How do Battery Booster Packs work?
- Thread starter ryan
- Start date
dogman dan
1 PW
Boost as in more volts? How much can your controller handle? You could boost range by paralelling the other battery, but it would have to also be a 72v pack, and as always, never hook a half charged one to a full charged one. Both need to be at very similar voltage when the connection is made.
ryan
10 kW
Sorry, I should've been more clear. I'm really only interested in increasing unassisted travel distance (w/o pedaling), not how fast I can get there. So more Amp hours than volts. I'd like to add to my current setup for special, longer rides.
adrian_sm
1 MW
What are the detail of your available battery packs?
If they are the same type of cells, and same voltage, it is easy. Just make sure they are both fully charged and wire them up in parallel.
- Adrian
If they are the same type of cells, and same voltage, it is easy. Just make sure they are both fully charged and wire them up in parallel.
- Adrian
ryan
10 kW
Current Pack: 72v20Ah (Dual 36v20Ah 12S2P LiFePO4 Headways)
I was considering Lipo for the second bike. Less volts (48?) but more Amp hours (20-30). Would I need to limit the second bike to the same chemistry and same voltage as the first if I ever wanted to hook it up as a parallel booster?
I was considering Lipo for the second bike. Less volts (48?) but more Amp hours (20-30). Would I need to limit the second bike to the same chemistry and same voltage as the first if I ever wanted to hook it up as a parallel booster?
John in CR
100 TW
You definitely have to have matching voltages as Dogman stated, so for ease of swapping things around you should run the wife's pack as dual 36's.
It's best not to mix different chemistries in parallel, because they have different discharge curves. To get a decent match of voltage with Lipo and your 24s Lifepo, you'd need something like a 21s pack of Lipo, which you couldn't split in half for the wife's ride. With the differing discharge curves what would happen is the Lipo would supply the bulk of the power early the ride, then the flatter curve of the Lifepo would take over until late in the ride where the Lipo would take over again.
Another route would be to put your dual 36's in parallel, and take the wife's pack and put it in series with your 12s4p of headways. As long as your controller can handle the new voltage, that could work, but you'd want a close match in capacity. You'd also need to monitor the voltage of both individually and avoid running one dry. I don't like this route.
The best would be dual 36's of headways for the wife too, but that ain't cheap. Personally I'd go economical and get the Lipos for me and set it up with a permanent 21s. Then assuming a 3.65V/cell top of charge for the Headways, for the long distance rides I'd charge my Lipos to 4.17V/cell, and put the two 36V Headway packs in series with each other and parallel that with the permanent Lipo pack on my bike. The Lipos and the Headways are individually sufficient to carry the load, so it's wouldn't harm either one. Plus the top of charge voltage and low voltage of the 2 packs are close enough that the whole thing works. The 21s of Lipo is a bit of an oddball for charging, so you'd end up having to invest in 24s charging/balancing capability for the Lipo.
Another route would be to never connect the 2 packs together. Make your run out using the lower capacity pack, and when that one is used up, turn around. Disconnect the depleted pack, and connect the full pack for the ride home. What I don't like about this approach is fully discharging a pack, though you could just make your halfway point 80% DOD of the smaller pack. The good part is that you don't have to worry about matching voltages, and you have more juice to get home than you used going out, so you're covered for a little headwind or a faster trip home.
John
It's best not to mix different chemistries in parallel, because they have different discharge curves. To get a decent match of voltage with Lipo and your 24s Lifepo, you'd need something like a 21s pack of Lipo, which you couldn't split in half for the wife's ride. With the differing discharge curves what would happen is the Lipo would supply the bulk of the power early the ride, then the flatter curve of the Lifepo would take over until late in the ride where the Lipo would take over again.
Another route would be to put your dual 36's in parallel, and take the wife's pack and put it in series with your 12s4p of headways. As long as your controller can handle the new voltage, that could work, but you'd want a close match in capacity. You'd also need to monitor the voltage of both individually and avoid running one dry. I don't like this route.
The best would be dual 36's of headways for the wife too, but that ain't cheap. Personally I'd go economical and get the Lipos for me and set it up with a permanent 21s. Then assuming a 3.65V/cell top of charge for the Headways, for the long distance rides I'd charge my Lipos to 4.17V/cell, and put the two 36V Headway packs in series with each other and parallel that with the permanent Lipo pack on my bike. The Lipos and the Headways are individually sufficient to carry the load, so it's wouldn't harm either one. Plus the top of charge voltage and low voltage of the 2 packs are close enough that the whole thing works. The 21s of Lipo is a bit of an oddball for charging, so you'd end up having to invest in 24s charging/balancing capability for the Lipo.
Another route would be to never connect the 2 packs together. Make your run out using the lower capacity pack, and when that one is used up, turn around. Disconnect the depleted pack, and connect the full pack for the ride home. What I don't like about this approach is fully discharging a pack, though you could just make your halfway point 80% DOD of the smaller pack. The good part is that you don't have to worry about matching voltages, and you have more juice to get home than you used going out, so you're covered for a little headwind or a faster trip home.
John
ryan
10 kW
Interesting idea of just using one pack at a time. I hadn't thought of that. Then I'd just have to ensure I get up to 72volts on the booster pack to match my Crystalyte 7240 controller.
Any tips on configuring a 72v20Ah LiPo pack in a way that's easy as possible to balance and bundle? Do I go after the larger packs to keep things simple? I'm a little overwhelmed looking at the hundreds of different options over at hobbyking.
Any tips on configuring a 72v20Ah LiPo pack in a way that's easy as possible to balance and bundle? Do I go after the larger packs to keep things simple? I'm a little overwhelmed looking at the hundreds of different options over at hobbyking.
John in CR
100 TW
ryan said:
Follow what the guys using Lipo are doing. Once I go that route, I'll get all the detailed work done just once and up front, by doing all the fine wiring to turn my permanent Lipo pack into one large pack with all of the parallel wiring to tie the sub packs in parallel all the way down to the cell level. That way I can bulk charge the whole pack with a powerful charger, and then regularly run the balancing overnight in one shot. That's tedious work with a pretty high risk of screwing up, but to me keeping all those sub packs separate like a lot of the guys do, ends up as a higher long term risk of screwing up, because you're charging and balancing a bunch of different packs. Even if you do your connectors to prevent connecting incorrect polarity, you couldn't eliminate the risk of paralleling a depleted pack with a full pack, and the big voltage difference could create a big dangerous flow of current.
For a beginner, the bigger packs would be better because it reduces the number of connections. Just to keep my options open for using the headways in combination for the long ride, I'd go three 5s packs in series with one 6s pack for 21s. Then multiply that by how much you need to get to ah capacity you want.
I'm going the other route with lots of small packs, because those are what seem to go on special sale for the absolute cheapest. Plus I want to build a bike with the lipo packs being a primary structural component for the bike itself, so smaller packs will make better building blocks for what I want to do.
John
