Two battery banks in different locations

[Kettlewell]

May I humbly suggest that joking in an electrical thread might not be a good idea? It is often difficult to discern sarcasm when one is unfamiliar with the subject at hand.

[btrayfors]

Originally Posted by Kettlewell

May I humbly suggest that joking in an electrical thread might not be a good idea? It is often difficult to discern sarcasm when one is unfamiliar with the subject at hand.

Hey....I agree with you. But if ANYONE doesn't get the "house wire" joke -- except perhaps Andina Marie -- they don't deserve to be let out of the house :-)

B

[CharlieJ]

You betcha!

[sailinglegend]

Originally Posted by Andina Marie

Overkill......
...expect the local battery to be the source and just use 6 gauge wire to link to the other battery....You DON'T need 250 amps available from both batteries.

When charging, even if the alternator could sustain 100 amps, the voltage drop over a 6 gauge wire is not important because as the battery voltages increase the current drops.......

Again, a total load of rubbish from someone in the industry who should know better. This kind of ignorance would not induce me to buy any of your combiner products.

"Overkill", as you describe it, is good engineering. Something probably you don't find in Trawler Fleets! I note that you apply this "engineering knowledge" in your products - so a maximum of 6 gauge wire is allowed. Try and put 100 amps down that for any distance and the second battery will take much longer to reach a sensible voltage and charge properly - never going to happen if using your generator or engine on a sailboat. My VSR combiner can carry 300 amps and work as an emergency parallel switch!!!


Ignorance isn't what you don't know, but what you think you know that is incorrect.

[Zil]

Short jokes are not funny.

[Andina Marie]

Originally Posted by sailinglegend

Again, a total load of rubbish from someone in the industry who should know better. This kind of ignorance would not induce me to buy any of your combiner products.

"Overkill", as you describe it, is good engineering. Something probably you don't find in Trawler Fleets! I note that you apply this "engineering knowledge" in your products - so a maximum of 6 gauge wire is allowed. Try and put 100 amps down that for any distance and the second battery will take much longer to reach a sensible voltage and charge properly - never going to happen if using your generator or engine on a sailboat. My VSR combiner can carry 300 amps and work as an emergency parallel switch!!!

Emotional response is fine but do the calculations first.

You don't end up with 100 amps in the cable between the batteries. When you start charging with a 100 amp rated alternator, the batteries start out at equal voltage, equal charge.
So
1. 50% of the current is going into the first battery, only 50 amps needs to go to the second battery through the jumper.
2. A 100 amp rating alternator can only put out 100 amps when COLD, at optimum RPM, into an 11 volt load on a test bench. In the real world they put out 100 amps for a few seconds if you're lucky and the battery voltage then rises over 13 volts so the current drops. After a few minutes the temperature rises and you will be lucky to get 75 amps sustained.
3. As the voltage rises and you get into the final stages, the current will be less than 25 amps, half of which is going to be into the first battery. A 10 foot jumper of 6 gauge is 0.004 ohms so the voltage drop is 0.05 volts, 50 thousandths of a volt. Most meters on boats can't even measure to that accuracy.

By all means, spend the money on the 1/0 gauge cable if you feel better but do the calculations before you say everyone else is wrong.

[Paul Elliott]

I=E/R. It's not just a good idea, it's the law!

[sailinglegend]

Originally Posted by Andina Marie

Emotional response is fine but do the calculations first.

You don't end up with 100 amps in the cable between the batteries. When you start charging with a 100 amp rated alternator, the batteries start out at equal voltage, equal charge.
So
1. 50% of the current is going into the first battery, only 50 amps needs to go to the second battery through the jumper.

For the sake of other readers to this post lets do some calculations.

You recommend charging your starter battery first - that goes against all other professional recommendations and cause problems with combiners cutting in and out repeatedly. But that's another issue.

Equal voltage doesn't mean equal charge. It depends on the batteries ability to accept charge depending on its state of charge and capacity. If you charge your small starter battery first with a 100 amp shorepower or alternator it may well get close to full within a few minutes, so it is left with maybe only two amps going into it, not 50. So 98 amps are now trying to charge your much larger service battery 20 feet away through a 6 gauge wire!

Originally Posted by Andina Marie

2. A 100 amp rating alternator can only put out 100 amps when COLD, at optimum RPM, into an 11 volt load on a test bench. In the real world they put out 100 amps for a few seconds if you're lucky and the battery voltage then rises over 13 volts so the current drops. After a few minutes the temperature rises and you will be lucky to get 75 amps sustained.

A proper multi-stage shorepower or alternator charger will maintain a constant current for maybe an hour until the boost voltage of 14.4v is reached, then the charger becomes a constant voltage device and the current starts to fall as the battery builds up a charge.

In the real world on my boat my Balmar 100 amp marine "hot rated" alternator will happily output 90 amps into my large AGM battery bank for an hour before the battery acceptance starts to reduce the current. Going through a 6 gauge wire this would take a lot lot longer.

