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Old 22-06-2015, 15:57   #31
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Re: Battery Charge Alarm

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Originally Posted by hellosailor View Post
"Some batteries manufacturers state that they require 14.8 volts. "
I'd love to see a link to anything like that from any battery company, because I never have. Fifteen volts for equalizing, sometimes. 14.8 as a maximum the battery can tolerate, sometimes. But 14.8 as being necessary in normal operation? Or proper for any normal alternator power source? Never have seen it, from a battery or alternator data sheet.


Standard 15-volt electronic components, rated +-10%, are only good for service in systems running 13.5 volts, so some manufacturers are pushing the envelope just with "normal" use. (Even some of Icom's radios.)


As to the system voltage versus the starting battery voltage...we just don't know where the isolator(s) are, or where anything else has been connected, for certain. We DO know the alternator is putting out high voltage, and that if that has been improperly connected in one place...one has to suspect the possibility it is getting to other places.


Here, we know there is at least one failure in a system. Considering how frail electronics can be, it can be worth being suspicious. And worth ensuring excess voltage just isn't anywhere IN the system. If a second diode failed in short mode instead of open mode, the way the one to the starting battery apparently has? Not good. And the odds are that both diodes came off the same batch, same line, same engineering for the installation.


As the man said to Inspector Clouseau: Ah, but that's not my dog.
I don't trust sparky things, even when they are behaving.
Fact is this morning when I checked the system with the multimeter the highest voltage I saw at the battery terminals was 14.4v on the starter battery and 14.2v on the house battery. That is regardless of what was physically being put out at the time by the alternator.

During the last 4 years with an external battery monitor on the house battery I have never seen any more that 14.4v on the house side even with mains and solar panel charging.

it is purely in the last week that we have started to see 15v on the starter battery side and during this period have never seen more than 14.4v on the house battery (in fact I don't think we even saw that high).

So can I ask you to stick to the question in point which is why I am suddenly seeing such a high voltage on my starter battery and not go off tangent on what battery manufactures may or may not claim or what electronics may or may not be able to take. My domestic side is working perfectly it is only the starter side that is giving any problems and my fridge, radio, windlass, chartplotter and lights are not connected to my starter in any way shape or form.

Keiron
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Old 22-06-2015, 16:01   #32
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Re: Battery Charge Alarm

Quote:
Originally Posted by hellosailor View Post
"Some batteries manufacturers state that they require 14.8 volts. "
I'd love to see a link to anything like that from any battery company, because I never have. Fifteen volts for equalizing, sometimes. 14.8 as a maximum the battery can tolerate, sometimes. But 14.8 as being necessary in normal operation? Or proper for any normal alternator power source? Never have seen it, from a battery or alternator data sheet.
Now you have. From Trojan battery company.
Battery Maintenance | Trojan Battery Company
Quote:
Avoid charging at temperatures above 120° F (48.8° C).

Table 2
Charger Voltage Settings for Flooded Batteries System Voltage
Charger Voltage Setting 6v 12v 24v 36v 48v
Daily Charge 7.4 14.8 29.6 44.4 59.2
Float 6.6 13.2 26.4 39.6 52.8
Equalize 7.8 15.5 31.0 46.5 62.0
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Old 23-06-2015, 08:52   #33
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Re: Battery Charge Alarm

Maybe take a look at :
Sterling ProsplitR - simple swap out for your isolator
or
Merlin Smart Gauge and Smart Bank

Just some ideas ......


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Old 23-06-2015, 10:23   #34
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Re: Battery Charge Alarm

Getting back to the thread subject, the most likely problem you are having is that the start battery leg of the old diode splitter has started to short at high temperature, letting the full alternator voltage reach the start battery.

If you swap terminals on the splitter, the shorted leg should be on the house battery, which is OK because the regulator sense wire is on that side--if the diode shorts, the regulator will just reduce the alternator voltage.

