Batteries and SOC

[Christianonthecut]

Hi all,

 

I have 2 x110Ahr Numax CXV's which are nearly 10 months old. After recently fitting solar and a shunt I have been keeping a close eye on usage and energy harvest which has led to trying to work out what the capacity of my 10 month old CXV's currently stands at.

 

I can't SG the cells as they are sealed but by taking voltages and then comparing against AHr's used. I think that the 220Ah pair are currently holding about 70Ahr full capacity!!

 

They have been below 50% SOC at times, but surely they should still be healthier than this at 10 months?

 

 

 

 

[nicknorman]

My recent experience (limited, not being a live aboard) is that even with a good charging regime batteries lose capacity fairly quickly, presumably due to sulphation. I changed our first set of batteries after just over a year because thy seemed to be down to 50% of original capacity despite always fully charging them at 14.4v with the engine alternator, and leaving them on float charge when in the marina.

 

The new set of batteries started to go the same way. The cure was to apply an "equalise charge" once they were fully charged. I applied 15-15.5v (depending on temperature) for a coupe of hours whilst monitoring the current and temperature (current should be only 10A or so). Full capacity was restored.

 

In your case you will have to be careful not to lose battery water from excessive gassing because your's are sealed. Next time I would recommend unsealed batteries so that you can top them up.

 

Now that you have solar, the chances are that once you have done an equalise they will remain in better condition, at least over the summer.

[DeanS]

Could someone explain EXACTLY how you do an equalise charge if :

 

1. I have a gennie.

2. I have an engine

3. I have 920W of solar

4. I have a bank of 3x110AH unsealed batts connected to another 3x110AH of sealed batts (I forgot to check when ordering).

 

At the moment I'm seeing batts at a decent voltage all day due to the impact of solar, and a fairly quick descent to about 12.0 V at midnight (with fridge and other loads still on)

 

I havent run my boat engine for 2 weeks unless moving the boat. The quiet has been wonderful, but no idea on batt condition. I do know that the sealed batts have definately not stood up to use as well as the unsealed.

[nicknorman]

Could someone explain EXACTLY how you do an equalise charge if :

 

1. I have a gennie.

2. I have an engine

3. I have 920W of solar

4. I have a bank of 3x110AH unsealed batts connected to another 3x110AH of sealed batts (I forgot to check when ordering).

 

At the moment I'm seeing batts at a decent voltage all day due to the impact of solar, and a fairly quick descent to about 12.0 V at midnight (with fridge and other loads still on)

 

I havent run my boat engine for 2 weeks unless moving the boat. The quiet has been wonderful, but no idea on batt condition. I do know that the sealed batts have definately not stood up to use as well as the unsealed.

You need some means of charging at a higher than normal voltage. In my case I turn up the voltage on our Mastervolt Combi, fed from shore power or TravelPower (=genny). Other chargers support adjustable voltage or have a separate equalise mode, as do some solar controllers. Without some means of raising the voltage above normal charge voltage, you can't do an equalise charge.

[GUMPY]

You also have to limit current as well otherwise you cam wreck your batteries

[nicknorman]

You also have to limit current as well otherwise you cam wreck your batteries

Yes, I mentioned that in post #2. That said, and assuming your are starting with fully charged batteries in good condition, I have not found the current to be an issue, typically around a max of 3.5% of original capacity. I suspect it may depend on levels of calcium in the battery plates? Also, if a battery goes into thermal runaway when on equalise, perhaps it was already knackered?

 

Is there an accepted max current during equalise?

[Chris Pink]

Could someone explain EXACTLY how you do an equalise charge if :

 

1. I have a gennie.

2. I have an engine

3. I have 920W of solar

4. I have a bank of 3x110AH unsealed batts connected to another 3x110AH of sealed batts (I forgot to check when ordering).

 

At the moment I'm seeing batts at a decent voltage all day due to the impact of solar, and a fairly quick descent to about 12.0 V at midnight (with fridge and other loads still on)

 

I havent run my boat engine for 2 weeks unless moving the boat. The quiet has been wonderful, but no idea on batt condition. I do know that the sealed batts have definately not stood up to use as well as the unsealed.

