6V GOLFCART BATTERIES

[nornaj]

We recently replaced the original Group 31 FDCs on our SO39i with 6 x 6V US 2200 FDCs. They have an aggregate rating of 696Ah. Based on an initial efficiency rating of 75% for new batteries, a usable figure for the Ah should have been at least 260Ah or, more wishfully, the full 348Ah which is what we are looking for in the long run.

Initial cycling produced surprisingly poor results. 200Ah from fully charged to 50% as indicated by SG (1190). At that stage the panel was showing 11.7/11.8 and the Xantrex Linklite was showing 12.0. Letting the batteries rest for several hours resulted in about 12.2 volts measured at the batteries.

Having subsequently cycled the batteries twice more, it appears that things are improving marginally.

At completion of the last cycle, however, and using a "better" hydrometer, there are significant differences between the SGs of individual cells. Golfcart manufacturers (e.g. Trojan, US) recommend an equalization charge to resolve this problem. And then, helpfully, state that "Many chargers do not have an equalization setting so this procedure cannot be carried out." NornaJ is fitted with the original Cristec 40A OEM charger which, as far as I can see, does not have an equalization setting.

Normally, we leave the shore charger on whenever shore power is available, and throughout the winter months. At least one "expert" website says that this the wrong thing to do. In addition, it suggested that if the charger is left on ".. it will equalize your batteries to death."

I guess the questions are: If we leave the shore power charger on for a lengthy period will it equalize the batteries? If not, do we have to replace the Cristec with charger that has an equalization setting?

Advice will be much appreciated.

Norna J

[ubuysa]

I don't think your mains charger is man enough for those batteries. You want your charger to be able to output least 10% of the total Ah capacity of your batteries, more if possible. So you need a charger that can output at least 70A, ideally 100A would be best

I think you'll find you're just not charging those batteries properly with that charger.

[Mistroma]

Ive had 4xTrojan T105s (450Ah @ 12V) fitted since April 2012 and no need for eq. charge yet. Max. SG diff was 0.025 but came back to 0.015 on next check. That's only on one battery and others are still within 0.005 variation cell-cell.

I've not found any problem keeping batteries in decent state with Cristec 40A charger and a fair amount of time at anchor. That's after 2 full seasons so far with boat in water for 6 months each year and laid up ashore for remainder. The OEM charger doesn't have eq. setting (though you can alter the Voltage with a bit of tweaking). My 40A unit is just about OK with 450Ah and I'd need a min. of 60A charger with 696Ah.

I realise that usage has a big impact so have added following to let OP compare with his likely type of use.

Batteries never cycled below 50% and rarely below 60%. They had an especially easy time in 2011 as we spent a lot of time in marinas and on move most days with decent charge from engine almost every day after we left a marina. However, a lot of 2013 was spent at anchor (approx. 76%).

2012:
Winter charging via 65W solar panel
Normal system 65W solar panel, Rutland 913, 40A mains charger fed from shore power or Honda 20Eui generator
Days in marina 112 (Lived on board for 2 weeks n UK & left boat in France for 2 weeks mid-season)
On move most days batteries always well charged in marina & during day.
Only at anchor 38% of sailing season

2013:
Added more solar to give 145W (Revert to 65W panel for winter)
No other change to system
Days in marina 43
Most marina time at beginning & end (14 days pre/post sailing)
At anchor 76% of sailing season

[Mistroma]

A few more specific points relating to your query

1) Trojan say that max. capacity of T105s develops over first 50-100 cycles. Perhaps capacity will continue to rise on your set.

2) OEM Cristec shouldn't boil your batteries unless you use wrong settings (you can turn off boost & reduce V over winter to 13.2V)

3) If you are mostly on mains power then charger is only putting in a few A when boat not in use (~3-5A) so capacity not an issue

4) Large capacity only relevant for early stage of charging up to ~85% (hence comment 3 above)

5) I think a 40A charger would be OK for Eq. charging as current won't be that high (prob. ~15A for 696Ah bank, check with mfr)

I haven't tried to use a Cristec CPS2 for eq. (might be possible) but all items would need to be disconnected to prevent damage. One setting will give 15.1V and I think that this can be adjusted (via internal pot.) to 15.6V required for eq. charge. I'd obviously monitor voltage, current and battery SG during the process if I decide to try it. SG differences are still acceptable on my set so it looks as if I might only need eq. once a year with my usage pattern.

