House battery problems
Sorry for the long post but recently, I have been frustrated with the performance of the house battery system in our 2001 SMB. We have a single AGM 4DF battery that was last replaced in September 2007, about 18 months ago. We have three 60-watt solar panels that should provide a theoretical 20 amps of charging.
When the van was new, we were able to camp for 2-3 days without shore power and without being concerned about the capacity of the house battery, even without solar. We could run the lights for a while and then watch a couple of hours of TV without drawing the house battery down too much. However, now, even with trying to minimize use of the lights and with the refrigerator turned higher than we used to do, the house battery will drop down to 12.2 v overnight.
I’ve thought about a few things to check and some possible solutions. My first idea was to add a second AGM battery but we have the Transfer Flow twin gas tank option and the area behind the rear axle is taken up by the second gas tank. Space along the frame rails is taken up by the single AGM battery, an air compressor, and, on the other side, the propane tank. Inside, we have a hot water heater, inverter, and Suburban heater. So, I don’t see any place to add a second house battery.
My next thought was that the 4.1 CF refrigerator is getting old and running more often that when it was new. I’ve read that the compressor on these units isn’t that efficient nor serviceable. So, I started taking some voltage and amperage measurements. For these measurements, I used the voltage and amperage readings on the solar panel meter (which I believe are measuring only the output of the solar panels) and a Link 10 Emeter which I believe reads the net amperage on the house battery. (Both meters show the same voltage when at rest, i.e., the solar panels are not charging; when the solar panels are not charging, the Emeter shows the amperage draw of wherever is on.)
After taking readings under different circumstances over the past several days, I have some questions:
At 8:00 pm at night (no solar charging), the house battery voltage read 12.8 v (more on that further on). Everything in the van was off including the detectors. The Emeter amp meter read 0.00. I turned the refrigerator on (with the thermostat at 3 o’clock) and the house battery voltage dropped immediately to 12.6 v and the draw measured –2.6 amps. A half hour later, the battery was reading 12.4 v and the draw was up to –3.4 amps. At 10:00 pm, the refrigerator had turned off (the temperature stabilized at 47.5 degrees) and the house battery voltage moved back UP to 12.6 v. I turned the thermostat to the 6 o’clock position, the refrigerator turned back on, and the voltage DROPPED back down to 12.4 v and the amperage increased to –3.9 amps. By 7:00 am the next morning, the battery was down to 12.3 v (solar was putting out only 0.02 amps and thus hadn’t started recharging the battery). Absolutely nothing else was on during the 11 hours, no lights, no detectors, etc.
Question – Anyone have an idea why the amperage draw of the refrigerator increased from 2.6 amps to 3.9 amps either with a lower temperature setting or the longer the refrigerator ran? I guess that it is possible that more amperage might be needed with lower temperature settings but it seems to me that, instead, the compressor would just need to run longer to result in/maintain lower temperatures.
SOLAR PANELS OUTPUT
On another day, I turned on the refrigerator, the inverter, and the microwave and ran them for a few minutes to “force” the solar panels to charge the house battery. The time was close to noon and the sun was about 30 degrees from vertical. The house battery measured 12.8 v. However, the solar panels only put out only 7.6 amps. At other times, the most I have seen is 9.0 amps. (When camping, the low angle of the sun in the mornings results in low amperage output from the solar panels and we rarely if ever use electrical devices in the mid-day, so I’ve never previously thought about a low amperage output from the solar panels.)
Question - Even in discounting the sun angle, inefficiencies, wiring, etc., it would seem that the output of 240 watts of panels should be more than 9.0 amps. Has anyone else checked the output of the solar panels? Does this seem correct?
SOLAR PANEL CHARGING
While watching the output of the solar panels, I noticed a difference in the amperage readings of the solar panel amp meter and the Emeter amp meter. Nothing was turned on and both meters should (I think) have shown the same reading since the output of the solar panels should be the same as the net reading shown by the Emeter. But the Emeter consistently showed a net amperage 0.5 amps less than the solar panel meter. For example, when the solar panel meter showed 9 amps output from the panels, the Emeter showed a “net” amp reading of 8.5 amps and, later in the day with the sun lower, the solar panel meter showed 4.7 amps while the Emeter showed 4.4 amps. That suggested to me that something was on and pulling 0.5 amps. But nothing was on, not even the detectors. Any when the panels were not charging, the Emeter showed zero amps.
