[C320-list] Battery Isolation
Robert Seastream
robert.seastream at comcast.net
Sun Apr 19 14:31:44 PDT 2009
I'll start by stating that I've been wrong before and am always open
to learning.
Now, from below:
..."I believe that discharged batteries have INCREASED (not less)
resistance."...
OK, but if so (unless I missed something), then why do discharged
batteries draw/absorb more current than fully charged batteries?
According to Ohm's law (for DC circuits), the lower the resistance,
the greater the current (charge rate) flow.
Bob Seastream
On Apr 19, 2009, at 10:55 AM, <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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