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Old 17-05-2013, 20:20   #1
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Battery Charging Questions...

If I use an automotive trickle charger to charge the batteries, does it matter which positive and negative posts I use, or can I use any of them?

Also, I have solar panels, will they or any equipment associated with them be affected by the trickle charger?

Now that I got those out of the way, you are all free to ridicule me for being the noob I am.
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Old 17-05-2013, 20:23   #2
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Re: Battery Charging Questions...

If you have two or more batteries in parallel to build a larger battery bank it is better to put the positive and negative charging wires at opposite ends of the bank.
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Old 18-05-2013, 09:40   #3
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Re: Battery Charging Questions...

It makes no difference, especially if using a trickle charger. The differential voltages introduced by battery to battery wiring are measured in thousandths of a volt which is meaningless compared to the natural variations in battery parameters.

And in particular for charging, as the batteries approach full charge, the charging current drops to zero. Since the voltage drop in the battery cables is ohms x amps, as the amps drop to zero the voltage drop decreases to zero and they all end up at the same voltage.

Just connect wherever is most convenient. However many trickle chargers are inadequate for maintaining larger battery banks - they are often barely adequate for maintaining one battery. You would be better off with a 5 or 10 amp "smart" charger, under $100 at Walmart or elsewhere. That way if you do apply a load to the batteries, bilge pump, leave a light on, etc. the charger will kick back into charging mode to replace the lost energy, and then return to trickle mode automatically.
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Old 18-05-2013, 10:48   #4
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Re: Battery Charging Questions...

Hi A.M.

Very interesting that you say it doesn't matter where the charging leads are connected to a multi-battery system. I know your position in the marine electronics industry (have some of your gear) so have to take your recommendation seriously. However, I have read detailed articles by "marine electric experts" that went into great detail about the benefits of charging from opposite ends of the bank and how best to do so.

So is your recommendation based just on a trickle charger but would be different for a larger, bulk charger or the same no matter what?
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Old 18-05-2013, 11:34   #5
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Re: Battery Charging Questions...

It makes no difference for any size charger, as the batteries approach full charge the current from the charging source approaches zero, or very small compared to inherent differences in "identical" batteries. Do the calculations, the resistance of battery jumpers is less than 1/1000 ohm. When the current gets down to 1/10 amp the voltage differential over a jumper is 0.0001 volts. DUH!

There is the suggestion however that it can make a difference for starter load currents. At 500 amps there could be 1/2 volt difference along the jumpers so if both starter leads are at one end of the bank, the nearest battery will be taking more than an equal share of the load. This may conceivably make its life shorter although it also makes the life of the other batteries correspondingly longer so the bottom line is about break even = replace batteries one at a time or have the whole bank fail at the same time. Some may prefer the idea of having one battery share a little more of the load so the other batteries are still good when the primary one fails?

Most if these effects are small in comparison to the normal battery to battery differences in manufacturing. Battery life is frequently only partially related to its treatment and some fail prematurely while others unexplainably have extended life.

I would make the battery connections (charging and/or load) at the best PHYSICAL location and not worry too much about balancing battery to battery wiring.
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Old 18-05-2013, 11:55   #6
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Re: Battery Charging Questions...

Your other question re Solar Panels. No it will not effect them. There should be a shunt fitted anyway.
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Old 18-05-2013, 12:19   #7
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Re: Battery Charging Questions...

+1 for skipmac's recommendation for charging "across" the battery. Here is a link with a detailed discussion using real mathematics :-) : SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank
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Old 18-05-2013, 12:49   #8
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Re: Battery Charging Questions...

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Originally Posted by CharlieJ View Post
+1 for skipmac's recommendation for charging "across" the battery. Here is a link with a detailed discussion using real mathematics :-) : SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank
Yes, and real world testing as well!

Not sure why Andina challenges the wisdom and experience of practically everyone in the industry when it comes to interconnecting and balancing batteries in a multiple battery bank.

Bill
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Old 18-05-2013, 13:38   #9
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Re: Battery Charging Questions...

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Originally Posted by btrayfors View Post
Yes, and real world testing as well!

Not sure why Andina challenges the wisdom and experience of practically everyone in the industry when it comes to interconnecting and balancing batteries in a multiple battery bank.

Bill

Including nearly every battery manufacturer.....
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Old 18-05-2013, 13:58   #10
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Re: Battery Charging Questions...

