Newbie battery questions

[madlabs]

I'm soon to be moving off-grid. It's an econmy based move, I can't afford the mortgage and the rental. So, I got a 40' container delivered and I'm moving a 35' trailer out there next week.

Anyway, I just wanted to do a sanity check on the following basic system.

I have a 5kW gas generator that will be used to charge the batteries. I am purchasing 6-8 T105 batteries for 660-880aH. I read that charging at 10% of the bank capacity is the way to go. So I can charge at 60-80 amps, depending on the bank size.

Of course, since I am charging from a generator, I want the shortest charge time I can get, while taking care of the batteries. Assuming I stick to using about 20% of the batteries capacity, I will need to charge around 120 to 160 aH each day. That should take about about 3.7 hours per day with a 60 amp charger. Does that seem about right in reality? I calculated that simply by 120/6*1.4. Is that a reasonable way to figger it?

So, I need a charger. Am I better off getting 2*40 amp chargers, or getting 1 larger charger? Anyone have any reccomends for brand/model of charger? I need a simple, cheap, dumb charger, due to costs. While I know that I am too poor to buy cheap, I am serioulsy finacially restricted. If I can get a couple of years out of the system I will be happy.

I can see that undercharging is going to be my biggest problem, leading to sulfation and early battery death. I have built a pulse desulfator and am playing with that. Can I use the desulfator to compensate for lack of equilization charges?

Thanks for the help!

[bob g]

using the top 10 or 20 percent of the battery capacity will greatly increase

the life of the batteries, but

it will be more than offset by the amount of fuel required to charge them.

far better off to use them down to 50 percent, charge back up to ~80-85%

and repeat the cycle for a week to 10 days, then on about the 10th day fully charge them as needed, which will require several hours run time.

the 50/80 regime is the most economical regime for a flood lead acid battery

you can step up to a higher charge rate of approx 20-25% of capacity

or around 200 amps. this allows you to get the charge cycle done in about 2 hours per day as opposed to going the top 10 or 20 every day which will likely take over 4 hours to finish.

hope that makes sense?

check Balmar, Ample power and just about any marine site and study up on this charge regime. it is the most cost effective all things considered if you have to charge with an engine driven generator.

you might also consider losing one layer of conversion, that being a gas driven gen

providing power for a charger to charge batteries

if you must use an engine, use a high capacity large frame alternator, and a balmar

mc612 or mc624 or equivalent. that will provide 3 step charge control, the ability to tailor the alternator to the available hp of the engine driving it, soft start and a bunch of other stuff.

no sense doing any more conversions than necessary in my opinion.

bob g

[dnix71]

Is it okay to ask what you plan to use the batteries for? If everything is 12 volts, then you should be fine. You can leave the pulse desulfator plugged in all the time if it's a small one like my Sulfarid. It will shut down when the battery voltage gets too low and restart when you turn the generator on.

You are going to go through a lot of fuel recharging batteries with a generator. How long do you plan to be offgrid? Solar panels on the roof of your trailer for daily recharging and using the genny once a week to equalize would be more economical in the long run.

[scottsAI]

Madlabs,

Bob g's advice is on the mark.

The 80/50 cycle is good, don't freak out if you discharge occasionally goes below 50%.

Deep cycle batteries are made to be discharged, 70% for a short time should not hurt anything. Now discharges near 80% or below will damage the battery and is a good time to freak out!

Lead acid battery charging efficiency is 91% when SOC is below 80%, above 80% SOC the charge efficiency begins to drop off linearly to zero at 100% SOC. The 80/50 makes good use of the efficiency of the battery for day to day operations, a full charge 90-95% SOC should be done along the lines of Bob's recommendation. Two to four times a year an equalizing charge should be done, 100% SOC. Not good to do more than 6 equalizing charges a year. Of course follow manufactures recommendations.

Sulfation is about the time spent discharged and depth of discharge.

Better to charge ASAP after battery discharged.

Therefore charge at end of day, let it sit overnight charged!

Goal, set up the charge / discharge to achieve the minimum time discharged.

Have fun,

Scott.

[madlabs]

Gentlemen,

Thanks! This is just the kind of practical advice I was hoping for! I'll use the charge regime y'all describe.

Dinx, the batts will be used for both 12V loads and to run inverters. Is it ok to have an inverter and a desulfator runnning on/off the batts at the same time? I'm going to be off-grid for the rest of my life if all goes well. I am going to start adding PV's as finances allow, but ATM all I have are 2*60 watt panels. On the plus side, I have as much sun at the spot as you can get in my zone (coastal, fog).

I'm going to look into converting an old genny I have to run an alternator as you suggest. I think my bro in law has one with a dead genset but good motor. If not, I have a decent honda lawnmower I might rip the engine from. I have an old truck with a

pretty fat alternator if IRC.

Thanks again! This is just the kind of practical advice I need!

