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Battery combination ?

2207 Views 2 Replies 2 Participants Last post by  Coley
With the weather dropping the temp a bit, the early morning ride to town has less oomph, than when it is 50 degrees or above.

My question is,

How well does it work to add more batteries in parallel to the pack for longer range.
I have room under the hood to add the 7th battery in parallel.

How well does this battery charge and discharge compared to the series wired pack?

Would it provide much of an increase in range?
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You’re asking about adding a single battery in parallel with one of the several batteries you have in a series string? One piece of advice:


First of all, it would not increase your range because in a series circuit, the current is the same everywhere. Several discharged batteries in series with two paralleled batteries would still result in lower operating voltages (read: sluggishness in cold weather)

Additionally, combining batteries in series or parallel is not recommended unless the batteries are all the same age, and have experienced similar (or identical) discharge/charge regimes. Old/new, weak/strong, dissimilar make/model battery combinations will always be a big disappointment, and will usually lead the to batteries failure in a much shorter period of time. If you wanted paralleled batteries, the time to do it would have been when the batteries were all new.

The cure for cold weather sluggishness is to put heaters under the batteries, making sure that they all operate at the same temperature. Either that, or do as most EV's do and just put up with lower performance in the winter time.

Here's a battery story for you:

When I first put a digital ampere-hour meter on my EV (Cruising Equipment E-Meter), I tapped the battery pack at 18 volts (three batteries) to get the power to run the meter. I had heard that tapping a series string of batteries was not a good idea, but I thought "How bad could it be?", since the E-Meter only drew a few hundredths of an ampere.

I soon found out, when those three batteries began to be the first to die out when the car was run more than a few miles. The E-Meter would go blank because the collective voltage of the three 6-volt batteries would drop below 9 volts. To remedy this, I tapped higher on the pack, sending the E-Meter 30 volts from five batteries. The two additional batteries died is short order as well. I ended up having to replace the five batteries when my range dropped to only four or five miles.

Now, replacing just five of 18 batteries is breaking another of the rules (batteries all same age), but the alternative was replace the entire pack (~$1,200), so I decided to fudge a bit.

The problem with tapping the pack to run a small electronic gauge was that those three (then five) batteries would be slightly more discharged than the rest of the pack after the car sat, and after driving. That tiny bit of difference meant that when the rest of the batteries were fully charged, the tapped part of the pack wasn't. The difference in service life and discharge/charge cycles meant that those three/five batteries needed a completely different charge regime that the remaining batteries in the pack that weren't supplying a small additional load. Since the traction pack was a series string, the charge current was the same for all batteries in the pack, and it was impossible to set up a separate charging regime for the three/five that needed it.

It was an expensive lesson (~$350), but one learned well. The battery pack in my car is still mismatched (older and newer batteries in series), but the difference is much less of a problem. None the less, I now have a total range of less than 15 miles, and it's time for a new pack again, one that is matched in age.

The E-Meter? I ended up powering it from the auxiliary battery through a small DC-to-DC converter that I bought from a catalog for $19. It's what I should have done from the start.

If a 30 milliampere load could kill my expensive battery pack, imagine what mismatching your pack with a paralleled single pair of batteries will do...

Leave it alone, you'll be much less unhappy than by experimenting in that manner.
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