Mixing different capacity batteries in 48v pack for Crystalyte Journey system

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dannytroy
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Mixing different capacity batteries in 48v pack for Crystalyte Journey system

I posted this question in the Bicycles forum but didn't get much of a response. Maybe someone here can offer some advice.

I'm adding a 10-cell D-size battery pack to my existing 36v Crystalyte Journey pack. The problem is I believe the original pack is 8Ah and the pack I'm adding is 10Ah batteries. Since I'm adding the pack in series I'm wondering what the downside of the mismatch will be. If this was Lithium batteries I know that would never work, since Lithium can't go below a specific voltage without damage. I'm thinking the 8Ah batteries will just become depleted sooner than the other batteries, and I suppose those batteries won't last as long. I don't know if this will be a major problem though, since most of my bike use is for short hops and I charge immediately after use.

Any ideas?

Danny

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Re: Mixing different capacity batteries in 48v pack for Crystaly

Hi Dannytroy,

Welcome to the VisforVoltage Community!

I don't know the answer to your question but I'm assuming that the D-size cells are 1.2 volts each.
In other words are you are adding a 12 volt 10Ah pack in series with an existing 36 volt 8Ah pack to make a 48 volt pack?
If so, I would think that there may be a problem with the differing voltages, not necessarily a problem with the Ah's.

I'm sure one of our electrical wizards will step up and inform us both on whether this will work or not.

Dave

MB-1-E
Electric - Bridgestone MB-1 Mountain Bike

Dave B

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<a href="http://visforvoltage.org/book-page/996-mountain-bike-conversion-24v-3-4h... - Bridgestone MB-1 Mountain Bike</a>

chas_stevenson
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Re: Mixing different capacity batteries in 48v pack for Crystaly

Dannytroy,

Mixing different AH sizes is never a good idea. This can cause the lower AH batteries to discharge further than you want. The difference in voltage is NOT a problem in a series battery configuration. If you are using a meter that can tell you how many AHs you are using as you ride, see DrainBrain, and never go past your lowest batteries capacity then there should be no problem. However if you go past the AH rating of the lowest battery you could cause the battery to reverse polarity which would cause a great amount of damage to it's ability to hold a charge.

Chas S.
My Bicycle Pages

reikiman
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Re: Mixing different capacity batteries in 48v pack for Crystaly

While the described scenario is a bad idea; it's quite reasonable to parallel batteries of different capacity, what's a bad idea is to mix battery sizes in series.

In series .. if each battery has differing capacity, then they'll run out of juice at different times, and once one of them starts to run low the others will be stressed pumping out extra juice.

For parallelizing batteries ... you wire "pairs" of batteries and then string the battery pairs in series. But I'd say in a string of paired batteries the resulting capacity of each pair should be the same, because of the above.

- David Herron, http://davidherron.com/

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dannytroy
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Re: Mixing different capacity batteries in 48v pack for Crystaly

I am very familiar with battery use when it comes to r/c airplanes, since I fly r/c and most of my r/c planes are electric. I know mixing unequal packs, whether parallel or series, when using lithium batteries is a major no-no. The nimh packs I've used in the past are much more forgiving. I've flown packs that were so depleted after a long flight, they are almost too hot to touch. Amazingly, these packs after cooling will take a full charge and continue to work as they should. Funny, nimh packs are ancient history with r/c planes, yet for the electric bikes they still are useful, especially when comparing to SLA batteries.

I'm hoping the Crystalyte pack at 8Ah was conservatively rated, and the Tenergy 10Ah packs was rated for rated for more than it's capacity, bringing the packs closer in amp hours. What I'll do is check the voltage of each pack after use. One being the 36v pack and the other the 12v pack. I don't think I'll ever take a pack so far down as to force the lower capacity to reverse polarity.

I happen to have a meter that I use with the r/c planes, called Watt's Up, that I should be able to adapt for use with the bike. Very similar to the Brain Drain you mentioned. Here's a link: http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXLMV0&P=ML

If it doesn't work out I'll be selling the 36v pack on Ebay and I'll buy another 30 of the Tenergy batteries to make a 48v 10AH pack.

Danny

dannytroy
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Re: Mixing different capacity batteries in 48v pack for Crystaly

Just an update on my progress. I installed the 10-cell 12 volt pack, adding it to the 36 volt pack. It runs great on level ground but I'm having a problem with the controller shutting down when going up a slight grade. It shuts down for 30 seconds to a minute, then it re-arms and runs fine, until the next hill.
I never experience this with the 36 volt pack. The battery LED indicator shows low voltage when this occurs. I need to figure out whether it's the new 10-cell pack causing the problem, or the controller shutting down due to over amping. Tomorrow I will install a voltmeter to see what the voltage is doing when it shuts down. Worst case scenario I'll have to upgrade to a 35 amp controller.

Danny

7/19 Update: Found the problem. I used the wrong leads on the Tenergy 12v pack. I inadvertently used the charging leads instead of the main leads. When I switched all was well and I can't get it to shut down even on the steepest hill. Took it for a 6 mile ride on mixed terrain and it was great!

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