You can also check out the splitter when the start battery is overcharging by measuring the voltage drop from the alternator terminal to each of the battery terminals at the splitter when the engine is running. If one is 0.6-7 volts and one is a lot less, then you have found your problem.

There is likely nothing wrong with your alternator, regulator, or batteries. There is nothing wrong with just buying and installing a new diode splitter, but I would go with one which is at least 160 amp rating, or rated for a minimum of 120 amps on EACH leg. You can also buy a 3-way splitter and get rid of the separate one for the thruster battery.

I think I have embedded a graph of volts vs amps on a typical silicon diode, and you can see just how sharp the knee in the forward curve is at 0.6v. There is no way that a working diode splitter is going to overcharge the start battery.
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Old 23-06-2015, 14:51   #35
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Re: Battery Charge Alarm

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Originally Posted by donradcliffe View Post
There is no way that a working diode splitter is going to overcharge the start battery.
If the battery being sensed has a voltage drop in its wiring the regulator will compensate for that, on top of the .6V, and overcharging of the start battery, even with a .6V drop, can happen. Lots of alternator circuits are under wired so when you sense at the battery terminals the alternator regulator has a lot to compensate for....
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Old 23-06-2015, 15:00   #36
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Re: Battery Charge Alarm

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Originally Posted by DeepFrz View Post
Now you have. From Trojan battery company.
Battery Maintenance | Trojan Battery Company
Yes, Trojan has been recommending 14.8V absorption for many years. It is what ours are charged at and they seem to like it and don't require frequent watering at all.

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Old 23-06-2015, 15:01   #37
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Re: Battery Charge Alarm

Kieron-
OK, focusing in tightly...If the voltage at both batteries is "normal" (i.e. 14.2-14.4) at some times, and the two batteries each feed off a higher voltage source through a splitter.
Rashly assuming the splitter is perhaps a 0.5V drop so the source has been adjusted or compensated for that and is provided some 15 volts, and that the voltage sense lead has either been tied back ("one-wire" configuration) or tied to the house battery alone.
Then an intermittent short of one of the isolation diodes, the one between the starting battery and the source, would explain everything. One diode shorting out is usually not an intermittent problem. So then, something could be chafed or otherwise physically bridging past that one diode and effectively shorting it out. If the diodes are physically secured and clear of metal objects, that's also unlikely. If the diodes are "hanging in space" or in a cluttered area, it becomes possible.


Don's idea of a thermal factor (something heats up, expands, shorts out that one diode) is an interesting one which would explain things nicely. Stranger things have happened.
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Old 23-06-2015, 15:15   #38
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OT: Trojan

DeepFrz-
We'll see what more they have to say. 14.8 is practically an equalization charge. This may apply only to their chemistry and construction, or it may be "pseudo-equalization" aimed at long term results.


Fast reply from Trojan"
"The “Bulk’ charge voltage has been 14.8V and our “Absorption” voltage range of 14.1V to 14.7V, which put the median at 14.4V. it has always been known that the Trojan deep cycle battery charges up better at the higher voltage setting."


Their advice appears limited very specifically to Trojan batteries, implying that there is something peculiar to their construction or chemistry, and that this advice should be constrained to their own products.
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Old 23-06-2015, 15:55   #39
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Re: Battery Charge Alarm

Interestingly it has been very warm in Croatia the past few weeks with shade temperatures into the 30ēCs. Our engine bay is fitted with an extraction blower fan to help air flow (as per the RCD) which should help keep temperatures down but it's not beyond the realms of possibility that Don's idea that it is a heat stress related diode short could be correct.

As far as I can tell there is nothing forming a short circuit across the terminals of the isolator and all the wires are secure and in good condition. I've checked all the connections and cables for any signs of damage and all appears to be in good shape.

Currently at work so can't check anything on the boat until I get back and I am having a look into the Sterling Prosplit R and Merlin Smart Bank as suggest by Damian as an out and out swap for the isolators we have. Any other suggestions welcomed.

