Charging Batteries with Perko Switch

caken

Seaman
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Oct 14, 2008
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64
Hey Everyone!

So I understand how the Perko switch works and is wired but I have a question about how the alternator charges the batteries.

I get that on position 1 it charges battery 1 and position 2 charges battery 2 but my confusion comes in when it is set to all. Obviously both batteries are being charged but how does the charging work when one battery is depleted almost all the way (deep cycle) and the other (starting battery) may be at 75% or so from starting the boat. Does the alternator continue to put out juice until both batteries are at 100%? Or does the depleted battery take the charge faster since there is less resistance.

Any insight into how this works would be very appreciated!
 

Home Cookin'

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Re: Charging Batteries with Perko Switch

it's my understanding that you don't want to charge two at a time; the explanation made sense at the time; I forgot the why and just remembered the what.
 

QC

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Re: Charging Batteries with Perko Switch

This thread will be fun :facepalm: :pop2:
 

UncleWillie

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Re: Charging Batteries with Perko Switch

... Does the alternator continue to put out juice until both batteries are at 100%? Or does the depleted battery take the charge faster since there is less resistance...

You pretty much have it correct.

Consider if the alternator were not running.
The more charged battery wold attempt to charge the less charged battery much like the situation when using jumper cables to start a vehicle with a dead battery.

With the alternator producing... for the sake of example 15 volts...
The more charged battery will take a portion of the charge current until it's internally reached 15 volts.
At this point it will just float at the alternator's voltage as it would if the other battery were not present.

The Least charged battery would take the majority of the charge current until it's internal voltage reached 15 volts.
At this point it would also float at the alternator's voltage as it would if the other battery were not present.

In the event that the alternator was not able to generate enough current to maintain regulation and the alternator's voltage were to drop below the internal voltage of the battery with the greater charge;
The More charge battery would begin discharging into the electrical system in an attempt to assist the alternator in charging the least charged battery.
In reality this situation would only occur if the alternators output were marginal for the electrical system and the situation would only continue until the battery's internal voltage matched the alternators output voltage.
A few minutes later both batteries would be in charge mode as if the other battery did not exist.

Connecting the batteries together while the engine is running to charge both batteries at the same time is exactly what an Automatic Charge Relay is for.


Yep!
This thread will be fun :facepalm: :pop2:
 

smokeonthewater

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Re: Charging Batteries with Perko Switch

also, don't look at it as cramming xx amps into the batts.... the alternator has xx amps available to maintain say 14.6 volts... the batts will each take whatever amperage is needed to reach 14.6 volts... if one really big batt was able to take more amperage than the alt could provide at 14.6 volts then the voltage would fall but otherwise each will simply absorb at whatever rate it's own internal resistance will allow

so yes the lower batt (assuming same size) would take more "juice" than the other and they would eventually both level off at full charge
 

caken

Seaman
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Re: Charging Batteries with Perko Switch

That's exactly what I thought would happen. I just wanted to make sure I understood it correctly.

Thanks everyone!
 

caken

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Re: Charging Batteries with Perko Switch

Ok, one other question. If battery 2 is depleted would you recommend starting with 1 and then running on only 2 to charge that one before combining to all? I am just curious if having it on all with 1 charged battery and the other fully depleted would put strain on the charged starting battery.
 

wrench 3

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Re: Charging Batteries with Perko Switch

Ok, one other question. If battery 2 is depleted would you recommend starting with 1 and then running on only 2 to charge that one before combining to all? I am just curious if having it on all with 1 charged battery and the other fully depleted would put strain on the charged starting battery.
You would be better to charge with the switch on both. If the depleted battery is drawing excessive current it would be harder on the alternator than the other battery. Having the other battery in the loop would even things out somewhat.
 

smokeonthewater

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Re: Charging Batteries with Perko Switch

well, "what I recommend" would be to install an acr or isolator and leave the switch in position 1 (starting batt) at all times unless your starting batt fails and you need to start off of house batt(s)... otherwise... no it won't "strain" the batt but the engine would likely start better with one fully charged batt than with one charged and one dead
 

caken

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Re: Charging Batteries with Perko Switch

LOL My thoughts EXACTLY!!

Hey guys, I'm just trying to get a better understanding of how it works. I understand batteries and electrical but I never had a full understanding of charging. I have done my research and looked all over for this answer and did not find a forum that answered exactly the questions I was looking for. It was my understanding that these forums were a place to find out information from people that did know and not be judged by them. Guess I was wrong.
 

UncleWillie

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Re: Charging Batteries with Perko Switch

It would not be a bad idea to run for 5-10 minutes on the weak battery only, before switching to Both.
It is not going to hurt the stronger battery as much as dumping an unmanageable charge in to the weak battery.
Most batteries will output 50 amps without much fuss.
Very few batteries will be able to take a 50 amp charge without boiling over.
As soon as the weak battery reaches 12.7 volts; switch to Both.

