[C320-list] Battery Isolation
Jeff Church
jc387 at att.net
Sun Apr 19 13:39:21 PDT 2009
Jeff,
I was hoping you would jump in. Great explanation. I still don't get
what the techs were warning me about a rush of current from the start to
the house when the combiner closes. Maybe it was BS, or maybe I just
misunderstood them.
JeffC
catalina at thehares.com wrote:
> Hi,
>
> I'm totally with Mr. Ashley on this one. (not his resigned "go with the
> isolator" comment however :).
>
> I believe that discharged batteries have INCREASED (not less) resistance.
> That's why the voltage drops much more when you attempt to draw current out
> of discharged batteries, and why dead batteries may boil/heat up when
> attempting to charge them with too high a charging voltage. The voltage of
> a discharged battery is pretty close to the voltage of a charged battery,
> yet a dead battery's short circuit current is quite low. So what changed?
> The cell resistance had to increase! BTW, I'd love to have a battery that
> acted as Bob suggests. That would mean that a deader the battery, the more
> current it would supply! Now that'd be Cool!
>
> A damaged battery with several cells physically shorted is a very different
> electrical situation. It's kinda like trying to charge a 8 volt battery
> with an 12v charger. The charger will supply 13.8 volts and since some of
> the cells are missing (shorted), excessive current will flow and heat up
> the cells. The amount of current is strictly mathematical. If the voltage
> at the terminals is a certain level, and there is a certain internal
> resistance then X amount of current will flow. If the charger cannot
> produce that much current, then the voltage at the terminals will only rise
> to the level that satisfies the ohm's law equation.
>
> The case JeffC outlined below is interesting but maybe not drawing the
> right conclusion? For it to behave as JeffC and Bob suggest, the ACR would
> have to have to be set to an *incorrect* turn-on voltage and have a damaged
> battery.
>
> 1) So, you have a physically damaged house battery (which would be obvious
> because it would register below 10 volts)
> 2) Most likely, Your shore power charger probably won't even attempt to
> charge it since that would be dangerous. The pro-mariner and others won't
> start until the battery voltage is at least 10v or some number like that.
> Even a completely discharged (undamaged) battery reads somewhere around 10+
> volts.
> 3) And even if your shore power charger did try to charge it, *and* it was
> successful in raising the battery terminal voltage high enough to engage
> the ACR, then the only way current would flow *from* the starting battery
> back into the house battery is if the starting battery's voltage were
> HIGHER than the voltage at the house battery terminals. ie: water don't
> flow uphill. Current ONLY flows in response to a voltage differential.
>
> Just remember: An ACR isn't just a closed switch, it's a closed switch
> *only* when the voltage on the supply side is greater or equal to the
> "turn-on" voltage. You always have this "turn-on" voltage set to a number
> that's HIGHER than a charged starting battery's voltage sitting at rest.
> That's important!
>
> If the supply side (house) voltage drops below the starting battery side
> voltage, then the switch opens up. In effect, it's a one way path.
> Current only flows as a response to voltage difference.
>
> If you set this "turn-on" voltage lower than the starting battery's fully
> charged resting voltage, then you could discharge the starting battery down
> to the "turn-on" voltage but no lower.
>
> IF the house battery has more than one cell shorted, the battery charger
> will not be able to cause the voltage at the terminals to reach 13.8 volts
> (hence no ACR turn on), even if it were to try to supply 15 or 16 volts
> output.
>
> In my opinion, CR Ashley's spot on.
>
> -JeffH
>
>
>
>> -----Original Message-----
>> From: c320-list-bounces at lists.catalina320.com
>> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Jeff Church
>> Sent: Friday, April 17, 2009 7:35 PM
>> To: C320-List at Catalina320.com
>> Subject: Re: [C320-list] Battery Isolation
>>
>> Bob,
>>
>> Me too. That's why I thought as soon as the combiner closes, current from
>> both the charger and starting battery would flow through the house
>> batteries
>> until the resistance of the house bank increased.
>>
>> What would happen if there was a shorted cell in the house bank? With a
>> combiner couldn't the starting battery discharge thru the shorted house
>> battery?
>>
>> I was also told by the guys at Charles that since the discharged house
>> batteries present the least resistance, most of the bulk and absorption
>> charge will flow thru them, so the smaller starting battery will not over
>> charge.
>>
>> Jeff
>>
>>
>> Robert Seastream wrote:
>>
>>> 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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