New 60Ah gel battery cycling?

[T i m]

Hi All,

I have on approval a new MK M34 SLD G, 60Ah (20hr) gel battery

the intention of using it on a small electric outboard motor.

know I can get higher capacity batteries for about what I'm likely to pay for this but I believe the gel batteries (when properly looked after) outperform most other types re number of cycles.

So, I charged it up with one of these:

then discharged it with a 12V car fan heater that draws about 10A.

On the first run it took about 2 hr 15 min to reach 10.5 volts and yesterday about 2.5 hours (cycle 2).

Last evening, after showing charged on the Draper charger I stuck it on the Optimate and left it charging overnight:

about 4 hours was still charging and this morning it was showed 'charged'.

I ran my discharge test again and this time it ran for 3hr 15min. It's been charging for about 6 hrs and is currently 2.5A (but I'm not sure if my DMM influences that) and 13.5V.

Now I think I read somewhere these sort of cells can need around 15 full cycles before they come up to spec but I was wondering what sort of improvement was considered typical?

Also, what would be the best charger for this battery. On it's spec it suggests the full on-charge voltage should be between 13.8-14.1V (at

68°F) but even the CTEC Multi XS 3600 suggests it charges up to 14.4V? [1]

'm not sure I like the 'most' in "14.4V/3.6A Normal setting for wet batteries, MF and for most GEL batteries".

I've made contact with MK UK but am yet to talk to the tech guys.

Any thoughts or ideas or input welcomed. ;-)

Cheers, T i m

[1] I've just checked the spec sheet with the Aldi / Medion MD 11265 charger and it also goes to 14.4V but suggests it's ok with gel batteries?

[John Weston]

being overcharged and, as you say, you'll need to look after it. :-)=20 "Intelligent" can be a misnomer, IMO... I've a similar charger but of=20 different make, which I've dismantled to fix a fault and the electronics=20 show little signs of any "intelligence". OK for a wet car battery, but=20 a deep discharge type confused it...

But your motor is drawing more than 40A, so the battery will supply this=20 for around 60mins to flat or around half this if you want it to last. =20

10.5V is discharging it too far, risking sulphation. if you want it to=20 last, you shouldn't go much below around 50% capacity, see:=20 A gel can take=20 going lower but it's a risk and 10.5V is off the scale. You'll need to=20 recharge it immediately to rescue it, which is practically difficult.

batteries, and it seems to do wonders with deep-discharge, 1-200AH=20 batteries that I'd previously had to replace, so it's paid for itself.=20 It's specified to work with Wet, MF, AGM and Gel from 50-500AH

I don't think your choice would be a problem for your gel, since it's=20 main charging, "Bulk" cycle, is effectivley a 3.6A constant-current mode=20 where the charger voltage gradually increases to maintain the current. =20 At 3.6A it's going to take a long time to reach the 80% charged level,=20 so I don't think you'll be harming your gel battery, as you'll be=20 charging it at C/16.=20

To charge above the 80%, it switches to "Absorption" mode, which is=20 constant voltage with a reducing current, starting at the bulk's C/16=20 rate and dropping as the battery accepts the charge. This phase stops=20 when the current falls to a preset level.

--=20 John W To mail me replace the obvious with co.uk twice

[meow2222]

I didn't think so. Gel cells are a compromise design. Consider the failure modes.

14.4v is great for wet cells, but way too high for gels. 13.6-13.8 is right for gel.

NT

[Dave Plowman (News)]

I know I can get higher capacity batteries for about what I'm likely

Don't think so. Most deep discharge types are wet.

And then discharged it with a 12V car fan heater that draws about 10A.

require constant voltage charging.

I've never heard of lead acid needing cycling to give their best from new

- although read it about Ni-Cads. But not even sure this is true there.

No. SLA require constant voltage charging - and that voltage should be

13.8. To avoid damage. A wet battery can gas if overcharged - not so with a gel type.

You could charge them at a higher voltage and therefore current to start with within reason, but not as they approach full charge.

[T i m]

>I wouldn't use one of these on a gel battery since they do not like

Well I haven't seen anywhere near the final voltages that I've read on the datasheet so I thought (hoped) it was under rather than over-charging? The max current seems ok and does seem to taper off ok at least.

Understood, mind you, they do discrete chips for such roles so it wouldn't need that much around it to make it all work reasonably well (if designed properly etc).

This one certainly confuses my Gold IBT capacity tester. It repeatedly thinks it's a 13Ah!

The littlest model (M12) suggests it's only 30A (FWIW it draws under

2A in the air at full speed but I'm not making an air-boat ) but you may well be right in practice.

