Misread Trojan Battery Manual

landyacht318 wrote:
Well there have been many a general rule recommendation here that 1 Solar watt per 1 A/h of capacity and that is only about a 5% rate. This PDF trojan is recommending twice that.

1 W per 1 AH of bank is hardly a rule, it's better to exceed it, as long as the bulk current is within safe limits for a given battery.

But Trojan PDF is talking about a different thing. It says "amps of solar panel", not "amp-hours". So 210 AH bank should get 21-42 amps charging current. We discussed this before, and suggestion was made that this is a "minimum" recommended bulk current. In absence of other info from Trojan I tend to think that this is some "optimal" current, not a minimum or maximum. You can charge it at much lower rate, if you can then run a genny and bring it to 90% in a couple of hours.(Though it's better to run a genny before, and then run low-current solar).

For those who rely on solar as their only source, these 10-20% is pretty much a "recommended minimum current". To think of it, at 30A it would take +3 hours to bring SOC of 210 AH bank from 50% to 90%, and then it would barely get to 100% by the evening after few hours of floating.

I believe there exist a "maximum" charging current, at least for some AGM. For wets - I don't know. Mex says "it won't die", and I believe Mex :)...

MEXICOWANDERER wrote:
The C10 and C20 BCI rate was established for battery backup systems not generator power. When I lectured about this, battery engineers used to reply "Well that's our general doctrine". I asked them if they camp, drove 40 miles to go get gasoline, and put up with generator problems and wear-out.

"What's That Got To Do With It?"

There are probably ten thousand motorhomes out there that have good charging leads to the house batteries. Start the engine and the alternator tries it's best to put 14.4 volts into the batteries. Some of the newer Fords have 220 ampere alternators. The batteries won't die of seeing a higher than C20 rate. They'll die because of over discharge or sulfation.

Many have a fixation with C10 or C20 charge rates. WHEN YOU HAVE A SURPLUS of kWh charging available MOST OF THE TIME, then the percentage rates become valid. Until that point of recharge potential is reached, C10 and C20 is useless. Unless of course you just love to hear the nature-loving purr of a generator. I do not want to fatten the wallets of crude oil speculators and refiners any more than I have to. I have done number crunching (this means intensive, comprehensive analysis) of how much money batteries cost. Dollars per ultimate kWh delivered, total lifespan. People who run a generator at a C10 or C20 rate are kidding themselves. Fine, that's them - but it's another ballgame when they try to convince others that the C10-C20 theory is Holy Writ.

I subscribe to the FIVE PERCENT charge rate when utility power is available. Who cares? Time is not an issue. 24 hours at 5 amps is enough to fully recharge a pair of group 24 batteries.

Reminds me of someone who spends a hundred dollars on D cells, for reading to save two dollars on the electric bill.

yup, I agree

lower charge rates (C/10, C/20 (5%)) etc. usually will give longer cycle life (number of charge discharge cycles) than high charge rates. So, it somewhat depends on what is more important, high cycle life or short charge time. For Trojan 6V, the cycle life is high enough that most RV'rs, will never have cycle life determining battery life, age, sulfation etc. will hit first. Personally when I'm dry camping and using the generator, I hit the batteries with close to C/2 or C/3 charge rate. yes, I'm probably loosing some cycles, but not enough to worry about. Under solar, the charge rate is closer to C/30. My last set of batteries were 10 years old when they went to in-laws and 3 years later are still working fine with SG still up there. Lost some capacity but still highly useful.

Now if I lived off grid year round with solar for charging, I'd size my system for around C/20 for long cycle life.

Decide what's important, and pick your tradeoff. No free lunch.

The C10 and C20 BCI rate was established for battery backup systems not generator power. When I lectured about this, battery engineers used to reply "Well that's our general doctrine". I asked them if they camp, drove 40 miles to go get gasoline, and put up with generator problems and wear-out.

"What's That Got To Do With It?"

There are probably ten thousand motorhomes out there that have good charging leads to the house batteries. Start the engine and the alternator tries it's best to put 14.4 volts into the batteries. Some of the newer Fords have 220 ampere alternators. The batteries won't die of seeing a higher than C20 rate. They'll die because of over discharge or sulfation.