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Yes, and real world testing as well!

Not sure why Andina challenges the wisdom and experience of practically everyone in the industry when it comes to interconnecting and balancing batteries in a multiple battery bank.

Bill
Because the OP specifically asked about trickle charging. In this case Andina is perfectly correct. The voltage drop caused by cable resistance is vanishingly insignificant at trickle-charge current levels.

At higher charge currents, cabling topology can be a critical factor, and this is what the vendors rightly stress. Me, I'd hook the trickle charge wires across the bank, as I would connect my main charging cables. But it doesn't really matter.

Now is the OP's application truly limited to trickle-charge current levels? I have no idea.
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Old 18-05-2013, 23:25   #11
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Re: Battery Charging Questions...

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Originally Posted by Andina Marie View Post
.....so the bottom line is about break even = replace batteries one at a time or have the whole bank fail at the same time....
Quote:
Originally Posted by Andina Marie View Post
Battery life is frequently only partially related to its treatment
Quote:
Originally Posted by Andina Marie View Post
I would make the battery connections (charging and/or load) at the best PHYSICAL location and not worry too much about balancing battery to battery wiring.
How can someone in the industry give such bad advice?
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Old 19-05-2013, 11:55   #12
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Re: Battery Charging Questions...

The mathematics is undeniable. The voltage differences from one sided wiring are negligible compared to differences in battery characteristics. When the batteries reach full charge the regulator WILL CUT BACK TO TRICKLE CHARGE. At that level all batteries will be at the same voltage within 1/1000 volt.

Even if charging stops at mid charge when the voltage difference is tenths of a volt, as soon as the charging current drops to zero, all batteries will end up at the SAME voltage. You can't put enough current in from a charging source to be significant.

As I pointed out, at starter motor current levels it is a different story.

Anchor brand premium battery jumpers are 4 gauge. For a one foot battery to battery jumper the resistance is 0.00025 ohms. With a 20 amp charger and half the current going into the first battery, the voltage drop along the cable is 2.5 thousandths of a volt. Its going to be hard to convince me that this is going to make ANY significant difference to the charging characteristics.

When it cuts back to the maintenance level, say 1/4 amp, the voltage difference on the batteries due to cable drop is 65 MILLIONTHS of a volt. Someone explain to me where the mathematics is wrong.

If you're paying attention you will see there is an equivalent voltage drop in the negative cables so the voltage differences will be twice this but still insignificant.
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Old 20-05-2013, 06:36   #13
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Andina is right and I've argued the same myself. The " industry advice " is " good practice" but its just that ' good practice" in real life resistance differences in connectors , the batteries themselves etc all make such " advice" very dubious.

The fact that there is a couple of milliohms in the difference between the two cable topologies is insignificant at most charging currents we see
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Old 20-05-2013, 06:59   #14
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Re: Battery Charging Questions...

I can't claim any expertise on this subject of battery wiring, but I would appreciate Andina and GoBoating commenting on what SmartGauge writes about this. Here's what happens when you tap one end of 4 batteries in parallel, according to SmartGauge:

Quote:
The problem is that in very low resistance circuits (as we have here) huge differences in current can be produced by tiny variations in battery voltage. I'm not going to produce the calculations here because they really are quite horrific. I actually used a PC based simulator to produce these results because it is simply too time consuming to do them by hand.
Battery internal resistance = 0.02 Ohms
Interconnecting lead resistance = 0.0015 Ohms per link
Total load on batteries = 100 amps
The bottom battery provides 35.9 amps of this.
The next battery up provides 26.2 amps.
The next battery up provides 20.4 amps.
The top battery provides 17.8 amps.
So the bottom battery provides over twice the current of the top battery.
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Old 20-05-2013, 07:08   #15
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That result is a snapshot in time , averaged out over the discharge each battery contributes roughly the same , all that happens is as the strongest battery discharges its effective input resistance rises and there it starts to contribute less , the others contribute more. Evened out , its all about the same.

This type of asymmetric discharge will happen anyway irrespective of the wiring topology, due to differences in battery impedance , condition, state of charge , sulphation, not to mention wire & connector connector resistance.

Good practice is to wire from the top to the bottom , and its useful in large load scenarios ( ie approaching 0.5 C) for charging sources is make no difference in practice.

There's a lot of mumbo jumbo amongst many good things on the smart gauge site.

Dave
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