7s booster

[Gringo]

First up, I'll put this here as I'm not allowed in the technical section

I have a 2008 Agattu and after a reset my battery test shows 80% (4 lights)
I'm now finding Id like to use more assist without loosing any range and maybe gain some.

OK so I've just splashed out £115 on two 7s 5 amp lipos from hobby king, along with a charger and lipo alarm.
My plan is to fit these two in parallel onto the bike and keep the original in place.
During a longish ride when the original is nearly depleted I could switch over to the new battery.
I was thinking I could cut the original battery wires on the bike side of the connection and reconnect them with a XT60 connector, this would allow me to disconnect the original battery without taking it out of the frame and just plug the new pack straight in.
Alternatively, I could possibly fit a switch somewhere on the bike. I could then toggle between the two battery's whilst on the go.
I'm comfortable with both of those options but another I'm not so sure about would be to connect new & old together (when the are both fully charged)
The original pack would still be monitored by its own BMS and I could keep an eye on the new pack via a lipo cell cheeker.
I would charge the two packs individually, only connecting them just prior to a ride !

I've mixed, matched and rebuilt lipos successfully before in my RC cars but never played with more expensive bike battery's.
Any thoughts from the more experienced welcomed

This is what's on its way to me
2X http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=40090
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=45910
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=42953

 

[Geebee]

Your bikes battery chemistry is unlikely to be the same, it could prove to be an expensive and or dangerous test.
I like the idea of the plugs, I was considering it for one of my bikes, safe, no current handling issues and impossible to stuff up if you have a momentary lapse.

 

[patpatbut]

Please keep us update for your results.

I am also trying to boost my battery pack but using lifepo4 cells

I can post the results if anyone is interested

Pat

 

[Deleted member 4366]

That should work OK, but I think you need an additional wire. Flecc might come along and explain. If not, I think there's something on his website about it. IIRC the middle pin is also battery positive to the handlebar display.

You must make sure that you disconnect one before connecting the other.

When your Aggatu battery finally expires, you can pinch the BMS, which will work with lipos to make it plug-and-play.

 

[Gringo]

IIRC the middle pin is also battery positive to the handlebar display.

Yes the middle pin is there for the display. I did stick 24 volts worth of Nimh across the two outer pins a few weeks ago, just to see how/if it would run without the middle pin. It worked fine, just no battery display on the handlebars. A lipo alarm should sort that out.
On the one I have ordered you can customize the alarm to sound at a voltage between 2.7v~3.8v Per cell in 0.10v increments by pressing the setting mode button. This unit also features a handy built in LED display that will show the voltage of each cell followed by the over all voltage of the pack so I'll see its progress as I ride
I know lithium polymer cells in parallel will self balance, that's why whenever you connect two together, there voltages should be as close to each other as possible, if you connect a full cell to flat cell the full will discharge into the flat as quickly as it can, at best you'd damage the cells chemistry at worst it would catch fire
That's for individual cells, now what I am unsure about is the type of lithium cells used in my Agattu and about connecting the two battery's (new & old) together just via the main power leads.
On the two new 7s packs I will connect the balance leads together as well, effectively making a 7S2P 10 amp pack.

 

[Deleted member 4366]

There's a few theoretical dangers if you have the lipos and your normal batteries connected in parallel, so it's best to keep them separate, by adding a connector between the battery and motor unit, so that you can swap them over.

You can leave the two 5aH lipo packs permanently connected in parallel.

I wonder how it would go with 8S packs instead? I think I'd be tempted to find out.

 

[Gringo]

I wonder how it would go with 8S packs instead? I think I'd be tempted to find out.

You say that now I've ordered 7S
But seriously I don't know enough about the control system to risk over voting it.
Over on Hobbyking UK there's some 5.8A 9S packs for £32, I did consider buying them to split down to 7S and make some 2S packs for my RC cars out of the spare cells but it was late when I placed the order and I went for the easiest option

 

[DannyK]

Over the last few weeks I have been making some booster cells with old laptop 18650 cells. I have gone down the cutting the original battery wires route and it is working fine so far. I am not sure of the capacity but believe it to be in the region of 8ah.So far I have made 3 packs (2x36v and 1x24v) at a total cost of less than £30 Even if they don't last long it has been good fun.

 

[Gringo]

Well my bits arrived during the week and I've done a bit today.
For reasons beyond me, 7S lipos are fitted with one 3S & one 4S balance leads ? All ancillary items (charger, lipo alarm etc) have a single 7S plug.
The first thing to do is remove each pin & fit them to a 7S plug (one at a time) the red on the 3S is connected to the black on the 4S inside the battery, so on a 7S you don't use one of them.

On the bike I unscrewed the battery terminal and removed the connectors, these I replaced with a XT60 battery connector on flying leads, I did the same to the wires that originally went to the bike battery terminal.

With the flying leads threaded through the frame the battery terminal replaced and the lead that's attached to the bike battery block attached to the frame with a combination of cable tie, heat srink and some hot melt glue.

With the cover fitted, the loose XT60 comes from the bike controller and I have the option to plug it into either the original battery, or my new reserve pack.


I've been up the road for a quick test but I need to case & mount two of these packs before I can use it in anger

 

[alan blake]

I would put a fuse as close to the pack as you can , things go bad fast with these batterys ,
Bought that lesson

 

[Gringo]

Thanks for your concern Alan a fuse is a good idea.
Strange thing is, in the many years I've been using lipo's in RC I haven't yet had a mishap, I've had one or two puff up if I asked to much from them but never a fire or explosion. There's always a first time

 

[alan blake]

Hi , I found the wiring on controllers can be substandard and mine shorted inside, not as good as rc stuff anyway a fuse would have stopped my battery welding machine from becoming operational on the road side.

 

[Gringo]

Now all that left is a ride out
Last week I found an autoclave box at work that suited the battery's just fine, so I got busy with my tools and I'm ready for a distance test.
The plan will be to ride out on my new battery's, when the lipo alarm sounds (sits in my frame bag for now) I will change to the bikes original battery and head back home.
Anywho, here's how it looks.


Foot note
I popped out this afternoon on my new cells, I had 1/3rd assist on at all times & 1/1 for the hills.
The plan was to run the new battery's until the low volt alarm sounded and then switch to tho old one but after 22 miles I was back home and still on new cells