Battery charge current vs voltage?

[VicS]

doom and gloom, batteries knackered if you let them go tooo low, load of bollox

The life of a battery will depend, among other things, on the number of cycles it is put through and the depth to which it is discharged. Some battery manufacturers even quote typical life expectancies in terms of number of cycles for the various batteries they offer based on those two parameters.
Batteries intended purely for engine starting will not tolerate a huge number of cycles down to 50%, leisure batteries will tolerate more. True deepcycle battereis will tolerate a considerable number of cycles and can be discharged routinely to below 50%.

Delayed recharging of a partially discharged battery is another factor that will reduce its life expectancy.

 

[halcyon]

Thanks Brian

I've just realised I would be reading the regulator voltage and not the battery voltage when charging. I looks like I will have to spend £100 on an ammeter and shunt after all.

Jim

Get in touch before you spend that sort of money, can save you some.

Brian

 

[Allan]

Can I add a question to this thread? I will be changing my batteries soon. Should I go for 2xTrojan batteries, 225Ahrs, 1300cycles and £250 or 2xstandard leisure batteries plus monitor system, 220Ahrs, 100 cycles, £220? Adding the monitor to the Trojan budjet would go over budget.
Allan

 

[mitiempo]

Which Trojan batteries are you referring to? Their 6 volt T105 is 225 amp hours. 2 of these will give you 225 amp hours @ 12 volts. Not sure where the 1300 cycles comes from though. These are probably the most durable 6 volt batteries available at a reasonable price.

 

[mitiempo]

Allan
Here are the charts from Trojan listing the specs and life cycles. The cycles are in the right column. The Trojan battery that withstands the most cycles is the T105, which is also the only 225 amp battery. The life cycles are 754 for this battery. The only 12 volt Trojans that comes close are the J185 and J185HC at 600 cycles and these are very heavy batteries at 216 and 239 lbs respectfully. These are cycles to 50% state of charge. Just curious where you got the 1300 cycles from.

 

[Allan]

The figures were given to me by a supplier, I will be ringing him this week to find out if it was my mistake or his. Many thanks for pointing that out. The reason for my question was to decide if it was better to pay for a monitor or better batteries?
Edit, Yes it was the T105 we were talking about, we also discussed the T125. I wonder if he was adding the cycles together as they would be in series. I'm sure this would be wrong.
Allan

 

[mitiempo]

Allan
He probably was adding the cycles but you're right, that is the wrong way to do it. Trojan are very respected and the T105 is considered the best value in a top battery in North America, if not worldwide. I have nothing bad to say about them and will be buying 2 in the spring for a 225 amp hour house bank myself. As you can see from the charts they are the longest lasting Trojan battery, even longer lasting than the T125 and T145 of the same type. There are people I know who have had T105 banks lasting 8 or 10 years with proper care.
I think the best solution is to buy a good battery like the T105 and a monitor to help you take care of them. Iy is my belief that the monitor should be the first upgrade to a system. It will get rid of bad usage and charging habits and give you a good handle on your system - no more guessing. If on a budget and you need batteries I would buy the Trojans and save up for the monitor. I have a Xantrex Link 10 but the Victron BMV-600 is a great monitor and over here it's the best value right now. Hope this helps.

 

[halcyon]

Can I add a question to this thread? I will be changing my batteries soon. Should I go for 2xTrojan batteries, 225Ahrs, 1300cycles and £250 or 2xstandard leisure batteries plus monitor system, 220Ahrs, 100 cycles, £220? Adding the monitor to the Trojan budjet would go over budget.
Allan

It depends on your use on battery type.

If you used your boats for 2 months a year, each day you used 50% of your battery capacity, the it would take you 10 years to reach 600 cycles.

If you have a electic vehicle that you use 5 days a week, you reach the 600 cycle in 2 years.

So work out your planned usage, then how long you want to keep the boat, then select a battery type that matches.

Battery monitoring, a very grey area.

What is a full battery, you need this to say what your percentage capacity is.

So voltage/recharge voltage level is used,
but it varies with type/make of battery, it even varies with the same make/type of battery, it varies with age ( a new battery full charge voltage rises with charging, peaks and then falls with age ) it varies with how it has been looked after, it varies with temp, air pressure. Then when you check the voltage, does the fridge/bilge pump cut in, giving a false reading, does the sun come out and the solar panel start working, the list of variables goes on.

