though. Although I am not too sure I would like 25+ mph on a tall delta

 

[MikeFairbanks]

The trike is currently running at about 20mph on the flats. There's no way it's getting anywhere near 25mph. I'd know it for sure. I'm not using a computer yet, but I've ridden for years (with and without computers).

The trike weighs a hundred pounds, the battery thirty, the hub motor probably twenty, and the box I put on it another thirty. So we're talking 180 pounds. Add my 200 pounds and you can see why it's not going to hit anywhere near 25mph on 36volts.

Even at 48 volts it would probably top out at 25mph.

On the straights, it's not a problem, and you learn pretty quickly how to turn the trike safely. You can turn at high speeds, but not sharply. You have to get a feel for it. It's very fun.

Now at slow speeds (even as low as 1mph) you can turn in complete circles while seated upright with a bunch of groceries in the back.

Like I said before, for people living in smooth and flat conditions, a tricycle has a lot of utility to it, especially these Worksmans. You can do real work with them. 48 volts wouldn't be overkill. These are industrial tricycles...very heavy. They aren't like your typical Schwinn Meridian that is much lighter. The trike I'm using is very heavy. Off the line it barely moves, which is why I have the three-speed hub motor on it. I use the lower speed to build up some momentum, and then slowly ease in the throttle. Works like a charm. But I bet it wouldn't do well if I stopped on a hill and continued without giving it a little help.

I don't want 48 volts. I just want 36 volts with less fall-off. That's all. Just want to keep it simple and fun.

Now, when I get my next build going we're talking a whole different ballgame. I rode IceCube57's bike today (72 volts, I think, and a Phoenix Racer on the back). He running Lipos and that bike is a monster. I couldn't believe how much power it had. I only rode it half a block and easily had it at 25mph without much throttle. Very cool.

 

[BLUESTREAK]

Since you don't want 48volts just get 3 more 12volt lead acid,series hook them. up and then do as SM described above paralell the two 36volts and this will double your amp hr. and not have as much voltage sag. plus it should provide more amps for pulling power. also it does not change your voltage to 72volts as you describe in your TITAL.

 

[MikeFairbanks]

Groovy, groovy. Thanks everyone. I'm excited. Since this trike can handle a lot of weight the extra 30 pounds won't make that big of a difference (but provides more stability).

I'll update when I get the extra pack hooked up (still have to order it).

 

[dogman dan]

Yeah, you just need a better battery then. More sla or something better for the voltage sag. Because I had a range problem I ended up going straight to a pingbattery after about 2 months. That cured the voltage sag. So if funds are ever avaliable, a 36v 20 ah ping would be ideal.

My suggestion to try 48v was based on the cost of one more sla being a lot cheaper than three more. You might look at finding some fairly cheap slas to use if you decide to just go bigger. Perhaps something in 7 ah?

Even though the trike can carry em, I just hate to see you invest too much more into dang sla's. If you can scrounge some, that's different. If you can scrounge some nicads, I found they worked great paralelled with sla.

5 ah of 10s lipo from hobby king and a very cheap charger might be a better investment, if you have about $200.

 

[MikeFairbanks]

One more 36volt setup run in parallel is all I plan to do for this project. I don't mind spending a little extra on it (I've only put in 8 dollars of my own money) and it will help considerably while keeping the speed safe. I would like a little more torque on the hills, but it hasn't stalled yet. Like I said, on a full charge it can definitely make it one-way to work in cold weather. That's been proven, so even if I do nothing it will be fine. It would be nice, however, to add a little more to it for endurance and range. I know I said before that range wasn't an issue, but I guess it is, especially where I live (big hills).

I can't even imagine what it must be like to live in San Francisco. If you've been there then you've seen what hills can really look like: hills so steep that the sidewalks have steps. No joke. And the garage doors aren't rectangles. They are trapezoid-shaped in order to fit the hill.

 

[amberwolf]

Only thing I recommend is that you sling all the SLA under the trike's rear axle, just forward of that axle, if you can. It'll help with the stability during turns and whatnot. It's not much counterweight, but every little bit helps.

If you can, you should also put some of the cargo tray/boxes (if any) down under there, too, just high enough to clear things you expect to ahve to pass over. Then when hauling any cargo that will fit in them, you can put it down low and it will ride a little better in turns.

 

[dogman dan]

One of the reasons I went to lifepo4 was that I had to climb 1000 vertical feet to get home. 3 sla's left me with a dead battery 4 miles from home. 4 sla's left me dead 5 miles from home, and 4 slas and some nicads left me dead 5 miles from home. Adding much weight going up the hill was not helping me any.

This was with a brushed motor though, that really had a hard time climbing hills, so your experince may be different. You will climb better with 48v, so you could just add one battery when you get to the hill.

Upping the voltage will up the watts and that will give you more torque, as well as more speed up the hill.

 

[torker]

Sounds like with all the paths and no real hills I would keep it at 36 v and keep the speed down anyway. Speed will use those extra watts anyway.