Also ... if I've got this right and according to their data at 100% discharge (so down to 10.5v?) these cells still should ~500 cycles. If I take the outboard out 10 times a year ... ;-)

Hmm, I was sorta going by the manufacturers guidelines:

the 8G34)

Does that only differ from is smaller brothers by having the PSU feature and the facility to avoid stratification, not something I believe affects gel batteries in any case? As I also have quite a few smaller batteries in use (motorcycle etc) the smaller model would probably be more use to me (and cheaper). ;-)

Ok, this is supposed to be the rules:

At 3.6A it's going to take a long time to reach the 80% charged level,

Understood.

Understood, so apart from the switch off bit could I not do all the above with a current limited variable voltage bench PSU? I have a Kingshill 5A/30V jobby that would do such? (Set offload voltage to

13.8, set current limit to 4A, turn off manually when current drops back to little?).

So, would the CTEC looking jobbys that often come with the mobility buggies that these batteries are typically used with these days be that clever / expensive?

Cheers, T i m

[T i m]

That's near to what MK themselves suggest (at 20 deg C), 13.8 (->

14.1V MAX).

I'll be interested to see what tomorrows test brings.

Cheers, T i m

[Fredxx]

That's fine for float charge where a charger is permanently connected. Be careful of temperature, the higher the temperature, the lower the voltage should be.

That'll be for charging where charging will stop at a predetermined voltage and drop back to at least the float charge voltage as above.

14.4V is for charging a wet cell, and certainly not for permanent float charge connection, even for a wet cell.

[T i m]

Understood and many (most) of the better / intelligent chargers have temperature compensation.

Understood. The charging voltage for this battery is given(by the manufacturer) as 13.8-14.1V and float as: 13.5-13.8V

Understood and why I was reticent to use any charger I've found so far that lists gel compatibility yet offers a peak charging voltage greater than 14.1V.

Bottom line, by using a low current charger with a tapered charging voltage should mean that by the time the charge cycle has reached anything like the maximum voltage for the battery the current will have dropped back to a sufficiently low level to prevent gassing.

Until I get any further confirmation from the manufacturer regarding approved chargers or confirm techniques I'm going to stick with the Draper jobby because it specifically states:

"These chargers are suitable for all 12v lead acid batteries. For Gel Filled and Other Sealed Batteries use BCI model only."

Which is the model I have.

It also supports a maximum battery capacity of 60Ah (mine) so would charge it at the lowest rate.

The instructions go on and seem to understand the requirements of a gel battery:

"Gel Filled and Other Sealed Batteries (Use BCI model Only) This type of battery normally contains gel electrolyte and may be referred to as ?Dry Fit?. They are most commonly used in applications such as, electric golf trolleys, mobility wheelchairs, camping, caravanning and marine activities, etc, (see below). To charge this type of battery we strongly advise you only use the Draper intelligent Charger (BCI), which is fitted with temperature sensor compensation which allows continuous adjustment of the unsupervised charge to ovoid overcharging and loss of electrolyte by ?gassing? which can shorten the life of the battery.

Once the battery has reached capacity the intelligent charger will automatically avoid overcharging by continuous adjustment and temperature sensor compensation of the unsupervised charge to maintain near 100% capacity."

Cheers, T i m

[Dave Plowman (News)]

How do they obtain that from the battery?

[T i m]

Quite possibly, however why would that preclude that size for size the gel batteries don't (for example) last longer? (I didn't meant to suggest 'in every aspect' when I said 'out perform'. I was thinking of life span in my usage). ;-)

Understood, however is a very low current and fairly sophisticated charger. Update on the that. The fist time I pot the Optimate on after the Draper had indicated it was fully charged it stayed 'charging' for quite some time. I took the Draper off yesterday then attached the Optimate and it showed charged very quickly (FWIW etc).

"The most obvious indicator of a quality deep cycle gel battery is that it requires 15-20 cycles before reaching full capacity".

And over the 3 cycles I have done so far the capacity has increased each time. . In fact the reason why I'm doing this is because this is it's supposed to be a brand new battery but has been sitting about for ~ 6 months. I was intrigued to test it's capacity (something I used to do regularly with whole batches of std SLI batteries when I was using them for racing) to pick a good matched pair.

Understood and why I was / am wary of any charger that purports to cover all types. If you really had a constant voltage wouldn't the initial charge current only be limited by the internal resistance of the battery and the ability of the source (for the bulk phase at least)?

I have used my bench PSU as a charger on many occasions. Set the peak voltage and current limit and off it goes. As soon at it reaches peak voltage the current backs off down to nearly (normally) nothing.

I've taken the charger off so I can let the battery stand and measure the standing voltage pre another discharge cycle which I will start later.

Cheers, T i m

[T i m]

I don't think most of them can can they, it's just 'ambient', possibly even at start?

