hard to believe

starrunner · #11 (**permalink**) 10-08-2009, 11:17 PM

Quote:

Originally Posted by deacon

I'm curious to see how much weight I can pull on one of my trailers. I might be able to pull that four hour battery pack in sla. Just need a big enough motor.

For every battery you add, the more weight you're adding and the faster the motor will drain them no matter what size it is, so it sounds like one step forward and two steps backward at all times. There really isn't all that much to think about.

jaeconsult · #12 (**permalink**) 10-09-2009, 05:17 PM

I can provide some close approximations of the two if you are interested. I have been working with sla's and lithiums for several years. A 12 ahr lithium is rated on a 1 hr basis and is approximatly the equilivant of a 16 to 18 ahr sla rated on a 10hr basis or an 18 to 20 ahr sla based on a 20 hr rate. You can store approximatly 30 % more energy in a lithium of the same amp hr rating and voltage as a sla rated at 10hr or approximatly 35% more than one based on a 20hr rating. The obvious plus to the lithiums are size and weight allowing a substantial increase in the range for the same size package due to the much higher energy density. The obvious down side is the cost of the batteries,BMS and the charger. In addition the lithiums can put out almost constant power then suddenly drop to nothing. For the bike to run 4 hrs on a 12ahr lithium pack it can pull no more that 3 amps and if it is a 36volt pack or 108 watts output for 4 hrs. If it is a 48volt pack it can provide 144 watts for 4hrs. This does not include hills or starts and stops. If running 17mph requires 200 to 250 watts the battery life is realistically 2.3 hrs. at that speed utilizing the motor only.

deacon · #13 (**permalink**) 10-09-2009, 06:41 PM

so what is they say about 250 watt motors on a 12ah lithium battery. Nothing larger they say whats that all about.

jaeconsult · #14 (**permalink**) 10-09-2009, 08:47 PM

You can run a 250watt motor on substantially more than 12ahr however if you hit the throttle too quick under locked rotor conditions or even high load condition and the speed control is unfused you may toast it depending on the controllers internal resistance, the motors resistance under locked rotor conditions and the batteries internal resistance and the operating voltage. If it is fused it will pop the fuse when the current is too high and protect the controller but this can become a nuisance. When I was testing motors and controllers I was continually subjecting them to overload conditions so I always put a manually resetable breaker equal in amps to the fuse the controller came with, then replaced the inline fuse with one 5 amps greater. The breaker would trip under high load conditions but since it was accessable while riding I would just reset it. I have only blown one controller due to this and it was one of my more expensive ones so I learned real quick to make sure everything is fused properly.

deacon · #15 (**permalink**) 10-10-2009, 10:31 AM

Quote:

Originally Posted by jaeconsult

You can run a 250watt motor on substantially more than 12ahr however if you hit the throttle too quick under locked rotor conditions or even high load condition and the speed control is unfused you may toast it depending on the controllers internal resistance, the motors resistance under locked rotor conditions and the batteries internal resistance and the operating voltage. If it is fused it will pop the fuse when the current is too high and protect the controller but this can become a nuisance. When I was testing motors and controllers I was continually subjecting them to overload conditions so I always put a manually resetable breaker equal in amps to the fuse the controller came with, then replaced the inline fuse with one 5 amps greater. The breaker would trip under high load conditions but since it was accessable while riding I would just reset it. I have only blown one controller due to this and it was one of my more expensive ones so I learned real quick to make sure everything is fused properly.

I'm sorry you misunderstood, or I stated my question incorrectly. I was asking about the lithium phosphate or Lithium polymer battery. The advertisement I read said the 12ah battery was for 250 watt motor the high amp hours were for larger motors. The question was why is this. In sla the ah of the batter is immaterial to the motor size. I have recently read that this is not true with the lithium ones. Something about their shutting down I really cant remember.

PS I have blown a few fuses in my time.

jaeconsult · #16 (**permalink**) 10-10-2009, 11:38 AM

The lithium battery packs typically utilize a PCM to control charge rate, provide a cutoff voltage for the battery pack as dicharging litium cells below a particular voltage in the range of 2.75 to 3 volts kills the batteries, cell balancing and pack temperature monitoring. All of these things are valuable to keep from destroying the batteries. Operation of a lithium pack without the PCM is dangerous to the operator as well as will destroy the pack. The less expensive ones just monitor charge rate and low voltage cutoff, but without the ability to balance the cells during charging the pack cycle life will be shorter( spend the extra $$). Unfortunatly the PCM's are current limited so if the current demand is greater than the PCM can supply it either shuts down or gets toasted or if it is fused the fuse pops. If you get larger than a 250watt motor under high load conditions the current draw can be great enough to cause problems for the PCM. If you want to utilize a motor larger than 250 watts with a 12ahr pack you will probably need to replace the PCM with one of a higher current rating or find one that has a higher discharge current capacity. Over the counter packs should have their max discharge rating and most of the 12ahr packs I am seeing are running in the 10amp range.

deacon · #17 (**permalink**) 10-10-2009, 02:05 PM

Then those suckers really are expensive since I run a 600 watt motor that draws 36amps. Thanks I'll mark those off my christmas list.

jaeconsult · #18 (**permalink**) 10-10-2009, 03:17 PM

Yes lithium set up with high battery current ratings can be really pricy in the $700 to $1,000 range for a 10ah 37V system, however if you are going to utilize the pack for several years it may be cost effective considering sla's have a limited cycle life of about 300 cycles depending on the %discharge/cycle and lithiums have a cycle life of somewhere around 3,000 or so they say. That would mean the lithiums are worth 10 times the cost of the sla's based on the life cycle. However with battery technology moving so fast I believe the price of the lithium will come down substantially in the next couple of years, so I design around sla's for now as they are rugged, and readily avaliable. If I was going to spend $$ it would be to increase the overall power system efficiency. There is some new lead acid technology out there but it will be a few years before it is in the retail stages. They utilize lead coated foamed carbon plates in lieu of the lead plates utilized now to decrease weight and increase discharge and charge rates. At this time from what I read they are being tested as starter batteries in big rigs.

karma1968 · #19 (**permalink**) 10-16-2009, 12:29 PM

deacon yes speed does come at a price. i give you the flying brick 250lbs max speed 68klm

at 110volts dc.

this bike is fun to ride

Recumpence · #20 (**permalink**) 10-19-2009, 11:58 PM

The highest capacity batteries readily available are Lithium Polymer (Li-po). I have a 5 pound Lipo pack on my recumbent that is 44 volt nominal (50 volts hot off the charger) 10amp-hour. It runs 20mph for an hour before recharge is needed. That pack is about the size of one typical housing brick. Four of those packs would be about the size of the pack you are describing and should give about 4.5 to 5 hours running on a 250 watt system with plenty of capacity left.

Also, you can get a 12S (44 volt nominal) 10amp hour lipo pack from Hobby City (without charger) for $350. That is a pack that will discharge 200 amps sustained. Lipo have gone way down in price and up in quality lately.

Matt