Lead Acid to Lithium

[lettersize]

Guys, i am converting my cargo bike setup from Lead Acid batteries to Lithium.
1. Right now choosing between buying new 24v LiFePO4 pack or using Chevy Volt 24v modules which consists of LG Chem LiCoO2 pouch cells.
How do these compare? What technology is better for safety/# of cycles.
2. How do AH compare in Lead Acid and Lithium?
I was using 24v 100ah lead acid batteries and was getting about 8 hours of operation. To get same hours will i need 24v 100ah LiFePO4/LiCoO2?

 

[Jon NCal]

Lead is often rated at C/20, or 20 hour rate, but you can look up the discharge rating/tables/graph for your battery to make sure. So if the 100Ah rating is 20 hour and you are using it up in 8 hours, you may only be using 30 or 40 Ah because of lower actual capacity at higher rate of use. Therefore, you can go with a smaller replacement battery.

 

[lettersize]

Lead is often rated at C/20, or 20 hour rate, but you can look up the discharge rating/tables/graph for your battery to make sure. So if the 100Ah rating is 20 hour and you are using it up in 8 hours, you may only be using 30 or 40 Ah because of lower actual capacity at higher rate of use. Therefore, you can go with a smaller replacement battery.

Jon, thank you for your reply, I use these batteries -> http://dropproxy.com/f/C10
Did i understand this right - LiFePO4 24v 40ah battery will be enough to get 8 hours of operation of my cargo bike?

 

[Jon NCal]

Lead is often rated at C/20, or 20 hour rate, but you can look up the discharge rating/tables/graph for your battery to make sure. So if the 100Ah rating is 20 hour and you are using it up in 8 hours, you may only be using 30 or 40 Ah because of lower actual capacity at higher rate of use. Therefore, you can go with a smaller replacement battery.

Jon, thank you for your reply, I use these batteries -> http://dropproxy.com/f/C10

Did i understand this right - LiFePO4 24v 40ah battery will be enough to get 8 hours of operation of my cargo bike?

Well, your battery is rated at 10 hour rate, and looking at that discharge capacity data it looks like 95Ah or so at 8 hr rate. So, you are using more Ah than I thought. Perhaps ask the LifePO4 vender (e.g. pingbattery.com) what size battery you need. Do you ride 8 hours a day?

 

[wesnewell]

128 lbs of lead. Really.
5 of these in parallel will give you 100ah, will weigh ~26lbs and take up less space than one of your batteries, and should give you a longer run time.
http://www.hobbyking.com/hobbyking/store/__80907__Multistar_High_Capacity_6S_20000mAh_Multi_Rotor_Lipo_Pack.html?strSearch=multistar%2020000

 

[lettersize]

Lead is often rated at C/20, or 20 hour rate, but you can look up the discharge rating/tables/graph for your battery to make sure. So if the 100Ah rating is 20 hour and you are using it up in 8 hours, you may only be using 30 or 40 Ah because of lower actual capacity at higher rate of use. Therefore, you can go with a smaller replacement battery.

Jon, thank you for your reply, I use these batteries -> hhttp://dropproxy.com/f/C10
Did i understand this right - LiFePO4 24v 40ah battery will be enough to get 8 hours of operation of my cargo bike?

Do you ride 8 hours a day?

yes. it's a job. kind of cargo/delivery service.

128 lbs of lead. Really.
5 of these in parallel will give you 100ah, will weigh ~26lbs and take up less space than one of your batteries, and should give you a longer run time.
http://www.hobbyking.com/hobbyking/store/__80907__Multistar_High_Capacity_6S_20000mAh_Multi_Rotor_Lipo_Pack.html?strSearch=multistar%2020000

hm... had read Lipo is less safe comparing to LiFePO4. If i have to buy new would prefer LiFePO4 packs.
Or used auto modules for most cost effective option.
Does anybody know if i can use Nissan Leaf/Chevy Bolt modules to build 24v ~100ah pack.

 

[Syonyk]

You realize he asked about safety and cycle life, right? So Hobby King Fireballs should not be an option suggested.

==============

Lead acid suffers badly from the Peukert exponent: https://en.wikipedia.org/wiki/Peukert%27s_law

So, your 100AH of cells are likely not providing beyond 60-70AH. And, likely a lot less.

I'd start with about 50AH of LiFePO4 and see how it works, or 60-70AH if you'd like more capacity than you were getting.

Be aware that lithium doesn't sag like lead does, voltage-wise. So you may need to upgrade your wiring and connectors at weak points to prevent failure.

