Am I pushing my bank too hard?

[dougweibel]

I have four Fullriver DC400-6 deep cycle AGM batteries for my house bank. I recently upgraded my solar so we have been using the house bank for more energy intensive uses such as using the convection oven instead of the gas oven, etc. I never worried about using the microwave before as even though it was a very high current draw on the house bank it only lasted minutes. Now we may be drawing 140 amps for an hour. We never discharge more than 250 Amp-hours so have good safety margin as far as energy used, and with our solar we reliably get back to a 100% state of charge daily unless we have extended heavy overcast weather. Even with 50% cloud cover all day we will be at 100% at 5 PM.

I'm curious to hear what any AGM experts think about the practice of pulling larger currents for substantial times. From Fullriver's data sheet it would appear this should be OK. They have a table for constant current discharge rate and I'd be only at a 0.20CA rate and only going 20% of the discharge time (granted the discharge time is 100 SoC, but I'm only 40% for a 50% SoC).

Is this practice shortening the bank's life? If so is it a substantial change? If I'd be getting 1000 cycles and will only get 800, I'm fine with that.

[sailorboy1]

well hard cycling always reduces life, but I would guess that it isn't as important as the impact of getting fully charged

[Paul L]

A convection oven for an hour is not the most practical item for a boat. Are you really able to get these batteries back to a true 100% state of charge? If not, you will slowly kill them.

[dougweibel]

Originally Posted by Paul L

Are you really able to get these batteries back to a true 100% state of charge?

Well, by the normal methods of measuring state of charge I'd say yes. My Victron battery monitor shows we reach 100% charge AND my Victron solar controller goes through bulk and absorption phases and reaches float.

By what other criteria could I judge a true 100% SoC?

[dougweibel]

I would agree that a convection oven is not the most practical, though I see more people with large wind and solar capacity going to all electric galleys. However for us it is more a matter of baking bread twice a week and wanting to run some laundry every week or so and having free energy with our added solar. Why burn the diesel and propane unnecessarily?

[Paul L]

Originally Posted by dougweibel

Well, by the normal methods of measuring state of charge I'd say yes. My Victron battery monitor shows we reach 100% charge AND my Victron solar controller goes through bulk and absorption phases and reaches float.

By what other criteria could I judge a true 100% SoC?

The current at absorption voltage is between 1% and .05% of the bank capacity. Most chargers and monitors claim 100% sognificantly before this state.

[CharlieJ]

I reviewed the FR spec sheet and it looks to me like you are operating well within the published parameters. With a normal DOD of about 30%, the service life plot shows that you should achieve about 1700 cycles.

Note that on the constant current plot discharging at the C20 rate (20.8A) or at the C5 rate (68A), the voltage profile is flat at the 1 hour mark.

Three very important ways to improve the service life of AGM batteries:
1. Use them; don't abuse them. LA batteries need to be exercised to be healthy.
2. Use temperature compensation for all of your charging sources.
3. Fully charge the batteries after use or as frequently as is possible.

BTW, the Full River spec sheet is one of the best spec sheets that I have seen.

[dougweibel]

That doesn't seem like useful information. How can one get current at 0.5% of bank capacity at absorption voltage if all chargers have already switched to float voltage before that low current is reached.

That criteria doesn't even seem relevant to my situation as it would not matter if I pulled another 100Ah out of the bank a given day or not. That energy gets put back in the bank in the bulk phase and only delays the time in the other phases by a couple hours. If you want some extended low current charging time it won't happen either way as the refrigerator runs at night but the sun does not shine.

[OneKoolCat]

I also use the Victron to get me all charged up. I think that if your Victron charge controller is programmed for your battery then I think you are ok on the charging end. They have some good products that do a good job charging.

I am assuming you have a 12v system. That would mean that you have 2 battery blocks pulling 70 amps each. (each of those made of 2 batteries each pulling 70 amps at 6v) From their sheet 68 amps is 0.20CA. 5 hours until dead. As long as you are not cheating too much I think you are ok. Personally, I would rather use a battery than keep it as a decoration.

I also feel that cooking with electricity works well on a boat, but I also have an electric outboard on my dinghy. If you can make some low carb bread I will swing by later.

[dougweibel]

Originally Posted by CharlieJ

BTW, the Full River spec sheet is one of the best spec sheets that I have seen.

Thanks Charlie,

It seems battery spec sheets never have exactly in info you'd like to know but I agree the FullRiver spec sheet has a lot of info.

[rslifkin]

Originally Posted by dougweibel

That doesn't seem like useful information. How can one get current at 0.5% of bank capacity at absorption voltage if all chargers have already switched to float voltage before that low current is reached.

Ideally, the point when chargers drop to float is controllable. I know the Victron solar controllers (with new-ish firmware) can switch based on end amps. And if you have their battery monitor networked to the controllers (either via VE.Smart or though a GX device with DVCC), it can use the amps sensed by the battery monitor for the change, which accounts for multiple controllers as well as loads.

[dougweibel]

Originally Posted by rslifkin

Ideally, the point when chargers drop to float is controllable. I know the Victron solar controllers (with new-ish firmware) can switch based on end amps. And if you have their battery monitor networked to the controllers (either via VE.Smart or though a GX device with DVCC), it can use the amps sensed by the battery monitor for the change, which accounts for multiple controllers as well as loads.

Good point. I've got two Victron solar controller, one older on some smaller panels and one new on larger panels. I checked on the newer and you have to open the 'expert settings'. The default tail current is 2.0 Amps which would be only 0.25% in my application, so pretty low already. You can change the max absorption time up from a default of 6 hours but that seems unnecessary as I do transition from absorption to float.

[sailorboy1]

[QUOTE=dougweibel;3361512 You can change the max absorption time up from a default of 6 hours but that seems unnecessary as I do transition from absorption to float.[/QUOTE]

you don't fully get it and appear to want to disagree with people providing the answer to your question

Doesn't matter what your charger/controller does, all that matters is how much current the batteries accept at absorption voltage. If the current at absorption does not drop to whatever you manufacturer says equals fully charged then you aren't 100% charged. Doesn't matter if a battery monitor or smart gauge says you are of that the charger/controller went into float. People mistakenly believe they are at 100% when they are 99% partial state of charge.

There are lots of threads about this if you really what to understand. But I have lots of cruisers who don't and still get about the same life because battery life on an off grid cruising boat never matches the factory use life.

[dougweibel]

Perhaps I don't get it but I fail to see how.

I fully understand using the criteria of absorption current falling to a certain level as a criteria for determining 100% SoC. My charge controller is currently programmed to switch from absorption to float at a current that is ~0.25% of the bank Ah capacity. The manufacturer, in a spec sheet cited in this thread as being a pretty good spec sheet, gives no guidance on what current level should be used to conclude absorption. Paul L suggests a range of 1.0% to 0.05%, a range that spans a factor of 20. I am well within that range. Are you suggesting I need to be lower in that range? Why?

[sailorboy1]

Originally Posted by dougweibel

Are you suggesting I need to be lower in that range? Why?

I am 100% positive I posted what to use for your batteries to determine 100% charge.

I am now unsubscribing to this threads that has been fully answered.