Question – Any reason for this discrepancy? Is this normal?
The house battery “rest” voltage seems to vary. The first day I recorded it (with nothing on), the house battery read 13.2 v during the day. I then checked it at 8:00 pm (dark and no solar charging) and it read 12.8 v. It read the same at 9:00 pm and 10:00 pm. But by 6:45 am the next morning, the voltage was down to 12.7 v. It doesn’t get that cold here…the lows have been around 45 degrees.
This lead me to take a harder look at the solar panel charging…
SOLAR PANEL CONTINUOUS CHARGING
During the day, with nothing on, the solar panels should be “at rest” and not charging the house battery. However, I noticed that the battery will be at 13.0 v when the panels are not charging. But the panels then charge for about 2 seconds (at 9 amps on the solar panel meter and 8.5 amps on the Emeter)…the battery voltage steps up from 13.0 v to 13.6 v to 13.8 v to 14.0 v to 14.2 v (the Charger Set Point is set at 14.4 volts) before turning off. Over the next 10 seconds or so, the house battery voltage steps back down to 13.0 v. After a couple of seconds, the solar panels start charging again, running the battery up to 14.2 volts, etc., etc., etc. Again, nothing is on…just to be sure, I turned off the circuit breakers and pulled the fuses. This charge/rest/charge/rest thing goes on all day long. When I started the van, the alternator charged the house battery to “14.4 v” but that reading could have been the alternator output. As soon as I turn off the engine, the house battery voltage starts dropping again, coming back down to 13.0 volts and then the charge/rest/charge/rest operations starts again.
CONCLUSION AND ULTIMATE QUESTION
This is a lot of information but I think it is related (except for the low output of the solar panels). When nothing is on, the Emeter shows a reading of 0.5 amp less than the solar panels are putting out. Most importantly, the solar panels continually charge during the day. At night, the panels, which were reading 13.0-13.2 volts at rest, drop to 12.8 volts. The refrigerator then pulls the battery down to 12.2 volts overnight, with the amperage draw increasing during the night. So, without lights or any other load, the refrigerator drains the battery to 50% capacity. The battery is only 18 months old with only about 40 days of camping since it was new. So, it seems something is causing the house battery to continually drain all of the time.
Thanks, it is driving me crazy….
Re: House battery problems
I'm sorry, this is only going to address a tiny portion of your problem. But 9A from 180W of solar seems reasonable - 20A is way off. You should be able to quickly search your panels' model number and find the specs.
Are the panels themselves drawing power from the battery at night? There should be a diode inline to prevent this.
Re: House battery problems
I don't have solar so I don't have a lot experience in that area. What does your E-meter say it has used up in amp-hours during your overnight run. Even if you ran fridge ran constantly it seems that you would have only 25% of your available battery. I have the smaller fridge, and the current draw appears to be the opposite, usually I see higher current when it turns on and then it drops as gets to the end of the cycle. It does sound like your battery is shot, but your $500 question is what is killing it. Where are the DC shunts for the two meters installed?
Re: House battery problems
I have a similar setup as you do except I don't have a Refrig drawing power but have lots of 12v devices; lights, clocks, 12v power supply for car computer, etc.. even my voltage readings are close to yours.
I have two Kyocera GT130 watt solar panel going to a 20amp rated solar charge controller.
During winter, and spring seasons, the most I've seen the solar charge is about 9amps also via the Link-10. During summer though, I've seen it as high as 14amps (each panel is rated at 130watts, 7+ amps potential).
I did have this strange amp draw that you were experienced and found out that if your on shore power charging your house battery, any 12volt draw (like a like, or refrig) will steal the charge off your house battery. So when it's doing it's 3 stage charging and it's done, any 12volt draw will steal the amp hour cabability from the house battery for the next day. In your case, the 12v fridge and some possible unknown device..
This explained my question I had a few months ago about why on Mondays, when I got to work, it doesn't seem to have a enough charge on the house battery but on Tuesday's - Fridays, it's all good. During the weekend, my 12volt devices discharged the house battery a bit..but it added up.