 

[wesnewell]

You realize that lifepo4 cycle life to 80% capacity is based on a <1C charge AND discharge don't you. Most is based on .2-.5C. As for safety, I've never had a problem in almost 5 years of use.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=27241

 

[dogman dan]

Instead of arguing lipo vs lifepo4, lets try to actually answer his question.

8 hours of use? Ok, what we need to know, or you need to find out to get your answer, is how much power you use now. The size of your lead doesn't mean a thing. We need to find out how many watt hours you use in that 8 hour day.

You have to get a watt meter to find this out. Then run a few days and see what you typically use. Then choose a lithium pack that will be about 20% bigger than you show your typical use is. That way, as it ages and loses some capacity, you are ok for a long time.

For professional use, I'd want a cycleanalyst on the vehicle, http://www.ebikes.ca/shop/ebike-parts/cycle-analysts/ca-sa.html

But you could get the same info with a much cheaper e bay watt meter. http://www.ebay.com/itm/Digital-60V-100A-Battery-Power-Analyzer-Watt-Meter-Balancer-For-DC-RC-Helicopter-/190863796444?hash=item2c705e68dc:g:x8gAAOxyaqlSTnip

Either one will work fine, but the cheap one would be hard to mount on the handlebars. For what you need to now today, the 12 buck watt meter located in the battery box will do.

Now for the guessing part.

You have now been using 24v 100 amp hour lead. This theoretically has 2400 watt hours in it. When people replace small lead batteries with lithium, they usually double their range, because 10 ah lead sags too much, and will not dish out 10 ah. But your large battery would not sag so much. My best guess is that you still need at least 2000 watt hours, which would be 24v 80 ah. This does not have to be a single 80 ah pack, it could be multiple 20 ah packs, or a pair of 40 ah. If you return to base several times a day, you could have two packs, one in use, one on the charger. Or three, two on the bike, one on the charger. Three 48v 20 ah packs could work real well for you if you can return to base twice a day. At all times you'd have 24v 40 ah on board.

Three 24v 20 ah batteries would also allow you to try three different types of lithium. You could then decide which lasts best, and continue to use more of whatever type or vendor worked the best, or more cost effective for you.

 

[lettersize]

Guys, thank you for all the inputs. Don't have time/equipment to test exact watt usage per dogman dan suggestion, so let's assume it's 24v 75-100ah range.

After digging ES(arkmundi's post was very helpful) and other sources come to that options:
1. DIY Lifepo4 pack made from A123, Headway, Panasonic or Samsung cells.
Sent the email to OSNPower for A123 quote. Contacted Headway. Let's see what prices can i get...
By the way are A123 cells brand new or old stock/refurbished, etc? Cause reading lots of claims that they are not manufactured any more.
2. Premade pack from Ping or Sunthing. Ping way to expensive for me. Sunthing sounds more affordable.
3. Building pack from used auto cells.(learnt a lot from Dave's blog) Cherry Volt 48v 45ah module can be rewired as 2p 6s into 24v 90ah module. Module consists of 12 'packets' each 'packet' 4v 45ah.
What kind of BMS will need for this?

Will dig dipper and see what numbers can i get.
Thank you for your help.

 

[dmwahl]

You realize that lifepo4 cycle life to 80% capacity is based on a <1C charge AND discharge don't you. Most is based on .2-.5C.

If he's taking 8 hours to discharge the pack, that's well under 1C. I doubt it's much more than 20-30A peak.

I'd check out the DIYElectricCar.com forums classified/for sale section. There are often people selling off lightly used LiFePO4 cells in the 40-100Ah range. If you can tell us the peak battery current that will help find a BMS. A 24V BMS should not be expensive for your application.

 

[lettersize]

If you can tell us the peak battery current that will help find a BMS. A 24V BMS should not be expensive for your application.

thx dmwahl, continuous current is 30A. peak current is 60A.
I am asking for BMS for this:

2p 6s Chevy Volt 24v 90ah module. Module consists of 12 'packets' each 'packet' 4v 45ah.

So i can calculate the cost of that option.

 

[dogman dan]

Ok, don't find out what you really use. Go ahead and buy twice the lithium you need. Likely it will only cost you about a thou for battery you don't need. You'd save your self at least an hour of time and 15 bucks. Sounds like a winner to me.

A junk cars battery could well be the best cost, but at the cost of maybe having a lot more than you need. If that's cheap enough, sweet!

Don't forget that you can parallel lead and lithium. So you might get what you need and a low cost with half new lead, and half lithium. This would cut your battery weight in half, while preserving the low c rate.