How to check usage,
Measure battery voltage ? same problems as above, at what point do you measure voltage, what load from perminently live feeds, they drop some voltage.
Measure current, but you have a tolerence on the shunt, it will vary with temp, you are measuring very small values ( 100 amp 50mV shunt equals 0.005 volt for 10 amp ), so you can have volt drop problems on all connections, plus picking up stray voltage.

So most battery monitoring can only give a guide.

So just watch charge volts, once you reach your peak voltage, watch your amps, they will remain constant at first then start to fall, once you reach a point that you thing is not enough, you are fully charged.

Measure net amps at battery, not alternator.

Watch the volts in use, and amps, running a load of 1/20 battery capacity, 11.85 volt is around 50% capacity, so recharge before you get there.

No load. settled battery. 12.35 volt is around 50%.

Full could be anything from 12.7 to 13.2 volt, so do not try to be accurate


Bottom line answer, fit the cheapest battery to meet your needs, and watch your volts and amps.

Brian

 

[Plevier]

Willow
The chart I posted was for a specific Trojan 12 volt battery and you can say that as Trojan did. I didn't say it would be precise for all but close. I agree a monitor is by far the best way as without one you have to rest the batteries before checking voltage - not really practical in real life. A battery monitor tells you what is more important than voltage in reality - state of charge or % of charge. As well as amps in or out. And I think you'll find a battery monitor is quite precise after you've programmed it for your specific batteries. The reason I posted it is that a previous poster mentioned taking his batteries to 12 volts which it too low for long battery life.
Stu
Full cycling - what is that exactly? And a good battery should last a lot longer than 5 years - more like 8-10 if not taken below 50% of charge.

Hello Mitiempo

I don't know for which Trojan battery you posted the figures. I picked another at random from their website (RE series actually) and for that one, 12.2V is just over 60% SOC and 50% SOC is at 12.06 V. In the context of the measurements you're trying to make here I think that's a substantial difference. This is of course open circuit voltage so invalid under load or charge where you must compensate for voltage drop over internal resistance, also surface charge/diffusion effects at other than very low rates (hence the need to rest off load before measuring o.c.v.).

The actual relationship (as you can confirm from one of Trojan's more detailed tables) is that o.c. voltage per cell = (specific gravity + 0.845). (This will be at 25 deg C). You are not in any direct way measuring the state of charge of the battery; you are measuring the degree of conversion of its electrolyte. That's why the fully charged s.g. and the volume of acid have a significant effect. Have infinite acid and the o.c.v won't change as long as any charge remains, i.e. as long as there is any unconverted lead peroxide in the pos plates and lead in the negs. Some batteries (particularly maintenance free car or "leisure" batteries) have lots of spare acid with the result that the voltage drops less, others only just enough. Recombinant AGM batteries in particular have very little and usually a higher initial s.g. (we used 1.300 in the range I was involved in developing in the 1980s which were the first 10 year life ones and on which BS6290 pt 4 was largely based.)

I accept that a relationship established for a particular battery will be pretty good when the battery is in good condition but as soon as it starts to age a bit the accuracy will go off (just as will hydrometer readings).

What does "full cycling" mean is a good question. It's all a matter of definition. In Trojan's cycle life figures, do you know what cycle they are based on? I couldn't find it on their website. They certainly look heavyweight (there ain't no substitute for lead for good life!). Are they particularly expensive?

 

[mitiempo]

halcyon
Why is battery monitoring a grey area? You ask "what is a full battery?". The monitor knows this after proper setup. You don't just plug in a monitor. If you do you'll never get good results. When setting up a monitor (at least a Xantrex) you have to enter amp/hrs of battery and Puekert factor. Charged voltage for your particular battery is determined. CEF is also entered if the factory settings are not accurate for your system. It is synchronized when it determines the battery is fully charged and this is changed as a battery ages. So it is tailored to your batteries. It understands how many amps have to go back in for every amp removed (CEF), knows from setup when the battery is full and can give very accurate readings.
You suggest one should buy the cheapest battery to meet your needs. I guess if you use your boat seldom and don't rely on long battery life that would work, but a quality battery will last longer. On ther other hand if you're not concerned about state of charge and constantly drain the batteries excessively you might as well buy a cheap battery as their life will be shortened regardless.
Willow
I know state of charge will have a different specific gravity for different batteries. The reason I posted that is to show the narrow range between charged and dead. All the more important to know what state of charge your batteries are at any time. And a voltmeter can't tell you this in real life.
I understand the cycling in Trojan's charts is 50%, but the purpose of the chart is to show a comparison of their models and that would hold regardless.

