Lead Acid vs Lithium Ion -- Is an AH an AH?

[pediman]

I want to a 750 Watt Front Hub on a pedicab. Trying to decide whether to power with three 12V, 32AH Lead Acid batteries or a single 36V, 16 AH Lithium Ion battery.

The weight savings of the Lithium Ion is an advantage, however carrying 2-3 passengers the total weight load would vary from around 650-800 pounds, so the weight saving is more marginal compared with a more conventional bicycle application.

My main concern is RANGE with the two setups. From talking to others, the three 32AH Lead Batteries will last around a day working the Pedicab. Have not found anyone running the same setup with Lithium Ion.

Dealer #1 told me that AH is AH whether it be a lead acid or Lithium Ion battery. Dealer #2 told me that the Lithium Ion battery was far more efficient and that I could expect to see close to an identical range between the three 36 volt, 32AH Lead Acid batteries and the single 36 volt, 16AH Lithium Ion battery. I also saw some materials online that seemed to support Dealer #2 and explained it in terms of DOD (depth of discharge). The example used had the Lead battery only using 50% of its amp hours while the Lithium Ion battery used 80% which would then translate into a 20AH Lithium battery having the identical range to a 32AH Lead. 0bviously one of the dealers is wrong!

One solution I suppose is to carry and xtra 16AH Lithium Ion Battery and still save weight but first I'd like to know if that is really necessary. So is an AH an AH or are we comparing apples to oranges with these two types of battery technologies? Appreciate any help in this matter on which way to go.

Richard

 

[itchynackers]

It depends on your watt usage rate. The less watts you use, the closer the different batteries will be in terms of useable amp hours. The higher the watt usage, the less useable ah's the lead batts will have (Peukert effect)

 

[johnrobholmes]

If you were discharging the lead over a 10 hour period or longer, the first dealer would be correct. In reality you are taking the pack down in an hour or less, so dealer two is right in practice.

On an ebike, lead needs twice as much rated capacity than a lithium. The peukert effect kicks lead while it is down.

 

[pediman]

If you were discharging the lead over a 10 hour period or longer, the first dealer would be correct. In reality you are taking the pack down in an hour or less, so dealer two is right in practice.
-------------------
Not sure how I'd categorize the discharge rate of the pedicab but perhaps this might be helpful. During the course of a normal day we sit around a lot waiting for rides. So most of the "day" or riding the battery isn't being used. When I am riding, I plan on using the battery primarily on hilly portions of the rides which is at most 30% of the time. Since a lot of my work is tours, the average speed is often no more than 5-6mph, so it would be power on for the hills (while peddling some) and then power off and free wheel on the flats and down the hills. I rode a friend's motorized pedicab the other day on a tour and found that often I only powered on for maybe ten seconds to get a boost, then freewheeled for a few minutes, etc. Hopefully this will be helpful in gauging whether or not the Lithium Ion Battery in question will give me comparable range to the Lead Acid.

Richard

 

[johnrobholmes]

The lead may not be as effected by your situation since it can have plenty of recover time. I do not think that you would get the full rating of the Lead though. If the cash isn't a problem, choose the lithium for the lighter weight. If money is more of a concern get the lead.

 

[neptronix]

Think of it this way.
For an eBike application, generally.. take the AH of the lead acid batteries and cut it in half.

However, 16ah won't get you too far. especially since you will probably be using the throttle a lot, needing to carry all that weight. If you're on flat land, it would work well. If you're doing hills, the range will reduce a lot. I would guesstimate 30 miles for flat riding and 20 miles for hilly terrain.

Oh, and i must mention that a 16ah lithium battery may be stressed out by that amount of amperage. ( should be 20a nominal, but maybe peaks of 30a ). If you wanted to go lithium, lithium polymer hobby packs would be the way to go. They can discharge a LOT of amps, and are quite cheap.. They also are generally even lighter and more compact than regular lithiums also.

The downside is that you have to know what you're doing with lithium polymer.