 

An equalisation charge can only take place after your batteries are fully charged. (in your case an unlikely event). Then with your equipment the easy way is to connect one or more or your solar panels without regulator, watching voltage, current and water very carefully. (the ideals being 15.5V, 2A per battery and no water loss).

 

SmileyPete knows where to source power supplies cheaply on eBay that will do the same job.

 

As your batteries are rarely in a state of rest they are less likely to get sulphated - this happen when a battery is left in a partially discharged state. Empirical observation shows that solar goes some way to protecting batteries against it without formal equalisation.

[BargeeSpud]

 

As your batteries are rarely in a state of rest they are less likely to get sulphated - this happen when a battery is left in a partially discharged state. Empirical observation shows that solar goes some way to protecting batteries against it without formal equalisation.

 

Fascinating, I didn't realise this about sulphation, I just knew it as something that could happen & presumed it was always inevitable at some stage. I too have solar & my batteries haven't gone below 12.3v since I fitted them, so your last sentence is very reassuring.

 

Cheers.

[Chris Pink]

"sulphation" - i think it's a misleading term - is the hardening of the lead sulphate crystals that happens when they are in a state of rest.

 

It's misleading because the conversion of lead and sulphuric acid into lead sulphate is how a battery works and is an entirely natural part of the process. When the crystals become hard it is much more difficult for them to convert back to lead and sulphuric acid and that loss of active ingredient, plus the fact that they are on the surface of the plates preventing contact between the acid and lead, reduces the capacity of the battery.

 

As I say, it's empirical observations by myself and others using solar that has lead to this conclusion. I know of no formal studies of the effect of solar on sulphation but boats with solar power certainly get a lot (years) more life out their batteries.

[Christianonthecut]

Thanks,

 

The solar charge controller has an equalise function, but I was worried because they are sealed.

 

I have just set it off to run for a couple of hours at 15.5volts and 5 amps, the battery temperature is currently 17degrees, so will keep an eye on it and see what happens.

 

[Chris Pink]

Thanks,

 

The solar charge controller has an equalise function, but I was worried because they are sealed.

 

I have just set it off to run for a couple of hours at 15.5volts and 5 amps, the battery temperature is currently 17degrees, so will keep an eye on it and see what happens.

 

 

Just because they say they are sealed doesn't always mean you can't get the top off.

Further to my post above: I've just had a good google and can't find any references to studies of solar and sulphation.

[blackrose]

Presumably there's no way of doing an equalisation charge with an ordinary 12v 3 stage charger - or even 2 chargers? Mine normally takes the (wet) batteries up to 14.8v.

[nicknorman]

 

the ideals being 15.5V, 2A per battery and no water loss

 

 

Out of interest, where do you get the 2A from? (and presumably that's 2A per 110AH?). Im not arguing, just wondering if its a recognised figure or whether its just one you feel is about right.

[Chris Pink]

Extrapolated from Gibbo or Smiley Pete if I remember right. Not recognised as far as I know. I think temperature is the governing factor rather than current.

 

You're probably right, it would be a good thing to find an authorative source for but as it's an uncertain process. ie the amount and hardness of the sulphate is unknown I doubt there is one.

 

The important thing is that the battery is fully charged before it starts.

Edited June 19, 2013 by Chris Pink

[Christianonthecut]

Will have a look at getting the tops off.

 

The max 3 stage charge current is set at 50amps and of course it's unlikely it'll ever see that but I have seen 30 amps in bulk this morning. Will that be OK for my 220 (cough cough) 70aAh bank or should the max bulk charge current be limited?

Edited June 19, 2013 by Christianonthecut

[nicknorman]

Extrapolated from Gibbo or Smiley Pete if I remember right. Not recognised as far as I know. I think temperature is the governing factor rather than current.

 

You're probably right, it would be a good thing to find an authorative source for but as it's an uncertain process. ie the amount and hardness of the sulphate is unknown I doubt there is one.

