[C320-list] Battery Isolation

[Robert Seastream]

I thought a discharged battery has an extremely low resistance, thus  
presenting a near short to any charging source.

Bob Seastream


On Apr 17, 2009, at 10:00 AM, <crashley at gte.net> wrote:

> At the risk of offending Orlando again, I'll take a crack at this.  
> When you
> turn the charger on into an open circuited or discharged house  
> battery, it
> takes a little while (several seconds) for the battery voltage to  
> climb up
> to the initial charging voltage which should be about 14.4V. This  
> delay is
> because the battery looks like a large capacitor. The ACR has a time  
> delay
> in it so when it senses that the house battery voltage is 13.5V (or  
> higher)
> the timer starts and 30 seconds or so later the relay closes. At  
> this point
> the house battery is at 14.4V and the starting battery is at 12.7V  
> (open
> circuit voltage) so it will start charging too. I think the only  
> possible
> issue here is that if the house battery is a lot larger than the  
> starter
> battery, which is normally the case, the starter battery will see a  
> longer
> "absorb" charge time than it needs, but I don't think this is a big  
> problem.
>
> Long live space junk!
>
> CR Ashley
> Rosebud C320 Hull #882
>
>
>
>
> -----Original Message-----
> From: c320-list-bounces at lists.catalina320.com
> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Jeff  
> Church
> Sent: Wednesday, April 15, 2009 10:57 AM
> To: C320-List at Catalina320.com
> Subject: Re: [C320-list] Battery Isolation
>
> Chris,
>
> Like I said, maybe I didn't totally understand what the guys at  
> Charles and
> PS (2 independent sources) told me.
>
> Why wouldn't the ACR sense 14 volts, or more, the moment that the  
> charger
> switches on? My battery monitor does. I know that there will be some  
> voltage
> drop due to the discharged house, but the charger output is
> 15 or 16 volts initially.
> .
> Jeff
>
>
>
> crashley at gte.net wrote:
>> I disagree. It doesn't surprise me that the guys who make the
>> expensive MOSFET devices will tell you what they did. The ACR will  
>> not
>> close until the battery being charged reaches 13.5V. The starter
>> battery should be sitting at around 12.7V before that so it will not
>> discharge into the higher voltage battery, it will actually start
>> receiving charge current as well. I agree that the ACR will allow
>> current to go in either direction, but in this case it should not.  
>> The
>> only time this might occur is if the charging source goes away in
>> which case the ACR will open when the house battery drops to 12.7V,  
>> so
>> it should not allow the starter battery to discharge too much into  
>> the
> house battery since 12.7V is a fully charged state for lead acid  
> batteries.
>>
>>
>> PS: I am an EE and have been designing battery chargers and
>> dischargers for spacecraft for 28 years. Talk about $$$$!
>>
>> CR Ashley
>> Rosebud C320 Hull #882
>>
>>
>> -----Original Message-----
>> From: c320-list-bounces at lists.catalina320.com
>> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Jeff
>> Church
>> Sent: Tuesday, April 14, 2009 10:53 PM
>> To: C320-List at Catalina320.com
>> Subject: Re: [C320-list] Battery Isolation
>>
>> When I was designing my setup I spoke at length to several engineers.
>> The techs at Charles and Perfect Switch (PS makes MOSFET isolators
>> ($$$$) for the military and NASA) told me about this particular  
>> problem.
>>
>> My understanding is that when the charger comes ON, the ACR senses  
>> the
>> voltage and the switch closes. At that point current flows from any
>> available source towards the path of least resistance. In this case
>> the house batteries are the path of least resistance and current will
>> flow from both the charger and the starting battery to the house
>> batteries until the resistance in the house and starting batteries
> equalizes.
>>
>> An isolator does not allow any current to pass from one battery bank
>> to the other.
>>
>> I'm not an EE so maybe I got it wrong.
>>
>> JeffC
>>
>>
>>
>> crashley at gte.net wrote:
>>
>>> JeffC,
>>>
>>> The Blue Sea Systems battery combiner relay (ACR 7600) has a voltage
>>> sensor so it will not close until the house battery is being charged
>>> at 13.5V so the starter battery should never discharge into the  
>>> house
>>>
>> battery.
>>
>>> CR Ashley
>>> Rosebud C320 Hull #882
>>>
>>>
>>> -----Original Message-----
>>> From: c320-list-bounces at lists.catalina320.com
>>> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Jeff
>>> Church
>>> Sent: Wednesday, April 08, 2009 5:59 PM
>>> To: C320-List at Catalina320.com
>>> Subject: Re: [C320-list] Battery Isolation
>>>
>>> Good info. I looked all over for a Schottky diode isolator and  
>>> didn't
>>> find out that Guest made one. It also didn't occur to me that
>>> relay-type devices could create RF noise. I just found the Guest  