[electricmonk]

"Normally, we leave the shore charger on whenever shore power is available, and throughout the winter months. At least one "expert" website says that this the wrong thing to do. In addition, it suggested that if the charger is left on ".. it will equalize your batteries to death."

With your charger this cannot happen, after a bulk charge it will fall back to float voltage which varies from around 13.2v - 14.8v depending on the type of battery selected on the charger or another value set by you.

However, when first switched on the charger does a boost charge for around 6 hours and this is in many ways similar to an equalisation charge. The advice is to disable the boost setting if the mains supply is unreliable.

Even with golf cart batteries ( which are only basic lead acid technology) its a good idea to keep them above 50% discharge for longer life.

In case you dont have it look here for specs on charging currents and voltages, note the comment that float charge voltage can be applied indefinitely.

www.usbattery.com/usb_images/usb_2200_data_sheet_2013e.pdf

these are C20 batteries so you don't need a fairly hefty charger - 70 amps possibly (for the whole bank) your balmar might be a bit too big.

Doing some calculations on your set-up the realistic usable capacity (after one night at anchor) will be around 200AH assuming you can get them to 85% and not let them drop below 55% - its all about charge absorption rate. I doubt you will be motoring for 30 or so hours, which is where you need to be to get close to 100%.

Capacity at 55% discharged = 383AH

Capacity at 85% charged = 592AH

Subtract one from the other and we get 209AH

sorry about the figures but they are the facts, and please no more maximum discharge tests :-)

[nornaj]

Thank you all

The cell variations are greater than the ones you have experienced, Mistroma. i.e. 0.040 at "full" charge and 0.045 at 50%. That seems to call for an equalization charge. Noting that they have only experienced three cycles so far.

I had missed the note on the US 2200 spec sheet that float charge can be applied for an unlimited time. Thanks electricmonk. Also good to know that the Cristec will not "equalize the batteries to death".

Taking into account our usage pattern, I think the Cristec 40A shore charger has sufficient capacity. In the worst case, 50% discharge, we would probably need 12 hours plugged-in to get back to nearly full charge allowing for onboard DC usage.

Will review the Cristec manual some more to see if the unit can be re-jigged for equalization.

NornaJ

[electricmonk]

"Taking into account our usage pattern, I think the Cristec 40A shore charger has sufficient capacity. In the worst case, 50% discharge, we would probably need 12 hours plugged-in to get back to nearly full charge allowing for onboard DC usage."

The above implies a constant average charge rate of 33 amps for 12 hours and assumes a charge absorption efficiency of 100% - life's not like that.

As the batteries charge the rate of charge tapers off this is most pronounced after 80%, AND the amount of energy you put it is massive compared to the amount that is stored i.e. efficientcy plummets. (the smart regulator guys are a bit reticent on this basic property of the lead acid cell be it sealed flooded gell or AGM) - but your Balmar will get to 80% a bit quicker than the standard offering - but not much in the grand scheme.

To reach anywhere near 100% will take at least 30 hours of charging with no load on the system a situation we only see when we leave the boat connected to shore-power with all loads off or with the batteries on a bench. Solar helps.

sorry


As soon as you leave the dock you are in the 80 - 85% band of your capacity unless you run a charger all the time that can cope with recharging and the load (which is what your car does, and why automotive alternators have grown larger over the years its about load not recharging) so in many respects a very large battery bank is a liability not a asset.

[ubuysa]

I'm no expert on this but I've spent some time in the past talking to those who are.

At 50% DoD your batteries require just over 200Ah to bring them up to 80% DoD. Wet cell batteries like to be charged hard, and as hard as you can, so you need a charger that can get them from 50% DoD to 80%DoD as quickly as possible (and not just for your convenience but also for the best battery life) and that means using a charger that can supply as much current as the batteries can accept in the Bulk stage. Once 80% DoD is reached the charger will switch to the Absorption stage and the current will fall. Your charger will take over 5 hours to reach 80% DoD even supposing it can supply 40A continuously (which it probably can't) and that's too long, I'm pretty sure you'll find your batteries could accept a much higher current than 40A during the Bulk phase.