 

The important thing is that the battery is fully charged before it starts.

 

Thanks. My Mastervolt Combi Equalise mode (that doesn't work very well) limits the current to 10A but since it doesn't know the battery capacity, that must be a shot in the dark.

Will have a look at getting the tops off.

 

The max 3 stage charge current is set at 50amps and of course it's unlikely it'll ever see that but I have seen 30 amps in bulk this morning. Will that be OK for my 220 (cough cough) 70aAh bank or should the max bulk charge current be limited?

50A into 220AH is OK, into 70A is rather a lot but hopefully you will recover them back to 220AH. I'm not sure its a big factor in battery life though - we have a 175A alternator into 440AH and that seems OK, although it comes out of bulk pretty quickly (ie current falls below 175A). Its probably better to charge the batteries slowly, if possible and in an ideal world, but if you are burning fuel to do it, there has to be a compromise.

[Christianonthecut]

Thanks Nick, will leave it as is for the time being. When the controller asked for the bank capacity it limited the max current to 22 amps, but In wanting to see what the set up is capable of I adjusted it to max amps.

 

50 mins to go and the battery temp has risen to 21C.

[Chris Pink]

 

Thanks. My Mastervolt Combi Equalise mode (that doesn't work very well) limits the current to 10A but since it doesn't know the battery capacity, that must be a shot in the dark.

 

Is that user adjustable or a fixed amount?

 

It sounds reasonable to me. I am guessing that Mastervolt, like Victron, would have made recommendations for minimum bank size to run the inverter (somewhere around 450-500Ah)

[smileypete]

Since I've been mentioned I'll chip in with my 2p worth...

 

First off with anything to do with batts is to follow safe handling procedures, which can be found on The Battery FAQ, and elsewhere via google:

 

http://www.batteryfaq.org/

http://www.leadacidbatteryinfo.org/lead-acid-battery-safety.htm

 

This is a MUST as as exploding batts can seriously injure unprotected eyes and faces. The individual MUST fully understand and mitigate the risks and accept responsibility for ANY outcome. If not then stop reading this now and leave well alone

 

Before eq batts need a FULL charge and then topped up to the correct level for unsealed. If the batt is suspect in that it won't hold a charge, charge current never tails off below 3% of batt capacity, or shows an abnormally low or high 'resting' voltage, then best leave well alone. Just before eq it's probably a good idea to undo the batt caps, and leave them just resting in the holes if they're not the water saving type.

 

Now, when equalising batts it's always best to follow the manufacturers recommendations, trouble is with all these off-brand el cheapo leisures is there may be no information available.

 

If so, for unsealed leisure batts probably the next best thing is to see what the likes of US Battery, Trojan, The Battery FAQ recommend:

 

http://www.usbattery.com/usb_faqs.html

http://www.trojanbattery.com/BatteryMaintenance/Equalizing.aspx

http://jgdarden.com/batteryfaq/carfaq9.htm#equalization

 

From all the above a general recommendation for an unsealed 12V batt could be an eq of 15.5V at 25°C, for 4 to 6 hours, with the current limited to 3% of batt capacity, and the temperature of the batt kept below 40-50°C. If the temperature is higher than 25°C the eq voltage is reduce by 0.03V for each degree C extra, and vice versa for lower temperatures.

 

For sealed 'maintenance free' leisure batts it's very tricky as they can't be topped up, can get abused, and be quite fragile. Personally I'd increase the eq voltage a little to 16V but limit the current down to 1% of batt capacity.

 

For something to generate the eq voltage and current, a lab power supply with current limit, or a DC-DC converter with constant current (CC) control would be ideal, these look pretty promising.

 

http://www.ebay.co.uk/sch/i.html?_sop=15&_sacat=0&_from=R40&_nkw=600w+dc+converter&LH_PrefLoc=2

 

Failing that a fixed voltage supply, converter, or solar panel could be used with resistors or bulbs to limit the current and batt voltage to safe levels. But it then needs constant monitoring to ensure the eq voltage and current stays at the right levels.