Originally Posted by Andina Marie

3. As the voltage rises and you get into the final stages, the current will be less than 25 amps, half of which is going to be into the first battery. A 10 foot jumper of 6 gauge is 0.004 ohms so the voltage drop is 0.05 volts, 50 thousandths of a volt. Most meters on boats can't even measure to that accuracy.

Correction to your figures:
0.05v is 5 hundredths not 5 thousandths of a volt.

The current isn't the same going into both batteries unless you are combining two batteries of the same capacity with the same depth of discharge.

So 98 amps down a 10 foot 6 gauge wire has a voltage drop of 0.4 volts. Add the voltage drop on the return 10 foot negative cable and the total drop is 0.8 volts. The greater the batteries are separated the worse the voltage drop gets. Bowthruster batteries 30 feet away would have an initial voltage drop of 2.4 volts. Your ideas make no sense.

[zboss]

Ok, everything I know says you should prepare for the worst possible outcome, which for me says using the highest grade and gauge wire necessary to move electrons from one place to another... so... 1/0. Its only 6.99 at WM so if we are only talking about 10 feet, so what. I would rather not have a fire nor starve my devices for power.

[Andina Marie]

Originally Posted by sailinglegend

For the sake of other readers to this post lets do some calculations.

You recommend charging your starter battery first - that goes against all other professional recommendations and cause problems with combiners cutting in and out repeatedly. But that's another issue.

HUH? Where did you read that? Our combiners are designed to regulate current to a safe level for the alternator. They do it by cycling on and off. Ours have been doing it for 20 years and not a single warranty claim due to failed relay contacts.

Equal voltage doesn't mean equal charge. It depends on the batteries ability to accept charge depending on its state of charge and capacity. If you charge your small starter battery first with a 100 amp shorepower or alternator it may well get close to full within a few minutes, so it is left with maybe only two amps going into it, not 50. So 98 amps are now trying to charge your much larger service battery 20 feet away through a 6 gauge wire!

Equal voltage does approximately mean equal "state" of charge, obviously a 200 amp-hour battery at 75% will have twice the capacity of a 100 amp-hour battery. Since the batteries are in parallel you cannot charge the starting battery first and then send 98 amps to the second battery. By the time the starting battery is 14.4 the distant battery will be within 0.1 volts.

A proper multi-stage shorepower or alternator charger will maintain a constant current for maybe an hour until the boost voltage of 14.4v is reached, then the charger becomes a constant voltage device and the current starts to fall as the battery builds up a charge.

In the real world on my boat my Balmar 100 amp marine "hot rated" alternator will happily output 90 amps into my large AGM battery bank for an hour before the battery acceptance starts to reduce the current. Going through a 6 gauge wire this would take a lot lot longer.

If the voltage at the end of stage one is 14.4 on the first battery and if it is STILL receiving 45 of the 90 amps, then the second battery on the 6 gauge wire will be 14.35. Since fully charged at rest is about 12.8 that is close enough for most people.

Correction to your figures:
0.05v is 5 hundredths not 5 thousandths of a volt.

Excuse ME. Go look at the original and also your quote of the original, it states 50 thousandths of a volt.

The current isn't the same going into both batteries unless you are combining two batteries of the same capacity with the same depth of discharge.

So 98 amps down a 10 foot 6 gauge wire has a voltage drop of 0.4 volts. Add the voltage drop on the return 10 foot negative cable and the total drop is 0.8 volts. The greater the batteries are separated the worse the voltage drop gets. Bowthruster batteries 30 feet away would have an initial voltage drop of 2.4 volts. Your ideas make no sense.

Now you are introducing an entirely new scenario, unrelated to the original. In the original one battery was adjacent to the charging source and was running an inverter through 1/0 cables with additional separated capacity in parallel. I'm not sure what you are quoting in regard to a bow thruster.

[Zil]

What happens to those 6 gauge wires when the inverter wants more?

[Andina Marie]

The original setup indicated that the battery adjacent to the inverter was large enough to handle the intermittent full load current.

If the primary battery was removed the inverter would not run on the secondary battery due to voltage drop in the cables.

[Zil]

Would the 6 agw cables get hot if the primary battery failed?

[barnakiel]

I would go for two separate banks: e.g. starter battery one side (the one where wires run to starter is shorter, house bank on the opposite side. Then I think as long as they are separate banks, whether start/house or house/house, there are no issues whatsoever with wherever you place them.

b.

[Andina Marie]

Originally Posted by Zil

Would the 6 agw cables get hot if the primary battery failed?

It would be very obvious to the user if the primary battery was missing. In using batteries for 50+ years I've never seen one suddenly go open circuit but I guess a connection could be left off.

Running without the primary battery and assuming the inverter would operate, would heat the cable with the equivalent of 40 to 60 watts per foot of cable. There would be no catastrophic failure.