Battery @ 11.75v under sustained 8 amp load

[waterman46]

Originally Posted by Mike OReilly

In the evening I can start with a fully charged bank (according to my Victron meter), but after ~ 8 to 10 hrs I'm measuring 11.75 volts while under 8 amp load. Lighten the load to 1 amp and the voltage rises to 11.9v fairly quickly, and might get up to 12v after a few minutes.

You say the bank is fully charged according to the Victron but you didn't mention what that voltage is and what are the current conditions, when you consider it fully charged. You mentioned a significant difference between the Victron and your solar controller. If they are really connected to the same place (hopefully at the batteries) and if you didn't notice any actual performance problems then it looks like the Victron meter might be just reading low.

You mentioned drawing 8 amps for about 10 hours, which is 80 AH and your battery bank is about 4 times that if fully charged. I'd guess the true no-load, at rest voltage at that point should be about 12.8V but you can look up such stuff in the literature.

[mitiempo]

Mike

If programmed correctly your Victron monitor will consider your bank fully charged when the batteries are accepting 2% of bank size - 7.2 amps. This is not fully charged but it is what monitors consider fully charged.

Your batteries are really fully charged when they are accepting .5% of bank size - in your case that is 1.8 amps.

The above obviously depends on charging current availability from solar or wind gen.

When your monitor thinks the batteries are full check the current in with all loads off. I think your monitor is misleading you into thinking the bank is fully charged when it's not close.

You state that the voltage rises slowly then rises quickly - that doesn't seem right. The batteries will accept less and less current as they approach full - this takes a long time.

[Maine Sail]

Originally Posted by mitiempo

Mike

You state that the voltage rises slowly then rises quickly - that doesn't seem right. The batteries will accept less and less current as they approach full - this takes a long time.

What Mike is likely seeing is the wind / solar controller in bulk as the "slow rise" then the On/Off regulation once the bank has achieved the OFF point of approx 14.2V. The problem with On/Off regulation is that while fine for wind, it is horrible for a live-board cruiser an far less than ideal for solar.

An On/Off controller will never get his batteries anywhere close to full in a single solar day. Heck getting to 100% SOC in a single solar day is extremely difficult even with PWM or MPPT & faster charging AGM's.

By not getting full every day Mike's battery capacity will gradually "walk down" from continual PSOC (partial state of charge cycling).. On/Off regulation is necessary for wind, otherwise the unit would murder itself, but On/Off is really quite abysmal for solar which is great for "finish charging"...

Mike really needs a fully programmable PWM or MPPT solar controller. Wind is a very good bulk charging source & solar is a good bulk and absorption source. Trying to use a one size fits all controller for both wind and solar really defeats the ability of solar to bring your batteries to the highest possible state each day.

Unfortunately Mike's controller will not let his solar array provide a proper absorption cycle because it does this: (voltages are approximate)

On at 13.2V > Off at 14.2V > Battery Voltage Decay's Back to 13.2V > On at 13.2V > off at 14.2V > Repeat > Repeat > Repeat

With On/Off regulation voltage never held steady at an absorption level. A proper absorption cycle is quite critical for optimal battery health especially in a daily deep cycling application.

A PWM or MPPT controller will bring the batteries to absorption level voltage then hold the absorption voltage steady, at the desired set point voltage, and will yield significantly faster & healthier charging during the day. For live-aboard cruisers who cycle daily a proper absorption charge and the correct voltage is absolutely critical to minimize cycling capacity "walk down" and to minimize the effects of PSOC cycling and the resulting sulfation..

In short voltage is not held steady with On/Off regulation and instead of absorbing it can actually spend more time off than on once it has brought the batteries to absorption voltage.

A pulse width modulating regulation (PWM or MPPT controller) never stops charging and holds voltage at the desired set voltage for the programmed duration until it drops to float. Even AGM batteries, when basically brand new, still require as many as four plus hours of absorption charging, after bulk is over, at a constant voltage that is held steady. By ping-ponging off and on the battery is essentially going straight from bulk to a "floatish" state which causes charging, after bulks ends, to be measured in terms of days not hours...

[Maine Sail]

Damn editing time-out feature... It's really too bad the mod team does not trust us to edit our own postings.....

This is a quick drawing of the two differing types of solar regulation:

The larger the array with On/Off the earlier the ping-pong On/Off game starts in the SOC curve. With a very small array & On/Off regulation you may get into the mid 90's, as a percent of SOC, before this begins but with a 400W array and wind power, on a 360Ah bank, this is happening far to early in the SOC range and drastically cutting into charge speed.

Mike could be attaining 14.2V as early as 70% SOC, at an approx .1C charge rate, especially if sulfation has already begin to set in.

Bulk: During bulk (often referred to as constant-current) the battery voltage is slowly rising to the absorption level (also called constant-voltage). In bulk the solar and wind are supplying all the current they can until the voltage rises to the transition point of bulk to absorption.. The rise graph with solar or wind (burgundy line) will not be as steady as I drew it in the real world, but bulk just means the wind & solar are producing all the current they can with what they are being given by mother nature. Both On/Off controllers and PWM/MPPT controllers do bulk.