Cheers

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Old 23-06-2015, 17:45   #40
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Re: OT: Trojan

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Their advice appears limited very specifically to Trojan batteries, implying that there is something peculiar to their construction or chemistry, and that this advice should be constrained to their own products.
I have always understood it this way.

East Penn recommendations are for charging at 0.33C until a particular specific gravity is reached. They don't recommend a particular voltage - only mentioning that the voltage should be limited to no more than 16V to reach the above conditions.

Similarly, I believe Lifeline recommends a higher voltage for their batteries than other AGM manufacturers.

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Old 23-06-2015, 18:59   #41
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Re: Battery Charge Alarm

"East Penn recommendations are for charging at 0.33C until a particular specific gravity is reached. "
ROFLMAO. And that can easily be done by any commodity-grade automatic charger that has the usual temperature compensated specific gravity sensors to add into each cell of every battery.
Next they'll void the warranty if you don't have a qualified quantum physicist monitoring the true quantum charge state of the plates as well as the purity of the electrons moving through the cables and into the batteries.

Apologies to k, the OT would be nice to split off (mods?) hope his weather cools down and the problem goes away.
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Old 23-06-2015, 19:40   #42
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Re: Battery Charge Alarm

I doubt temperature is a factor. A silicon diode forward drop changes only about -2mV per degree C. A 15 degree C change in temperature would reduce the alternator voltage by only 0.03V.

A more likely cause is something simple like a loose or intermittent wire somewhere (possibly exacerbated by temperature). Maybe in poking around checking things it has been fixed at least for now. The reported symptom indicates that the path between the alternator output and the "pink" regulator feedback wire has significant voltage drop. This high voltage drop causes the regulator to increase its output voltage. This voltage shows up on the start battery via the diode isolator because the start battery is not accepting current.
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Old 24-06-2015, 05:54   #43
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Re: Battery Charge Alarm

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Originally Posted by transmitterdan View Post
The reported symptom indicates that the path between the alternator output and the "pink" regulator feedback wire has significant voltage drop. This high voltage drop causes the regulator to increase its output voltage. This voltage shows up on the start battery via the diode isolator because the start battery is not accepting current.
I drew this a while ago for a customer who had toasted two AGM start batteries in three years. He was having trouble grasping the problem that was occurring even after showing him the voltage drop.. I summed all the VD to the positive to simplify but it made the point clearer to him. The diode isolator was replaced with a Blue Sea ACR and that start battery is now 4 or 5 years old and is in good working order.

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Old 24-06-2015, 06:45   #44
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Re: Battery Charge Alarm

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the battery alarm on the VolvoPenta panel that sounds and according to the manual "The charging lamp lights up when the alternator stops charging the batteries, which may result from a fault in the electrical system or the need to tension the alternator drive belt."
Keiron
I understand the issue illustrated above (great explanation) - but why would that set off the 'charge alarm' on the engine panel ? If the alternator is sensing the House Bank.
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Old 24-06-2015, 09:33   #45
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Re: Battery Charge Alarm

Excellent diagram Maine Sail which is almost exactly how my system is wired up, with the minor difference being the regulator is not separate from the alternator but that's just a minor difference.

it certainly helps to visualise the way the system currently works and to explain how this can occur so thank you for sharing.

Damian, the only explanation I can come up with for the alarm sounding when the starter battery hits 15+v given the regulator is sensing the house battery is the alarm must be sensing the system from somewhere else. I'm pretty certain the volt read out in my switch panel is reading from somewhere other than the batteries as it is constantly 0.2-0.3v higher than the multimeter on the studs or the external battery monitor on my house battery. I guess that could be voltage drop along wires again.

I'm really grateful for all the help, advice and feedback on this. Picking the collective grey matter has been a learning curve and I now understand electrickery a little better. Rest assured the diode isolator is going and will be replaced by something better - just not sure what yet

Cheers

Keiron
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