 

[dogman dan]

Here's the real difference.

If you discharge the lead batteries 100% very much, you ruin them very quickly. like 50 cycles. If you make them last, that means only discharging them 50%. Hence the dictum that you get half the AH, even if you are being nice to them. Plus the weight. And the life span is no more than 500 cycles. 200 cycles is more common.

Lithium however, lasts up to 2000 cycles when discharged to 80%, and may still last 1000 cycles when discharged 100%. So you get less damage to your battery when you do discharge 100%, much lighter, and smaller, and the voltage drops less when the battery is getting empty.

But ,,,, if you must for money reasons, start out with lead and save for the lithium later. Maybe the price will drop by next fall. Just get a cycleanalyst, or other wattmeter, and make sure you keep depth of discharge between 50 and at the very most 80%.

 

[Ykick]

If you can deal with technical stuff, go with Lithium Polymer.

Another SLA downside - you mention sitting around waiting in between excursions. Never a good idea to use Lead hard then sit without at least trickle charge going back in. Sure way to reduce the cycle-life even further.

Seriously, you're already hauling a lot of weight so why pile on more Lead that's only going to provide 1/2 the capacity as rated?

I like eBike-Kit 9C motors and they have a nice 36V LifePo4 battery. While expensive, it's gotta good warranty, safe and would be alright for a slower machine.

Personally, I went RC Lipo and sunk my time/money into charging apparatus that not only safely charges my cells but has also taught me more about all types of batteries than I ever would have expected. Tuition money spent, if you will...

And now that I have the charging gear I need the actual cost of replacement cells is very reasonable. Especially considering that you actually get 5Ah from a 5Ah pack. By contrast my last set of 9Ah SLA's gave me 4-5Ah on a good day and the voltage sag was also most annoying.

Where do you Pedicab?

 

[Samba]

A spec sheet for a SLA http://www.batteryspace.com/prod-specs/SLA_12V35Ah.pdf
This one is 35AH, here theres no DoD issue, they are discharging the battery till its nearly flat - just for testing.

Look at the discharge characteristics plot. See the 35A draw line, it ends at 30 minutes. Its a 35AH battery - you'd expect it to put out 35A for an hour but you get half that. It does do 1.75 amps for 20 hours = 35AH and that 20 hour rate is whats stamped on the battery, but at 1C (35amps/35 amphours) you get 35*0.5hours = 17.5, or 21 amps for an hour = 21AH.

You get a bit of the same thing with lithium, but to a much lesser degree. You might get 10AH from a 10AH battery at a 1 hour rate and get 9AH from it if its discharged at a 15 minute rate.

As far as DoD goes, They are pretty similar. If you drain them totally flat then you'll damage them, if you want them to last you'll stop discharging when they still have a 20% charge left. If dogman is right about lead wanting to have 50% left, then you are getting 8AH from the 35AH battery, while a lithium 15AH discharged to 20% is giving 12AH.

So the 35AH lead battery could be replaced by a 15AH lithium battery if you are looking at a 20-35 amp draw. You save about 60 pounds with the lithium, that should knock an amp or 2 off your hillclimbs. But you'll want to check the amp ratings on the battery, some 15AH batteries don't want to do more than 30 amps for more than a few seconds at a time, you may want a 20AH because it can deliver 40 amps continuous. Thats true for many of the largest batteries, but it varies by brand and type.

 

[pediman]

First, want to thank everyone for their help. Quite a learning curve! Def leaning toward the vanilla lithium Ion for reasons given. Don't have the time to invest learning about the polymer version.

What do you think of this battery by Golden? (No direct link to the battery but if you go to http://www.goldenmotor.com/ you then just click on the battery photo.)

The version that I'm interested in appears to be a 36V/16AH and sells for around $500. Weight I believe is around 11 lbs.

Assuming that a 33 AH Lead Battery seems to do the job, I figure the 16AH would be about the right size and I could always spring for a second if necessary. The alternatives seem to be smaller batteries (half the amp hours) which would mean more batteries and I think more money.

