NZer on hybrid

[duivendyk]

I tend to agree,it was a ploy to sidestep the paralling problem,amalgamate&conquer so to speak.I concluded that the possibility of the batteries crossfeeding (one dragging down the other) is pretty remote if you start out with fully charged ones and the capacities are not significantly different.So if one type bites the dust,that's not the end of the world,it just sits there and goes along for the ride.

 

[Fuzzo]

The arrangement I was considering was a plug for each pack. Then either one or both in parallel can be connected or disconnected at will. So I can disconnect any pack that is depleted. Probably the SLA pack first, which already has a power switch.

Currently, I can usually sense depletion pretty easily, because my legs are taking up the slack. My heart rate monitor picks it up ;-). I'm not so sure how this would work with 2 packs, so I'll definitely take my multimeter along on the first few rides and check both packs, just to see how they're faring.

 

[duivendyk]

If you're interested in the battery currents,I can give some advice on how to monitor them without actually putting a Am meter in the circuits.Involves fabricating very small resistor (10 milliOhm or so) and measuring voltage across it ,10A through 10 mOhm is100 mV or 0.10 V.Put in battery leads preferably at negative(ground side).Then able to measure battery currents and also difference between them.Resistors can be made from copper wire,need to solder on lugs and epoxy it all togethe (JB weld works well).Need to find copper magnet wire,best sizes AWG 21 through 26 (diameter 0.72 mm through 0.40 mm).Can give info as to reqd. length.Question:Can you measure these low dc voltages (100/200 mV) with your MM?

 

[woody]

Mixing batteries

This is not completely in tune with this thread however..............

I read that mixing batteries changes characteristics of both.

Has anyone tried mixing LiFePO4 and Li-PO?

Could be wicked methinks, if you get the balance right.

BTW I love this site

 

[Fuzzo]

Ain't it da bomb? Christchurch, eh? Jealous - it seems like 95% of everything bicycle related is down there. The only flat city in NZ.

I don't know about the battery mixing - I'm still experimenting with Pb and NiMH, but duivendyk suggested Safe has done some mix and matching with chemistries - I haven't contacted him just yet, but will as soon as I'm ready to get my hands dirty.

 

[Fuzzo]

Big Mistake

I was utterly mistaken on my current SLA setup. Not sure how that happened, I think I trusted the previous owner too much. After pulling the battery pack apart, I realized my mistake.

Where I thought I had 2 x 6V 8Ah series config, I actually have 2 x 12V 12AH series. So the bike is actually 24V, and I have 288 Wh. So the 111 Wh I was going to add with NiMHs will not double the range, it only adds 38%.

This affirms heathyoung's point that my batteries were SFA. If what I had said was true, that would have been totally correct, and my effective range would have really been less than a third of what it actually is (and my batteries would probably have died by now).

This leaves me in a pickle with my NiMH plans, because the 32 that I ordered will be sadly inadequate to the task of powering the bike, and will probably be destroyed if I attempt to drive the bike off them alone.

What to do? My original assumption was that adding batteries could be done in small steps, connecting more Wh in parallel, bit by bit (as I find them for acceptable prices). But it seems like this can't work, if duivendyk is to be trusted in his claim that you can't control the amp flow from any particular pack, and will thus always risk destroying the smaller pack. If the claim is true, it makes selection of battery packs a real pain in the neck, because they have to be configured symmetrically - each series string must have the same number of batteries of the exact same characteristics.

Which means I have to build the NiMH pack up to basically the same spec as the SLA pack. This involves around 83 batteries. I'm nervous about laying out the cash for a further 50 batteries at $3 a pop, if I don't need to. Ultimately, it won't break the bank or my heart to do so, but I'm loathe to do it if it's not necessary.

So I do need to know if duivendyk's point is correct. Are battery packs really this inflexible? Is it really impossible to upgrade your pack in anything less than entire increments of the size of the existing pack? I was hoping to do it 10 batteries at a time, just adding 12V here and there until I had enough sauce to do what I want. If it involves some fancy circuitry (I was envisaging a combination of diodes and resistors), I can do that. But only if it's actually possible.

This is not to rag on duivendyk at all. His cautionary words could be saving me a whole lot of money on destroyed batteries.

 

[woody]

Don't do it

Do the math. Li-Po or LiFePO4 is cheaper in the long term. LiFePO4 is the cheapest, but if you want performance go for Li-PO. Anything else is crazy. Sell the batteries you have bought, and buy something cheap. (long-term)

Only my opinion.

 

[Fuzzo]

It's hard math to do. Where's a good source of Li-Po batteries in NZ?

It does make a little more sense, though, when you consider the discharge rates. I could buy Li-Po packs as I need them, a 24V pack at 5Ah can easily deliver the desired current, and looks like it would cost about $150. It could power the bike by itself, and I could just add packs of that size as needed.

The NiMH won't go to waste. I'm always short of batteries.

 

[Happy Valley]

This is a great thread, but this is the introduction page. Fuzzo, a suggestion: why not "to be continued" it in electrics? Go ahead, link it, and start there where you left off.

I suggest this only to be fair. What ends up happening is new members introductions keep getting bumped.

 

[Fuzzo]

Thy will be done!