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Author Topic:   Behavior of VSR When Batteries Charged By External Charger
gsbaker posted 11-11-2010 07:14 AM ET (US)   Profile for gsbaker   Send Email to gsbaker  
I am preparing to set up a dual battery system. This is what I have:

--single 115 Yamaha which draws 25 amperes

--BEP dual sense VSR

--BEP battery distribution cluster, House--emergency parallel--Start switches

two-bank charger, also have single bank charger

I'm curious to know if the VSR will disengage itself if the two-bank charger is charging the batteries and they both have reached the float stage? If this is the case, should I put in another switch so that the VSR is off during battery charger operation?

Or, if I just install the one-bank batt charger will the VSR work properly to maintain the two batteries?

Any comments would be appreciated.


jimh posted 11-11-2010 07:48 AM ET (US)     Profile for jimh  Send Email to jimh     
If the voltage sensitive relay operates based on the input voltage to its sense lead or sense leads, it presumably will close and parallel the batteries whenever the voltage on its sense lead or sense leads is above threshold. It cannot tell if the source of that voltage is high (that is, above threshold) due to the battery voltage itself being high, or if the battery voltage is being forced high by charging current, and, it cannot tell if the charging current is from the outboard motor or an external charger. The VSR just senses voltage and reacts accordingly. Therefore I would presume that if you apply a charging current from an external charger to each battery, the VSR will see the higher voltage on its sense lead or sense leads and react as it is programmed.
jimh posted 11-11-2010 08:37 AM ET (US)     Profile for jimh  Send Email to jimh     
If you want to suppress the VSR from operating when the above-threshold condition occurs due to an external battery charger (which operates from AC power) creating the higher voltage on the batteries, you could disable the VSR by using the following method:

--wire the coil of a relay in parallel with the AC voltage power to the external battery charger

--wire the relay contacts of the coil so that they operate to suppress the VSR from closing when AC voltage is present

I do not recall the details of the BEP VSR product, but I suspect there is some simple way to suppress it from operating. Typically if you open the circuit from the VSR to ground it cannot sense the voltage and thus cannot operate. You could route the ground lead from the VSR through the relay on the battery charger circuit.

These VSR installations can become rather complicated, which is what led me instead to a alternative solution using a dual-output alternator from my single outboard motor.

gsbaker posted 11-20-2010 05:58 AM ET (US)     Profile for gsbaker  Send Email to gsbaker     
While the dual alternator setup is nice, however, my boat will generally see light usage and sit for a long winter period. I want to (1) make sure that the batteries will be maintained by using a 3 stage charger and (2) when using the boat the motor is stopped and started very often during the course of the day.

I'm still curious about the following scenerio: A two bank battery is connencted and is charging two seperate batteries. A dual sense VSR is also connected with the battery switch cluster (switches are "OFF". Now say battery one is at full charge which triggers the charger to go into the float stage. Battery 2 is not fully charged and is in stage ONE charge mode. What will the VSR do in this scenerio?

jimh posted 11-20-2010 09:35 AM ET (US)     Profile for jimh  Send Email to jimh     
I believe I already answered that question.

The VSR is not aware of circumstances, it is only aware of voltage and time. If the voltage on its sense lead is above threshold for the required amount of time, the VSR operates to parallel the batteries.

I described the method to disable the VSR from operating when the charger is the source of the voltage. However, feel free to invent an alternative method.

jimh posted 11-20-2010 12:26 PM ET (US)     Profile for jimh  Send Email to jimh     
If using a sophisticated charger which has multiple charging strategies and completely isolated dual outputs, it seems particularly inappropriate to use a VSR to parallel the batteries while the charger is operating. I would carefully read the literature from the manufacturer of the sophisticated charger to learn his opinion on connecting the two charging circuits in parallel, which is what will occur if the VSR operates. You could damage the charger that way.

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