Two things I did to fix the problem:
A year ago, Thinking about how I solved the solar issue when I'm on shore power, I had added a relay to make sure the solar wasn't pumping volts/amps to the house battery when I was on shore power, so..
To fix this recent problem, I bought a 12v 30amp power supply and added another relay. When I plugged the house battery to shore power, it switches the 12volt draw from the house battery and draws from the power supply, thus stops the backend stealing of amp-hours.. from the house battery.
I also re-wired the main 12v panel where it goes from the house battery to the panel and added a main cut-off switch (Big Red Key), that cuts off all 12volt to the panel that connects to all 12volt device from the house battery (minus the 12v line from the inverter that charges the house battery) (now all that I've discussed above, the Inverter is "OFF" and not inverting, about the only thing it's doing is help charge the house battery when I dock it to shore power)
Since I have the Link-10 amp wired correctly to see how much 12v amps are being drawn from the house battery, turning the 12V cut-off switch would drop the amps to 0. This made me confident that nothing was drawing 12v from the house battery. I also use the cutoff to turn off all devices to get an awesome charge on the Solar Panels when camping also.. saves on trips filling the Honda2000 during the day also.
So with the 12v Main cut-off swtich on, I start a few lights on, one by one, and I confirmed the amps drawn by each device.. kinda nice to see how much an orginal normal bulb sportsmobile light draws versus an LED light..
Question: Have you watched your amp-hours in on the Emeter after a good charge and compared it to amp-hours in the morning without the fridge on?
Question: Does your fridge offer a 110V option versus 12volts so you can connect it to shore power?
My propane fridge can also do 12volts and 110.. When I'm at home/work and not camping, I actually have the fridge set to use 110 shore power all night long and run it "without" propane during the day. With a few cold packs, it actually makes it through the day and starts getting it colder to 37 degrees when I dock back at home. I do set it propane when we go camping..
I also have a dedicated 110outlets(shore power) for my portable air conditioner and heater seperate from the 110v Inverter outlets for summer and winter seasons.
It's been a do-it-yourself fix for me but it's awesome to see the solar panels charge up the house battery to full by the end of day after using almost half of the battery during the mid day..(microwave, computers, TV/DVR, fans, etc)
I was thinking it was the battery also, but it wasn't..
Re: House battery problems
I’ve had a couple of off-forum e-mails regarding my problems. Charlie (Charlie56/R Hogan) is an architect (he designed a pair of my public building projects) and passed my problems on to his electrical engineering subcontractor. This engineer provided some insight to the difference in readings between my solar panel amp meter and my Emeter:
You mentioned the difference in the two meters and what they show in amps. That's probably just related to the losses in whatever is between the two measuring points (i.e. inverter or solar controller). I assume the solar meter is measuring solar output at the input terminals of the controller (before conversion or adjustment) and the other one is the bus between the batteries and the solar controller output. So there is some equipment between them and that takes some power loss for conversion, which you'll see as a net difference in the amps at the two locations.
He also commented on the increase in refrigerator amp draws:
For the refrigerator, part of what's going is that it's probably acting like a constant power system when a load like a compressor is on it. As the voltage goes down, the required current goes up to keep roughly the same amount of power (volts times amps = watts = power).
Our friend John Kalmbach had problems posting to the group and e-mailed me directly. Summarizing his comments…
Regarding the readings of voltage and amperage draw, John said:
These readings are not uncommon for the refrigerator. It is uncommon for the battery voltage to drop so quickly, but the amperage readings look normal. Your Norcold should have a label inside stating it's amp draw, I believe it is 4.1 amps at 12vdc. This would mean it takes about 49 watts of power to operate it (amps x volts = watts). This is roughly what you were seeing with your numbers at the 6:00 o’clock [thermostat] setting. There are many variables that affect the current draw; temperature and pressure fluctuations within the refrigerant system can really alter the load on the compressor.
John was pretty close….at 12vdc, our refrigerator is rated to pull 3.1 amps which would be 37.2 watts. Our refrigerator is therefore pulling 32.8 amps, 42.2 amps, and 48.4 amps as the battery is discharged. As Charlie’s electrical engineer mentions, as the battery voltage goes down, the amps would increase. So, it sounds like the refrigerator is okay although we are giving serious thought to replacing it with a Cruise 130 ASU which is the unit that Charlie has in his SMB.