Many have a fixation with C10 or C20 charge rates. WHEN YOU HAVE A SURPLUS of kWh charging available MOST OF THE TIME, then the percentage rates become valid. Until that point of recharge potential is reached, C10 and C20 is useless. Unless of course you just love to hear the nature-loving purr of a generator. I do not want to fatten the wallets of crude oil speculators and refiners any more than I have to. I have done number crunching (this means intensive, comprehensive analysis) of how much money batteries cost. Dollars per ultimate kWh delivered, total lifespan. People who run a generator at a C10 or C20 rate are kidding themselves. Fine, that's them - but it's another ballgame when they try to convince others that the C10-C20 theory is Holy Writ.

I subscribe to the FIVE PERCENT charge rate when utility power is available. Who cares? Time is not an issue. 24 hours at 5 amps is enough to fully recharge a pair of group 24 batteries.

Reminds me of someone who spends a hundred dollars on D cells, for reading to save two dollars on the electric bill.

Well if Trojan is recommending a 10 to 20% rate when charging regarding solar, one might assume they are thinking a stationary off grid situation and that solar is the primary if not sole recharging source.

A discharged battery can certainly accept way more than 20%. I've seen my flooded 31 rated at 130 amp hours take 65amps from my alternator which is 50%. My paired 27's could easily suck up 90+ amps when my alternator belt would start squealing.

I did not take SG readings often on my previous pairs of group 27 batteries rated at 230 amp hours fed by 198 watts of solar, I wish I did.

But now I have the same wattage feeding only 130 amp hours of battery and the same general overnight usage. With some tweaking to my solar voltage setpoints, I expect to get a respectable lifespan from my battery in my usage, and a better return on investment than my previous sets of batteries which had larger capacity and were cycled shallower, daily.

Is this due to the voltage setpoints being tweaked in response to SG readings, or due to the Solar coming closer to a 10% rate, or some combination of both? I know not. I have my suspicions and of course I want those to be right.

We all use and recharge our batteries differently. I cycle mine 30 to 50% each and every night and my solar makes up for 90% of the overall supplied recharging current, and I feel that lowering my capacity to approach this 10% Solar recommendation will have me spending less money on replacement batteries in the long run. I have no generator, and rarely plug in. Time will tell.

BUt in the OP's linkm a well respected battery manufacturer is recommending a 10 to 20% via solar, and an oft touted spec on this and other forums is just ~5%. or 1 watt per 1 amp hour of storage.

The 5% figure is certainly easier and more practical to meet. I certainly wanted to believe when Mine could barely reach 5% that it was enough, but I never really got more than 2 years from a pair of batteries cycled daily. Now I've got closer to 10% by having lowered my capacity, and want to believe this will be better in my uses, and cost less in the long run, and it does still have enough capacity to meet my needs.

Everything is a compromise. Data that backs one's choice of compromise gives the warm and fuzzies. Perhaps warm and fuzzies are worthless.

Time will tell.

Regarding float voltages, I consider in my use, float voltage to be 'Storage' voltage. I'll lower it to 13.1 if/when I stop cycling my batteries daily. I set my float voltage as a 'finish' voltage and above my Absorption voltage and only by this method does my SG approach baseline daily.

I think I am confused here. Is a c20 charge rate at 5% amp hour or 20% of the total ahrs a battery has?

MEXICOWANDERER wrote:
Keep in mind...

A battery manufacturer is going to insist on care and maintenance that makes the battery and them look "the best".

Charging time requirements, worn-out generators and long drives for gasoline are no object - optimum battery life is number one. Even if 10% added battery life costs 40% of the original cost of the battery.

Back float voltages down to the point where a fully charged battery does not lose or degrade the density of the OEM specific gravity of a fully charged new battery. This is trial and error. No 24 pin logic chip on the face of the earth can replicate this protocol.

Once a year watering? Mena, try not to imagine nits to pick too hard. Engineers have to say -something- or they eventually get a pink slip. "Hey there Roy, tell us why we are paying you 80K a year?"

Battery manufacturer's "instructions" should be regarded as tips and hints. Not gospel!

Armed with a voltmeter and a hydrometer an informed consumer can rip the shorts off any battery engineer whose guesses are far removed from the site of the battery itself. I wouldn't argue with BFL13, or Mena, for instance for all the tea in China. What they find is reality. It's foolish to try and outguess facts.