That said, if you have run the battery down below 11.9 volts often, it is going to kill the battery quickly.
 

wrench 3

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Re: Charging Batteries with Perko Switch

It would not be a bad idea to run for 5-10 minutes on the weak battery only, before switching to Both.
It is not going to hurt the stronger battery as much as dumping an unmanageable charge in to the weak battery.
Most batteries will output 50 amps without much fuss.
Very few batteries will be able to take a 50 amp charge without boiling over.
As soon as the weak battery reaches 12.7 volts; switch to Both.
I'm afraid I'm at odds with this one. An extremely flat battery will take very little charge at first, and the volt meter will be reading charging voltage (13.5-14.5) with the engine running.
BTW cakan this kind of banter is why "this is going to be fun" not a reflection on your question.
 

cayman drew

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Re: Charging Batteries with Perko Switch

Caken, you may want to consider adding a BEP VSR? They are on amazon for $73. My new boat came with one and I really like it plus the voltage sensitive battery switch just detects which battery has more voltage and starts from that. It's a neat system and not much money to replace the older Perko's with.

AVA_2725_zpsab9fd619.jpg


Here's some info from their website and check out the wire diagrams as well. Good stuff to learn.

The Voltage Sensitive Relay (VSR) allows two batteries to be charged at the same time. When the engine is started and the start battery reaches 13.7 volts, the VSR engages, allowing two battery banks (start and house) to be charged simultaneously. When the voltage drops below 12.8 volts (eg the engine is stopped), the VSR disengages, separating the batteries. This system eliminates the possibility of draining the start battery and protects sensitive electronic equipment powered from the house battery from harmful engine start up spikes.

DVSR:

http://www.bepmarine.com/home-mainmenu-8/product-714/digital-voltage-sensing-relay-dvsr

Voltage sensitive battery switch:

http://www.bepmarine.com/home-mainmenu-8/productcategory-240/voltage-sensitive-battery-switch
 

UncleWillie

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Re: Charging Batteries with Perko Switch

I'm afraid I'm at odds with this one. An extremely flat battery will take very little charge at first, and the volt meter will be reading charging voltage (13.5-14.5) with the engine running.
BTW cakan this kind of banter is why "this is going to be fun" not a reflection on your question.

Well, I am with you on this one! :)
I am not quite sure what part you are disagreeing with.:confused:

The extremely flat battery will indicate above 13 volts in short order.
My 5-10 minutes estimate was very pessimistic, if the dead battery didn't show 13 volts in a few minutes, it likely never would.
At that point(13v+), going to BOTH would not have the better battery discharging.


-----------
I was disappointed that a good discussion had not developed in this thread.
Now it is getting Fun! :pop2:
 

QC

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Mar 22, 2005
Messages
22,783
Re: Charging Batteries with Perko Switch

It was my understanding that these forums were a place to find out information from people that did know and not be judged by them. Guess I was wrong.
BTW caken this kind of banter is why "this is going to be fun" not a reflection on your question.
Yeah, I started it :facepalm: We just know from experience that this is almost like an oil thread. No shortage of opinions and we often end up confusing the guy who asked. Nothing about you at all. Sorry it looked less than polite :redface:
 

hungupthespikes

Master Chief Petty Officer
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Sep 25, 2009
Messages
814
Re: Charging Batteries with Perko Switch

S8861's link nails it. If the second battery is low the first battery will charge it as fast as the two will allow and there is a potential for heat and burning wires. It's best to charge each separately then go to both if you want.

I seldom run both, start and charge the starting battery then go to the house before we get to our destination. Run the house battery then start on the starting battery then after the starting battery is charged, switch to charge the house back up.
You end up with both batteries to there fullest and not a common voltage. Always keeping a full and separated starting battery for peace of mind.

BEP VSR looks like the way to go. thanks for the info cayman drew
huts
 

caken

Seaman
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Oct 14, 2008
Messages
64
Re: Charging Batteries with Perko Switch

Yeah, I started it :facepalm: We just know from experience that this is almost like an oil thread. No shortage of opinions and we often end up confusing the guy who asked. Nothing about you at all. Sorry it looked less than polite :redface:

Haha, ok. I guess this is why I have had such a hard time finding the answer to my question. All the different threads have so many different answers it was hard to figure it out.
 

Outsider

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Apr 24, 2007
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1,022
Re: Charging Batteries with Perko Switch

I use two identical AGM batteries, but only run on one for any given day. The whole shebang, electronics and all. Should I deplete that battery (once on 15 years), I'll switch to the other one and head for home. I'm just not going to keep running around out of sight of land with only one good battery. If I have a lengthy run home, I might switch to the depleted battery for the run, then recharge fully when I get in and have figured out why it went flat. I also consider BOTH to be a last resort emergency procedure. Works for me ... :)
 
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