I can't seem to find this question addressed here. I have several choices to keep the battery charged but which one is better, if in fact one is preferable, than the others and why? The charger that is built into my RJC genset.
The charger that is built into the ATS. A standalone commercial battery charger (float or otherwise) My inclination is to let the genset charger do the charging just because the wiring is already in place and requires no extra effort on my part. A side note: I need to replace the current battery with a new one.
I'm eyeing a 900 CCA battery at Sam's that is priced at $110 and would fit in the allotted space easily. Is there any reason to think differently? When you say the RJC charger are you talking about charging the battery only when you run the unit. If the transfer switch it an older Onan type with the constant milliamp output, they work but tend to cook batteries over the long hall. Battery charger technology has come a long way, I would opt for a newer charger. There are so many to chose from. The ones that I see mostly are the type mounted on the wall in permanent installation.
Sens is a popular one. What is your situation, Trailer mounted, permanent install or something else? I might recommend looking at chargers designed for a marine application simple do to there weather / water proof design. I would get a battery of the BCI group 27 or 31 if it will fit. Bigger is mostly better. I have not heard of any one battery MFG that fail more than any other. I am buying two NAPA marine batteries for a customers boat tomorrow to match the other two he already has.
Onan 6500 Battery
They sat on my basement floor all winter and still had good voltage. Got my RJC sitting on EBay, No battery going with it. I'm glad I asked. I really value the opinions I get here and I'm proud to be associated with this group. I just ordered the following off Amazon. Schumacher SEM-1562A 1.5 Amp Speed Charge Maintainer. Suggested retail $50, Amazon price is $19.00.
This one is so cheap that I can throw it away if I don't like it and buy another one and not feel bad for trying it. This genset is permanently positioned in the back yard. I have the natural gas plumbed to it and that part works fine. Next on the list is to run the wiring to the ATS (about a hundred feet) I may get that done tomorrow.
Onan Generator Battery Charger
I am only concerned about big storms (hurricanes) that seem to hit Houston every 25 years on average. The last one (Ike) was in 2008 and I had no power for 16 days. That's when I decided to research standby generators and get one installed before the next 'big one' comes calling. I do notice that the folks in the central and northern US seem to buy a lot more residential generators than the people further south. You might want to consider modifying the charging circuit of the genset to prevent possible overcharging problems. You could put a blocking diode in the circuit to prevent charging altogether, or try to adjust the charge circuit voltage to the minimum voltage based on temperatures you are likely to see in your area. Here's a good write up I found: Temperature Effects on Batteries Battery capacity (how many amp-hours it can hold) is reduced as temperature goes down, and increased as temperature goes up.
This is why your car battery dies on a cold winter morning, even though it worked fine the previous afternoon. If your batteries spend part of the year shivering in the cold, the reduced capacity has to be taken into account when sizing the system batteries. The standard rating for batteries is at room temperature - 25 degrees C (about 77 F). At approximately -22 degrees F (-27 C), battery AH capacity drops to 50%. At freezing, capacity is reduced by 20%. Capacity is increased at higher temperatures - at 122 degrees F, battery capacity would be about 12% higher. Battery charging voltage also changes with temperature.
It will vary from about 2.74 volts per cell (16.4 volts) at -40 C to 2.3 volts per cell (13.8 volts) at 50 C. This is why you should have temperature compensation on your charger or charge control if your batteries are outside and/or subject to wide temperature variations. Some charge controls have temperature compensation built in (such as Morningstar) - this works fine if the controller is subject to the same temperatures as the batteries. However, if your batteries are outside, and the controller is inside, it does not work that well. Adding another complication is that large battery banks make up a large thermal mass.
Thermal mass means that because they have so much mass, they will change internal temperature much slower than the surrounding air temperature. A large insulated battery bank may vary as little as 10 degrees over 24 hours internally, even though the air temperature varies from 20 to 70 degrees. For this reason, external (add-on) temperature sensors should be attached to one of the POSITIVE plate terminals, and bundled up a little with some type of insulation on the terminal.
Battery For Onan 4000 Generator
The sensor will then read very close to the actual internal battery temperature. Even though battery capacity at high temperatures is higher, battery life is shortened. Battery capacity is reduced by 50% at -22 degrees F - but battery LIFE increases by about 60%.
Battery life is reduced at higher temperatures - for every 15 degrees F over 77, battery life is cut in half. This holds true for ANY type of Lead-Acid battery, whether sealed, gelled, AGM, industrial or whatever. This is actually not as bad as it seems, as the battery will tend to average out the good and bad times. One last note on temperatures - in some places that have extremely cold or hot conditions, batteries may be sold locally that are NOT standard electrolyte (acid) strengths. The electrolyte may be stronger (for cold) or weaker (for very hot) climates. In such cases, the specific gravity and the voltages may vary from what we show.
For this reason, external (add-on) temperature sensors should be attached to one of the POSITIVE plate terminals, and bundled up a little with some type of insulation on the terminal. I agree that temp sensor needs to be at bat. And on a post is better for themal conductivity to sense intenal bat temp. But why the Positive termainal?? Would guess thermal path length to internal plates is same on both terminals. Less chance of shorting out the chargers internal circuits if sensor shorts to terminal??