Thank you for weighing in MEX! Since I have this adjustable power supply now, I'll play with the voltages to see what happens to SG. I know 13.6V works. I have it at 13.2V now. Once the acid gets mixed up, I'll play around and see what's best for fun. But if 13.2V works for a summer voltage, I'll just leave it at that.

NinerBikes wrote:

landyacht318 wrote:
I've not seen this particular Link before.
I like the "tips on how to maximize your battery life" at the bottom:

As a general rule of thumb, the total amps from your PV panels should be sized between 10% and 20% of the total amp-hours (Ah) of the battery pack.

I deliberately lowered my battery capacity so that my solar can just barely reach 10%.
198 watts for a 130 A/h battery

I've taken some minor grief here and there on this forum for employing this strategy.

So a 210 amp 6v pair of GC-2's should get between 21 and 42 amp/hours capacity from the solar panels, for the day, if I am reading that correctly? I get 6.5 to 7 amps/hour at as close to 15.0V as I can for a Trojan T -1275... and 50% of a 150 amp hr battery is 75 amps to be replaced max, per day. No way I am going to get that kind of output come short days of winter and the sun low on the horizon. Summer time, yes.

I think many are misinterpreting this. I am pretty sure what is meant is to charge at the C10 or C20 the AH rate, ie for a 210 AH battery the MAX charging rate should be 21 Amps (C10) or 42 Amps (C20) That is the charging current in AMPS, not total AMP HOURS. When the batteries are low they will accept for example a max of 42 amps which will reduce as the batteries approach full charge.

On a somewhat related note, my BlueSky solar controller will supply a max of 25 Amps. BUT at that current there is a full volt drop between the controller and the battery because of the long #6 leads so although the battery had only reached 13.8 volts the controller thought they had reached 14.8V and began to reduce the charge voltage. To try overcome this I increased the controller output voltage but this of course allowed the battery voltage to go too high when the current (and thus voltage drop loss) decreased.

The point of this last: Ensure that the solar controller is very close to the batteries or at least use a controller with remote battery voltage sense.

Keep in mind...

A battery manufacturer is going to insist on care and maintenance that makes the battery and them look "the best".

Charging time requirements, worn-out generators and long drives for gasoline are no object - optimum battery life is number one. Even if 10% added battery life costs 40% of the original cost of the battery.

Back float voltages down to the point where a fully charged battery does not lose or degrade the density of the OEM specific gravity of a fully charged new battery. This is trial and error. No 24 pin logic chip on the face of the earth can replicate this protocol.

Once a year watering? Mena, try not to imagine nits to pick too hard. Engineers have to say -something- or they eventually get a pink slip. "Hey there Roy, tell us why we are paying you 80K a year?"

Battery manufacturer's "instructions" should be regarded as tips and hints. Not gospel!

Armed with a voltmeter and a hydrometer an informed consumer can rip the shorts off any battery engineer whose guesses are far removed from the site of the battery itself. I wouldn't argue with BFL13, or Mena, for instance for all the tea in China. What they find is reality. It's foolish to try and outguess facts.

40 to 50 amp hours out of a 150 amp hour battery is 66 to 70% SOC. Portable, aimable panels up your amperage take over more hours per day. Another observation is that when I run 15.0V out of my charge controller to that T -1275, the charge controller seems to stay in bulk mode and at higher overall amps going in to the battery, in pulse charge mode.

I mention this because one of the charge controllers I have, while adjustable for voltage, really drops off on the amps it provides 66-75% of the time, with it's pulse charging algorithm. The solar 30 Amp charge controller I bought, for $33 off of Ebay, is much, much better in terms of keeping the amps up and pushing from my 120 watt portable solar panel, capable of 6.6 to 7 amp hours... 6.5. 6.33 6.28 6.5.... The 10 amp unit I bought drops off to 3 or 4 amps. Easy to measure when you put a little $15 RC battery charger meter in line and take a look at the output. Not all solar charge controllers are worthy. This is important on cloudy days and when counting on your solar panels to keep you off the generator as much as possible.

I think part of it depends on how deep your cycle is. I have four GC2s because I run some high draw items for relatively short bursts, but my usual cycle is only to about 75% rather than 50%. The approximate 5% solar does well with that, but I would need much more if I were trying to bring back 50% every day.