SOLAR PANELS OUTPUT
As Mike mentioned, my solar panel output is reasonable. I knew I had 240 watts of panels and divided by 12v to arrive at an expected 20 amps. Regarding getting 9 amps out of them, John said:
This does seem correct. The manufacturer rates the solar panel at a maximum charge voltage of 17.4vdc. 180 watts / divided by 17.4vdc = 10.3 amps. This is of course with new panels (they tend to degrade about .5% per year), directed at the sun. Actually, your panels would provide 10.3 amps at best, so getting 9 amps is not bad at all.
DIFFERENCES IN SOLAR PANEL METER AND EMETER READINGS
I was concerned about the difference in readings between the meter on our solar panel and the Emeter. Charlie’s engineer, as mentioned about, felt that those differences were not unusual. John agreed:
I think this is normal. There will be some discrepancy because of line loss when the panels are charging. Where the connections are made for the Emeter and solar controller will also effect the readings.
Our house battery “rest” voltage seemed to vary. John told me:
12.8vdc is a fully charged battery. It can take up to an hour for the battery voltage to "rest" after the charge source is removed if there is no load on the battery.
In addition, Charlie’s engineer told me:
So when you measured the bus voltage at night, you’re getting an indication of the battery voltage. I'm not sure where the 13 volts comes from, since there's nothing you have that should be boosting the standard battery voltage to 13 volts at night. Or that 13 volts is the open circuit voltage after charging, which will quickly get sucked down as soon as you draw even a little current. [That is obviously what is happening.] When you turned the engine on, you’re reading essentially the voltage regulated output of your alternator, which is close to 14.4 volts on the bus. When you turn the van off, the 14.4 volts should drop fairly quickly back down to near the battery voltage and that will vary depending on load. If it's dropping even further at night with no load, then you most likely have an electrical leak (something drawing current), or the open circuit voltage of your battery is actually closer to 12.2 volts and with no load it's just taking all night to slowly get down to that open circuit voltage after having been temporarily charged by a higher source like the solar panels or alternator.
Finally, I was worried about the house battery continually being charged by the solar panels. John’s opinion is:
The solar controller has a high and low charge set point. It allows current to pass to the battery whenever the voltage falls to 13.2vdc, and it stops allowing current to pass to the battery once it increases to 14.4vdc. This is actually a good thing as it conditions the battery and disulfides the cell plates. But too much cycling may not be a good thing (on this point I'm speculating).
John went on to suggest some things to check regarding the continuous battery charging:
While it is possible your battery is bad, I really doubt it. I think it may be more of a grounding issue.
Check the battery cable terminal ends, especially where the ground cable attaches to the chassis. Also check the positive cable and other visible wiring to see if it has chaffed through the years and is grounding somewhere.
Another area to check is under the hood at the Battery Isolator. Confirm there is no corrosion or rust on the Isolator which is located under the coolant recovery canister. Also, trace the 4 gauge wire coming off the Isolator, it should route to a small (1 1/4" x 3/4") 50 amp circuit breaker. This breaker was eliminated in later year model SMB's, and you can eliminate yours too. I have seen these breakers corrode and rust internally, thereby allowing current to flow to the chassis and discharge the house battery. This circuit breaker is typically located behind, above, and slightly inboard of the diver side headlight.
You may also need to equalize your battery to get it to function like in the past.
NRL made some suggestions regarding potential problems with shore power but, with solar, we never hook up to shore power. Tomorrow, I will check out the items John mentions…I’ll let everyone know what I find out.
Re: House battery problems
Jack FWIW I was told that a link-10 monitor will pull a bit of amperage itself in operation. I can't confirm this and would not think it would be in the area of .5 amps anyway, but you might check with Xantrex. As far as your solar output, that seems up to par. I don't know what controller you're using but when I switched from the Specialty Concepts Mark PV controller to the Blue Sky unit, the amperage dropped from about 8+A to around 5 or 6 on similar days. I thought I had a panel failing but was told the Blue Sky will only put out what the batteries need. I'm not too sure about this and plan to cover each panel and do some amp checks. Good luck on your problem.
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