[C320-list] Battery Isolation

Wed Apr 15 06:48:10 PDT 2009

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
>>>>
>>>>
>>>>
>>>>
>>>>       
>>>>         
>>>     
>>>       
>>
>>   
>>     
>
>
>
>   