Absorption: During the absorption stage voltage is held steady, the battery begins gassing (healthy) and lead sulfate formed on the discharge is reconverted. Once voltage is held steady current begins to decline, it has to.. On/Off controllers do not do an absorption stage they go straight from BULK to On/Offing.

Float: Float is a further reduced constant-voltage stage where the battery can charge nearly indefinitely with minimal harm. On/Off controllers do not do float they just continue On/Offing. To continue this type of floatish behavior, with an On/Off controller the OFF voltage has to be set lower so as not to eventually cook the batteries, especially when they are not being used but still being charged.

[Mike OReilly]

So, as a follow up, or continued saga, I was on shore power for two days and charged the batteries via my 3 stage charger. First night on anchor saw a draw down of 55 amp-hrs overnight and a voltage of 12.3-12.4. So not great but far better than previous.

This seems consistent with MS's diagnosis of poor charging. Since I have lots of charging power this all points to the crappy controller. So it's off to the boaty store for a new mppt as soon as I can get there. In the mean time I'm going to try and get the batteries on the alternator as much as possible (we don't motor that much), and maybe even use the little emergency gas generator every once in a while.

Thanks to everyone, esspecially Main Sail, for all the help. Really appreciate it.

Btw, given my numbers I also think my bank is alot smaller than 360 amp-hrs. Perhaps as low as 200. Could be a damaged/dysfunctional battery in the lot. I'll do a resting voltage check as soon as I can.


Why go fast, when you can go slow

[a64pilot]

Use the little gas generator it's cheaper in the long run than the propulsion motor, and I know nothing about your controller, but I'd set it for absorption voltage and not let it float.
Maybe set absorption and float to the same voltage is one way, but I seriously doubt you will be overcharging your batteries with Solar, especially being way up North.
I've come to the belief that it is essentially not possible to fully recharge normal lead acid batteries from Solar, no matter how big the array so you may be better off using your generator early in the morning when acceptance rate is high and getting some amps back on, then going to Solar when it can supply all the batteries will accept.
Its all theory as I'm not cruising yet, but it's my plan and I expect to have a Kilowatt of Solar, but think I'm doing a generator run twice weekly.


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[Maine Sail]

Originally Posted by a64pilot

I know nothing about your controller, but I'd set it for absorption voltage and not let it float.
Maybe set absorption and float to the same voltage is one way, but I seriously doubt you will be overcharging your batteries with Solar, especially being way up North.

He has an On/Off regulator it won't do a typical absorption or float it just bounces between an On voltage and an Off voltage once the target voltage has been attained.

[a64pilot]

OK didn't know that.
If you had a single 250W panel, what is a decent MPPT, price is a concern? Sort of a hijack, but maybe not as it seems he needs one too.


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[DeepFrz]

Mike, how many cycles to 50% DoD are your batteries rated for. If they are not "true" deep cycle batteries they may already be on their last legs. You have been taking them down well below 50% DoD so I would suggest you do a capacity check on them.
What Is A "Deep Cycle" Battery? Photo Gallery by Compass Marine How To at pbase.com

[fallingeggs]

Originally Posted by a64pilot

If you had a single 250W panel, what is a decent MPPT, price is a concern? Sort of a hijack, but maybe not as it seems he needs one too.

As MS points out, the Morningstar TriStar MPPT line (30, 45 and 60 amps) are excellent. They have presets for the major battery types, but also allow for custom settings.

The 30 amp would be large enough.

Morningstar does have a 15 amp MPPT that is at a lower price point called the Sun Saver. I don't know much about it, but it probably doesn't have the custom settings of the TriStar. Probably works well enough though as it certainly has the three stage charging profile. 240 watts would be pushing a 15 model though, but take a look at the manual.


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[MarkJ]

Whilst I think the Million Dollar Controller is going to be better, I think you are just buying a panacea to the real problem: 8 amp continous drain.

Sucking 8 amps during the day means you need a thousand solar panels and 3 lightning strikes to charge your batteries.

The priority is to get that 8 amps suck down, imho.


Mark

[a64pilot]

Oh, I wish I could get my consumption down to 8 amps


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[a64pilot]

Fallingeggs,
Thank you.


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[Mike OReilly]

Originally Posted by MarkJ

Whilst I think the Million Dollar Controller is going to be better, I think you are just buying a panacea to the real problem: 8 amp continous drain.



Sucking 8 amps during the day means you need a thousand solar panels and 3 lightning strikes to charge your batteries.



The priority is to get that 8 amps suck down, imho.

Agreed. If I could get my draw down to something reasonable, say even 5 amp, periodic draw, I'd be in amp-hr nirvana. Looking to replace the old Aldur Barber as well.

Damn... the price of cold beer keeps going up.


Why go fast, when you can go slow

[a64pilot]

See I don't think the old Adler barbor is that bad efficiency wise, I think you need insulation to get the run time down and that is they way to lower power useage.
I don't think a new machine would be much more efficient but very expensive and insulation may not be all that expensive, but increase efficiency quite a bit.


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