>>> unit
>>> (#2530) at Pyacht.com for about $140.
>>>
>>> I recently installed a Sure Power Schottky-diode isolator when I
>>> installed a starting battery on my 387. According to several  
>>> sources,
>>> using an isolator is a better approach than using any of the
>>> combiners or other relay-type devices. The biggest problem with a
>>> combiner/relay is that when the charging device initially starts and
>>> the combiner closes, the depleted house bank can immediately draw a
>>> lot of current from the  starting battery. Some of the devices like
>>> the Echo Charger might not operate that way, but you should check on
>>> that before buying one. The advantage of the combiner is that it is
>>> easier to install and
>>>
>> less wire ($$) is required.
>>
>>> In order to install an isolator you will need to remove the wire  
>>> that
>>> connects the alternator to the starter motor, and run a #6 wire from
>>> the alternator to the input terminal on the isolator. Then from the
>>> #1 and
>>> #2 output terminals on the isolator you run wires to the battery
>>> switch
>>> #1 and #2 terminals, or directly to the house and starting  
>>> batteries.
>>>
>>> Good luck.
>>>
>>> JeffC
>>>
>>>
>>>
>>> jelliott at landspring.net wrote:
>>>
>>>
>>>> I'm learning more... These are relay-based devices; Blue Sea tech
>>>> support says they may induce RF noise if installed at the panel vs.
>>>> at the battery (not desirable in my case).  Have you experienced  
>>>> this?
>>>>
>>>> The Guest isolators use Schottkey diodes, which induce a load (and
>>>> corresponding heat), but don't suffer the potential RF problem.
>>>>
>>>> As usual, there is a tradeoff...
>>>>
>>>> Julian
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>> The Yandina is the one I used (mine is a WM re-label of this
>>>>> product.) It's as simple as described. The Blue Seas Relay will
>>>>> definitely do the trick as well...
>>>>>
>>>>> Regards,
>>>>>
>>>>> Jon Vez
>>>>> Solstice #582
>>>>>
>>>>> -----Original Message-----
>>>>> From: c320-list-bounces at lists.catalina320.com
>>>>> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of
>>>>> jelliott at landspring.net
>>>>> Sent: Wednesday, April 08, 2009 4:09 PM
>>>>> To: C320-List at Catalina320.com
>>>>> Subject: Re: [C320-list] Battery Isolation
>>>>>
>>>>> John,
>>>>>
>>>>> I see WM has a Blue Sea Systems Starting Isolation Charging Relay
>>>>> which seems to do the trick.  Is that what you installed?
>>>>>
>>>>> Also seen similar items from Guest and from a company called
>>>>> Yandina (http://www.yandina.com/NewCatalog.htm).
>>>>>
>>>>> Looks like this fits the bill with a fairly straightforward
>>>>>
>> installation.
>>
>>>>> Almost too simple to be real...
>>>>>
>>>>> Julian
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> Julian,
>>>>>>
>>>>>> I have the exact setup you describe. I used a battery combiner
>>>>>> from West Marine. It's a simple device that you simply wire to
>>>>>> each pole on the back of your current switch--one wire to the '1'
>>>>>> and the other to the '2'.
>>>>>> It's
>>>>>> about the size of a match box and takes a couple of minutes to
> install.
>>>>>> It
>>>>>> will combine the batteries when motoring via the alternator and
>>>>>> isolate them when not receiving a charge. Is the 'easy' solution
>>>>>> to this problem....
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Jon Vez
>>>>>> Solstice #582
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: c320-list-bounces at lists.catalina320.com
>>>>>> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of
>>>>>> jelliott at landspring.net
>>>>>> Sent: Wednesday, April 08, 2009 10:59 AM
>>>>>> To: C320-List at catalina320.com
>>>>>> Subject: [C320-list] Battery Isolation
>>>>>>
>>>>>> I am in the process of modifying my electrical system, and am
>>>>>> curious as to how others electrically isolate the house bank from
>>>>>> the starting battery.
>>>>>>
>>>>>> I have two 4D's under the settee paralleled as my house bank, and
>>>>>> a separate  starting battery located in the port lazarrette.   
>>>>>> Both are
>>>>>> connected to independent channels of a Xantrax Truecharge 20.    
>>>>>> The
>>>>>> house
>>>>>> bank is monitored with a Link 10.
>>>>>>
>>>>>> The banks are still not electrically isolated; I assume this is a
>>>>>> result of a common connection to the alternator?  How do others
>>>>>> handled
>>>>>>
>>>>>>
>>> this?
>>>
>>>
>>>>>> I
>>>>>> understand there are battery isolators that do this?  Any advice
>>>>>> on how to "break" this return circuit (if that's the cause) would
>>>>>> be appreciated.
>>>>>> I
>>>>>> am not very interested in adding a second switch which I know  
>>>>>> some
>>>>>> have done.
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Julian
>>>>>> Polaris #340
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
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