I really do think you'll get better life from your (expensive) batteries and a quicker charging cycle by upgrading to a charger with a minimum output of 10% of the Ah capacity of your batteries. As an example we have 330Ah of house battery capacity and a 45A charger, my tame electrical expert tells me that even this could do with being bigger.

Those batteries are good and expensive so I really would seek some expert advice on that charger.

[electricmonk]

Nov 10, 2013 8:04:16 GMT ubuysa said:

I'm no expert on this but I've spent some time in the past talking to those who are.

At 50% DoD your batteries require just over 200Ah to bring them up to 80% DoD. Wet cell batteries like to be charged hard, and as hard as you can, so you need a charger that can get them from 50% DoD to 80%DoD as quickly as possible (and not just for your convenience but also for the best battery life) and that means using a charger that can supply as much current as the batteries can accept in the Bulk stage. Once 80% DoD is reached the charger will switch to the Absorption stage and the current will fall. Your charger will take over 5 hours to reach 80% DoD even supposing it can supply 40A continuously (which it probably can't) and that's too long, I'm pretty sure you'll find your batteries could accept a much higher current than 40A during the Bulk phase.

I really do think you'll get better life from your (expensive) batteries and a quicker charging cycle by upgrading to a charger with a minimum output of 10% of the Ah capacity of your batteries. As an example we have 330Ah of house battery capacity and a 45A charger, my tame electrical expert tells me that even this could do with being bigger.

Those batteries are good and expensive so I really would seek some expert advice on that charger.

All the information required to size a charger is in the data sheet. See my previous posts its all in there.

I don't call myself an expert but was factory trained in auto electrics and contributed to the design and installation of systems on passenger vehicles, trucks, gen sets, race and rally cars and boats for about 12 years.

The maximum bulk charge rate for these cells is 10% of the C20 AH Capacity - that's 23 amps, you have three banks so in accordance with Kirchoff's law we can supply 3 x 23 amps for the bulk charge 69 amps hence my suggestion for a 70 amp charger and the comment that 100 AMP may be too big.

Let's assume that battery charging efficiency is 70% (its a good average for any lead acid cell technology up to 80%) and everything is in tip top condition.

So assuming you can charge at 23 amps constantly it will take around 7.2 hours to reach 80% - the charge rate then drops to absorption rate 3% of the C20 AH Capacity (7 amps). Hence it will take a very long to get the last 20% - another 15 hours or more as charge absorption tapers off.

In reality you wont get 23 amps for 7 hours hence my suggestion that 30 hours is a realistic time for a 100% charge without frying the batteries.

The above is why I suggest you don't let the cell drop below 55%, 5% at that end of the process knocks hours off the recharging time to reach around 85% which as I said before is the best you can get unless you run the engine all day long.

A small (100 watt) solar panel deployed at anchor will dramatically enhance your endurance and reduce your engine hours recharging to maybe every other day.

My boat has a standard 80 amp alternator, standard diode splitter and 50 amp shore power charger. 3 x 100 AH wet cell batteries in the house bank and 1 x 100 AH wet cell starter battery. To keep up with load at anchor I have an 80 w solar panel I tie to the coach roof. If the batteries get low (12.2v) I start a 4 KVA generator. I get about 8 years out of a set batteries all I monitor is battery voltage EASY! - but then what do I know?

[rxc]

My T-125s are now 6 years old and doing quite well. I don't think I have ever equalized them, but they do have two solar panels and a windmill keeping them charged as well as the 40 amp charger.

I think the most important item to remember is keeping them filled with water. Since I have the solar panels, they are always on float, and I notice that they use quite a bit of water. With the solar panels the float voltage is a bit higher than optimal - 13.7v (even with a solar controller) - so this causes the batteries to outgas. I just put the boat on the hard in the US while I move house from France to the US, and I had to add a considerable amount of water. This is after topping them up in the spring, and not using the boat at all this year, except for two short delivery cruises.

I have also replaced two group 31s that were installed at the same time as the T-125s, and which are essentially charged in parallel with them. They lasted 4 years as the engine starting battery and the windlass/bowthruster battery. The 31s were sealed, so that I could not check/add water to them. I would not be surprised to find out that they had dried out.

Next time I replace these two batteries, I will really search for ones that can be refilled with water. I have considered hydrocaps, but they are expensive, and forcing myself to check water levels is one important maintenance item that I think is too important to leave to an automatic device.