I have RC chargers that have a sensor on the actual cell so it can be done more accurately.

T i m

[Dave Plowman (News)]

It also mentions memory effect...

I'm not saying it's not the case (because I don't know for sure) with some batteries - but at least some makers must cycle them at the factory so they are at peak performance when first charged and used.

[Fredxx]

It has always taken a few cycles for the correct amount of lead compounds to form on the plates. I've forgotten the exact chemistry.

[meow2222]

as said before, consider the failure modes. Then you'll immediatey see that the only thing a gel electrolyte does is add more failure modes.

That is not the point. If it charges wet cells it will put out too much voltage. Period.

patent marketing baloney. All lead acids do this, as the plates are microscopically etched during cycling, increasing their surface area.

You need one specifically for SLA batteries. Otherwise the cells will see much too much voltage and die young.

NT

[T i m]

And a greater number of cycles.

This seems a reasonable overview of the situation:

>>> Understood, however is a very low current and fairly sophisticated >> charger. >

Q. How much damage would a 1000 volt / 1mA charger do to this battery?

Ok. I have since found an answer to my actual question and the 'improvement' to a battery because of this process is only about 5% (which would be the right sort of order of magnitude given your description of why).

Can you find me one out there then please (for 12 not 24V and sub £75!)? Pretty well everything I've found so far that is 'intelligent' states (amongst all the others) 'gel' ?

And further, it seems that many also state the charging voltage of

14.4v but therefore take it higher than data sheet for the battery I have here suggests it should be (14.1V max).

T i m

[Dave Plowman (News)]

disseminating facts, though.

The accepted way of charging an SLA is constant voltage - and that voltage is 13.8. I'm sure you could make a more sophisticated charger and blind everyone with science - but in the same way as constant current charging at 1/10th the capacity works best for long life with Ni-Cads so does using the old method for SLA. And like all lead acid, the less it is discharged before re-charging, the longer the service life.

A half decent way of checking claims for any particular make of battery is to look at the warranty. Is it any longer than others of a similar cost?

[T i m]

;-)

So why do so many charger manufacturers state 14.4V?

No time, no interest, I just want to buy something affordable that will get the best out of the battery.

I'm not sure how far back you are going with 'old method' but the key with gel particularly (unlike NiMH etc) or wet cells is what happens when you reach the overcharge state. A nicad just get's hot, a wet cell gasses but a gel causes bubbles to form, holding the electrolyte away from the plates, reducing the capacity (crudely etc).

Of course. However, I want to run an electric outboard and I want it to be practical / fun. I don't want to *just* discharge the battery down to 50% because to do the same job I'd have to carry a battery of twice the capacity and they are heavy enough as it is. Also I don't care how long it takes between charges because we are unlikely to be using the boat again till the next day at the soonest. So, I know I'm going to cane the battery in actual use but I wanted to give it the best chance whilst charging. That means charging it fully (not over or under) and at a sufficient rate to do the chemistry / charger justice.

However, I'm not about to spend £200 on a charger for a £70 battery (£133+ retail) and even finding a VFM one that isn't expecting 2 x 12V (for the mobility / golf buggy trade) isn't easy.

Not sure, not been offered any to compre it with. ;-)

I was looking for 'a battery' to use with my new outboard and rang my mates at the mobility shop. They 'happened' to have this particular battery spare and owed me some favours. Had I not got that I have an Auto electrician mate who can get 40% discount on std 'leisure' batteries at similar money but I already have a stack of them waiting to go to the dump that have mostly died from being unattended.

Gel seem slightly better in this area as well.

T i m

p.s. I've email CTEC to ask if they would recommend a charger for this specific battery.

[meow2222]

none. Thats not what you have though.

Its far more than 5%, as you've already found by experiment. You could also determine that visually by looking at the surface of an etched plate under a microscope.

unfortunately no, its been a long time since I bought a lead acid charger, so I dont know what's on the shelves now. Why not make your own, theyre pretty simple. Just a voltage limited current limited power supply would do ok, as long as you disconnected it once done or add a timer.

all wet cell chargers will mis-charge a gel cell. AFAIK there's no way a charger can test its load to tell if the battery is wet or gel.

NT

[Fredxx]

I doubt much damage will occur if the charger was a 14.4V one. The crucial thing is what the charger does once it gets to 14.4V. If the output drops to the float charge voltage I would be happy with that. If it sits at 14.4V indefinitely then that's a big no-no. Even wet batteries will lose a small amount of fluid over a period. You should be able to calculate the rate of water loss by measuring the current.

[Fredxx]

The only trouble with 13.8V as a charge voltage is it will take a long time for the battery to get to full capacity.