 

Of course as with connecting any extra stuff to the batts an appropriate fuse must be fitted in the positive near the batts, but outside any batt box.

 

Happy eq charging!

 

cheers, Pete.

~smpt~

Edited June 19, 2013 by smileypete

[Christianonthecut]

Thanks Pete.

 

I will monitor AH's used against voltage readings again and see if matters have improved.

 

Failing that I'll set the charge controller to EQ at 16volts for 6 hours at 2amps and then consider buying a set of Trojans.

[BargeeSpud]

Since I've been mentioned I'll chip in with my 2p worth...

 

First off with anything to do with batts is to follow safe handling procedures, which can be found on The Battery FAQ, and elsewhere via google:

 

http://www.batteryfaq.org/

http://www.leadacidbatteryinfo.org/lead-acid-battery-safety.htm

 

 

I've had a printed off copy of the Bill Dardon FAQs for a few years now & it was well worth the effort, It's a briliant piece of reference. I've not seen the next link you've posted before, but I will also print that off to keep on the boat as well.

 

I'm going to go away & check out the other links & print off any I want to keep.

 

Thanks for putting those up.

[nicknorman]

 

Is that user adjustable or a fixed amount?

 

It sounds reasonable to me. I am guessing that Mastervolt, like Victron, would have made recommendations for minimum bank size to run the inverter (somewhere around 450-500Ah)

Fixed amount. The manual doesn't specify or recommend a bank size, though I suppose you're right that there is a fairly limited range of "reasonable bank size". When you trigger equalise, it gradually ramps the voltage up towards 15.5 (temp compensated). It doesn't do it by current limiting (since the current doesn't normally get to 10A), but presumably by time. The spec says max equalise time is 6 hrs but I find it auto-exits the equalise mode after typically 30 minutes, not quite sure why. Therefore, rather than repeatedly triggering equalise mode, I prefer to just set the absorption voltage high (it can be set up to 16v, temp compensated) using the Masterview screen which is connected to the Combi and the Mastershunt and allows hours of endless fun fiddling with it! The MV main screen is set to display, amongst other things, battery temperature and current, so I can keep an eye on it.

As I've said on a different thread, I'm amazed how much capacity is lost in normal use, and then regained by equalise, even though the batteries are only ever used over night and fully charged the next day, or left on float when we are away from the boat.

[smileypete]

Thanks Pete.

 

I will monitor AH's used against voltage readings again and see if matters have improved.

 

Failing that I'll set the charge controller to EQ at 16volts for 6 hours at 2amps and then consider buying a set of Trojans.

 

Yeah if you can do the eq it's hard to go wrong with the Trojan or US Battery 6V jobbies

 

cheers, Pete.

~smpt~

[by'eck]

Equalisation charge of battery(s) refers to forcing a charge current into the battery at a higher than normal voltage to attempt to break down the sulphate crust that may have formed on one or more of the cells, and so preventing them from taking a charge. The result is to bring all cells back to the same sulphate free state, hence the term.

 

In practice this will do little to improve the good cells which will gas more than normal and very likely require the electrolyte topping up. It shouldn't therefore be undertaken with anything other than open lead/acid batteries. The process should be performed with all loads disconnected to avoid possible damage to them.

 

As nicknorman mentions you can wind up the charge voltage on a Victron to achieve this. Sterling Combi's have a dedicated de-sulphation (equalise) mode that takes the batteries up to 15.5 volts with a caveat that it should only be undertaken with open-lead acid batteries, and then only for a limited time with constant monitoring (cycle is automatically limited to 4 hours). Their CED chargers (and probably others) have an auto-equalise mode every 15 days although I think this may be tempered by the selected battery type since no figures are mentioned.

[Proper Job]

 

Yeah if you can do the eq it's hard to go wrong with the Trojan or US Battery 6V jobbies

 

cheers, Pete.

~smpt~

wiring up 4 x 6v 105's makes a nice tidy install as well. One cable in, one cable out and four link straps of the same length - job done

 

450 Ah battery bank (@ 12v)