About to buy an AGM battery bank. Anything new or economical I should consider?

[Falsa_Nominis]

Your point being ?
A massive parallel bank (3 strings) containing series batteries (6v x 2)

The point is: Even with the best of engineering, one cannot factor out manufacturing variations. In a parallel array of batteries there is going be some imbalance because of manufacturing variations in the cells that compose a battery. For this reason, if one can do a one series string battery bank, one would be better off doing a one series string battery bank instead of a parallel battery bank. A one series string battery bank produces the longest life span and the lowest required maintenance ... better ROI and lower overhead.

[Withalligators]

For my last series bank, I used 2/0 cable, with copper terminals that I crimped at West Marine, soldered afterwards, and then used heat shrink tubing on to cover as much as possible. Is that enough?

Oh, I've been wondering this, can the cables connecting the batteries in series be different lengths?

[Falsa_Nominis]

Oh, I've been wondering this, can the cables connecting the batteries in series be different lengths?

It depends. If the cable lengths are symmetrical from the midpoint to both end points, It will be OK. If the cable lengths are asymmetrical from the midpoint to both end points, there will be a voltage imbalance across the batteries. Keep it as symmetrical as possible and the shortest possible lengths best results.

[sdold]

It depends. If the cable lengths are symmetrical from the midpoint to both end points, It will be OK. If the cable lengths are asymmetrical from the midpoint to both end points, there will be a voltage imbalance across the batteries. Keep it as symmetrical as possible and the shortest possible lengths best results.

Why would it matter? The current is the same in all batteries in a series string.

[jflorey2]

It depends. If the cable lengths are symmetrical from the midpoint to both end points, It will be OK. If the cable lengths are asymmetrical from the midpoint to both end points, there will be a voltage imbalance across the batteries. Keep it as symmetrical as possible and the shortest possible lengths best results.

Nope. Cable lengths don't matter in series batteries (provided they are adequately sized to handle the current at that length, of course.)

[Sunking]

Oh, I've been wondering this, can the cables connecting the batteries in series be different lengths?

No problem at all providing the cable size is adequate. You wil most likely be using over sized cable, so nothing to worry about.

[Sunking]

It depends. If the cable lengths are symmetrical from the midpoint to both end points, It will be OK.

Do not listen to this idiot. He s as dumb as a rock giving bad and dangerous advice.

Mods nuke this SOB before he gets someone hurt.

[Falsa_Nominis]

Why would it matter? The current is the same in all batteries in a series string.

It is not a technical issue with series battery banks, it is a best educational issue and a it is a preempt.

Many people will undersize the battery bank because they do not develop an energy usage profile before building the system. By the time they realize the mistake, they will be economically locked into a battery bank voltage. Their only economical option will be to expand the battery bank by going to a series-parallel battery bank.

Over the years I have tried to get people to develop energy usage profiles before building but the success rate is not very good. Many either cannot do the math or they choose to follow somebody else that does not understand the value of an energy usage profile.

By teaching people to be uniform with series interconnect cables, I am teaching them a practice that can benefit them later.

If others choose to teach sloppy wiring practices and deal with the fall out later, that is their decision and they can deal with the fallout.

[Mike90250]

It depends. If the cable lengths are symmetrical from the midpoint to both end points, It will be OK. If the cable lengths are asymmetrical from the midpoint to both end points, there will be a voltage imbalance across the batteries. Keep it as symmetrical as possible and the shortest possible lengths best results.

You get another vacation to learn how a series circuit works. Don't rely on you-tube idiots to teach you.
Continue giving erroneous information, and you get longer vacations.

[Mike90250]

For my last series bank, I used 2/0 cable, with copper terminals that I crimped at West Marine, soldered afterwards, and then used heat shrink tubing on to cover as much as possible. Is that enough?

It's overkill. Soldering is harmful, because it
a) wicks solder up the cable in an uncontrolled manner
b) the heat of soldering damages the insulation
c) a properly crimped connector is gas tight, and has no room between the strands to wick solder into the joint
d) if a connector relies on solder, under high amps, the solder can melt and let the wire fall out

Oh, I've been wondering this, can the cables connecting the batteries in series be different lengths?

In series, all current is equal at all points, excess length just means a bit more total resistance in the circuit

[Withalligators]

Excellent info. Thanks! You guys are super helpful and I appreciate it.

[Sunking]

For my last series bank, I used 2/0 cable, with copper terminals that I crimped at West Marine, soldered afterwards, and then used heat shrink tubing on to cover as much as possible. Is that enough?

OK I just caught this after Mike pointed it out. I do not take any issue with over sizing if some conditions are met which I will get to next. What I have a big problem with is SOLDER. Time to ge ton my soapbox. For Pete's Sake and yous personal safety do not ever do that again. This is not an opinion, professional fact. A lot of property has been destroyed and many people have died from soldered connections. There is a good reason the FAA (aerospace), SAE (automotive), and USCG & ABYC (Marine) industries forbid the use of solder, and NEC severely restricts it use to state can only be used if the connection mechanical and electrical connection does not depend on solder. Short story it solder is weak and a poor conductor.

Stick with properly compressed compression terminals using approved tooling and terminals. A properly terminated terminal is stronger the the wire it is connected to and the extreme pressures homogenize the conductors effectively weld them electrically for the lowest resistance possible. So I have no issue over sizing cables. But with any of them larger than 6 AWG, have a Marine, Cable Shop, electrician, or buy terminated cables. Consumers just do not have the tooling and experience.

OK off my soap box.

What I do suggest for all RV users out there is use Marine Rated Cable and Devices. To size your wiring needs use the following table 3% column. Example if you have a 50 amp fuse and 1-way distance will require 4 AWG.

[jflorey2]

It is not a technical issue with series battery banks . . . . .

So to sum up - your claim that "If the cable lengths are asymmetrical from the midpoint to both end points, there will be a voltage imbalance across the batteries" in series strings is incorrect.

Good, now that that's out of the way -

If others choose to teach sloppy wiring practices and deal with the fall out later, that is their decision and they can deal with the fallout.

Using non-equal-length wiring for series strings is not a "sloppy wiring practice." Indeed, if going to unequal length wiring in such cases minimizes total cable length, that would be considered best practice.

[Sunking]

Using non-equal-length wiring for series strings is not a "sloppy wiring practice." Indeed, if going to unequal length wiring in such cases minimizes total cable length, that would be considered best practice.

Allow me to pile on so he is so discredited and embarrassed he never comes back.

You got it backwards. Non equal lengths compounds the problem for PARALLEL batteries you idiot. You are on my radar and a target. You are also on the moderators radar and other engineers ready to attack you. Understand? Now go away.

[Withalligators]

Copy that. Never solder terminals again. What about the inter-cell cables, what gauge should I use? I can probably order premade ones, right?