 

[Heckler]

The life of a battery will depend, among other things, on the number of cycles it is put through and the depth to which it is discharged. Some battery manufacturers even quote typical life expectancies in terms of number of cycles for the various batteries they offer based on those two parameters.
Batteries intended purely for engine starting will not tolerate a huge number of cycles down to 50%, leisure batteries will tolerate more. True deepcycle battereis will tolerate a considerable number of cycles and can be discharged routinely to below 50%.

Delayed recharging of a partially discharged battery is another factor that will reduce its life expectancy.

Ah but I report on what goes on in real life, its all very well doing tooth sucking, I learned a long time ago that it is the bottom line that counts. My batteries were cycled deeply, many times and were still going strong after 5 years. They were bog std leisure batteries, bought from the local marine engine repairer.
Stu

 

[mitiempo]

In North America we have start type batterie and deep cycle batteries in flooded, gel, and agm types. There are also 2 volt traction batteries if you have the space and $. What is a "leisure battery"? No manufacturer I know makes one with that label.

 

[vyv_cox]

In North America we have start type batterie and deep cycle batteries in flooded, gel, and agm types. There are also 2 volt traction batteries if you have the space and $. What is a "leisure battery"? No manufacturer I know makes one with that label.

A leisure battery is a relatively low-cost deep cycle wet battery. It has fewer, heavier plates than an automotive starter battery and a void beneath the plates to accommodate debris that falls off the plates without shorting the cell out. Widely used in caravans, boats etc for domestic services where there is no continuous charging.

 

[mitiempo]

So it's a deep cycle, but not quite so deep?

 

[Plevier]

In North America we have start type batterie and deep cycle batteries in flooded, gel, and agm types. There are also 2 volt traction batteries if you have the space and $. What is a "leisure battery"? No manufacturer I know makes one with that label.

In Europe car start batteries up to maybe 80Ah usually have plates 1 - 2mm thick. Truck batteries tend to have plates 2.5, 3, maybe even 4mm thick. Plate separation is normally thin microporous PVC for low resistance and high current output.

"Leisure" battery is not a specific term but they would tend to use plates from the truck range and have multiple separation - often including a glass mat - to reduce risk of internal shorts from loose material or dendritic growth on the plates that occur more in batteries that are cycled and not kept at full charge. Sometimes an envelope separator enclosing the plate to catch shedded material is used. The thicker separation reduces the high current capability.

Purpose designed deep cycle flat plate batteries may have plates anything up to about 6mm thick. You get what you pay for!

 

[mitiempo]

Willow
Agreed.

 

[Plevier]

It understands how many amps have to go back in for every amp removed (CEF), knows from setup when the battery is full and can give very accurate readings.

CEF will vary with state of charge and rate of charge, that's a lot for a monitor to cope with particularly if use patterns are not consistent.


Willow
I know state of charge will have a different specific gravity for different batteries. The reason I posted that is to show the narrow range between charged and dead.

Agreed; and variations between models of battery will be significant compared with this range, that's why I said you can't assume the figures you gave are transferable.

All the more important to know what state of charge your batteries are at any time. And a voltmeter can't tell you this in real life.

Agreed!

I understand the cycling in Trojan's charts is 50%, but the purpose of the chart is to show a comparison of their models and that would hold regardless.

Agreed. I was interested to know what spec they use. I guess that's 50% of 20hr rating, and how do they define end of life - 80% capacity? I certainly wouldn't back any "Leisure" battery to achieve that. No doubt the Trojans cost a lot more though.

(see above)

 

[Allan]

FYI I have been quoted £250 for two Trojan 225Ahr batteries and, from another place, £120 for two 110Ahr "standard leisure" batteries.
Allan

 

[mitiempo]

Willow and Allan
Trojan T105 is priced at about $169 CDN, but I guess that won't make much difference to you. But here, maybe a 20-30% increase over the cheap ones.

Willow
CEF will vary but is consistent with a given battery. Here's the pages on setup from the manual. I think that while not perfect, they're very close, and no other method is anywhere near as close for finding out battery soc in a real time way. So much nicer to push a button instead of pulling out a hydrometer (after resting the battery of course).

 

[Allan]

Willow and Allan
Trojan T105 is priced at about $169 CDN, but I guess that won't make much difference to you. But here, maybe a 20-30% increase over the cheap ones.QUOTE]
Over here, as usual, they are a little more expensive (approx 25%). They are around twice the price of standard leisure.
Allan