So how does this Golden battery sound or any better options?

Richard

 

[johnrobholmes]

Contact Justin at Ebike.ca. He may have some better suggestions. It seems that eZee builds some of the best quality packs right now, per his experiences.

 

[Ykick]

I get really nervous ordering battery systems from China - motors/controllers not so much but the frequency of battery problems has me concerned in regard to warranty returns.

Now, I do buy Lipo from HK but that's a DIY assembly situation. Out of the 20-22qty Lipo packs I've purchased wound up with one dud but I never even checked into return. Simply not worth my time/trouble, that's why I bought extra.

As mentioned, Justin would be worth a shout, very knowledgeable, high character guy. I do own 2qty eBike Kit packs and they're a great 36V system. Trouble is, I just don't run much 36V that much anymore...

 

[John in CR]

Chinese battery warranty return is an oxymoron.

When it comes to lead vs any other battery chemistry an AH is not an AH, because lead batts are capacity rated at a 20 hour discharge rate. Lead can't deliver that capacity at higher rates and the difference is due to the Peukert's effect (http://en.wikipedia.org/wiki/Peukert's_law . There's no telling how long they've been on the shelf already, which probably means the rated capacity can't be delivered even over 20hrs continuous. Deep discharge kills lead quickly. Discharge without immediate recharge kills lead quickly. They're big and heavy. Lead as traction batteries is really only useful on forklifts, golf carts, and displacement hull boats, where the extra weight adds stability and there are quality batteries available. The lead batteries for ebikes are the same ones used for consumer UPS's and are junk, and they're only useful to get people with low budgets hooked on ebikes, though the rapid death rate and short range may turn as many off as turn them on.

John

 

[dogman dan]

Just to throw a curve ball at ya. There will be a marked improvement using a good quality lead 35 ah battery compared to a fair quality 12 ah battery that comes with some motor kits. Because you'd still be using only around a 20-30 amp controller, the strain on the larger battery would be a lot less, lessening peukerts effect, and making the battery last better, have less voltage sag, and allow a bit deeper discharges without damage. In a 35 ah battery, you'd be able to safely pull 16 ah or so out of it without much damage. Because of the large size of it, you'd be able to pull 30 ah out of it if you chose to.

With a larger motor, or larger controller, you'd have more problems using sla. The issue of sla not liking sitting through half the day part discharged would remain. The issue of sla weight is more than you think, it would weigh almost as much as an additional passenger. On flatter terrian, no big deal, but on hills it would be a big deal, just like it is with golf carts on too steep golf courses in the mountains. They go 36 holes easy on flat, and may not make 18 in the hills.

Assuming you go with one of the motors discussed on the other thread, clyte 4011, or 9 continent 2807, 20-30 amp controller, then a good battery choice for you could be a pingbattery.com 48v 20 ah. Discharge to 17 ah used or less if possible. Ping is one china vendor you can trust. But as always, you really can't send back a battery to china. But ping has the best reputation of those selling that type of lifepo4 battery. Even better to go bigger size, like 48v 30 ah, but that gets quite pricy.

If you went with a bigger motor or controller, then I'd steer you towards lipo from hobby king. Lipo might work well for you also, if you can return several times a day to a location where you could have somebody charging fresh packs for you. Then you could add capacity very cheaply with lipo, and only actually carry half of it.

 

[Lock]

During the course of a normal day we sit around a lot waiting for rides.

Yah might find there are "stray" electrical outlets all around you... In my town many *trees* along streets have 120V electrical outlets. Store signs, etc etc. Not all work but most do.
A little 48V 2A charger weighs about one pound.

Charging like this is called "opportunity charging". I have plugged into train stations and ferry boats and restaurant and bar patios, park utility sheds, sea walls, Christmas trees (Thanks Santa!)... it's a long list...

Here is a little map I made recently for my fellow ebikers, showing electrical outlets along some public docks in one section of an area park:

Cheers
Lock