[zeusmorg]

 You may also consider running your genny at your peak usage time,If you have a total 12v system set up, then using the electricity while you're generating it will be most efficient, you bypass the storage losses that way. If you're using a 120 v. alternator, and converting to 12 v for storage and then back to 120 v for use, your efficiency losses add up in every step, so using while generating would give you even more efficiency!

 Just some thoughts, running your entire system off gas is probably the most expensive way to generate electricity there is. Diesel would be a bit more efficient, propane a bit more so. Also the least amount of conversions lessens the losses in each step.

 I'm sure you've thought of a lot of ways to conserve power and energy use. Wood for heat, for example, solar for heating water. Doing a totally new setup in a new environment takes a LOT of work, so try to keep each thing as efficient as possible, that way you'll be less likely to have to change a system in the future.

 There's a lot of tradeoffs, for instance 48 v. is the most efficient when it comes to DC (and still remain out of code, and stay safe) You'll find it's better to get up with the sun, rather than sit up late at night burning up electricity reading (or whatever) Just think of how your great great grandparents would've done things, before electricity was around! The charging suggestions are very valid given here. You want your basic charge somewhere around 10%. Never over 20%, which can lead to overheating in the batteries. An equalization charge should be done AT LEAST once a year, better to do it every 6 months.. And take the best care of those batteries you can, distilled water ONLY! keep them properly topped off, never allow the water to drop below the tops of the plates.EVER!EVER! check that monthly. Get a good hygrometer to check state of charge of each cell. Record everything. That way you'll get a feel of how your batteries are doing.

[spinningmagnets]

Madlabs, whole sytems that are properly comprehensive are expensive, and I am very sympathetic to your need to start with a small cash-only system.

I have a dozen plans simmering on the back burner, and your plan is also my most basic plan. Container storage and an RV/trailer.

Early system components can be sold later, so they are not "lost money". In the beginning I most want lights at night, music, and a water pump. All of these are easily and cheaply achieved with 12V.

I desire a wind and solar PV element eventually, but as far as up-front costs, a back-up generator is vital for extending battery life (I'm told) on low-wind/low-sun weeks, a low battery can be deep-cycled. If left discharged at less than 50% for an extended time, which as others (with much more experience than me) have stated is very bad for the expensive battery packs life.

To this end, my most basic plan starts with an inverter, a small battery pack and a generator (with mostly 12V direct-connect components). Wind and sun will be added later. My most desireable generator is a diesel, because they can be adapted to run off of waste vegetable oil (WVO) which is old cooking oil from restaurants.

That being said, the absolute cheapest generator (as you know) is the lawnmower-engine/truck-alternator. Here's a helpful link:

http://www.qsl.net/ns8o/Induction_Generator.html

A useful thing to know when you are on a very tight budget, you can weld bed-frame angle-steel with 2 or three car batteries. 24V for thinner stuff, and 36V for thicker stuff. I adapted an old cordless 12V drill to a lamp cord and clamps to use a car battery (stock battery died after 3 years, wife got me a new 18V). Drill, hacksaw, welding, and you've got a good start.

I might also suggest putting two 55-gallon drums on the roof of the storage container to give you gravity-feed water, One cold, one hot (top off water when generator is running, instead of using battery). If you route the exhaust from whatever generator you are using through a "U" pipe that dips into the hot drum, the water should be at least warm.

Best of luck

[madlabs]

Once again, many thanks for all the lengthy and thoughtfull replies. This forum is a motherload of great practical info.

I have no choice but to use the gas 5kW genny for starters. Economy. That link for making a genny from a lawnmower engine is great! He shows using motors to get 120VAC, but I'll go with an automotive alternator. Is it best to use one with an external VREG? I can see easily making an electronic VREG to substitute for the old school mechanical style.

Luckily for me I live in a little cabin in the woods now, with an outhouse and poor power, so the shift won't be to radical a change. I converted my hot tub to solar/wood heat last year, so I have some panels and practical water heating experience. I have a few tanks too. I LOVE the idea of routing the genny exhaust through a water heater tank. That should be pretty easy to do.

I must say that in a way I'm glad I'm being forced to move out there, instead of waiting for the day I can "afford" it. Nothing like groveling in a trailer using candles to light a fire under yer butt!

[spinningmagnets]

If you use "Google search the board" and look for leece neville, they are fat 140+ amp 12V alternators. Apparently they are used on 18-wheelers and similar equipment. Everything on my 18-wheeler is 12V, except the starter has a 24V circuit to keep the starter motor reasonably small.

When they have a problem with a diode or bearing, they are often thrown away for scrap price and a new unit installed, rather than rebuilt (so I'm told). If this is true, you should be able to get a couple very cheap from any major city.

There's so much helpful information in the posting files, as you scroll back through the last few years, copy/paste useful story links with a one-line description. I have about 11 pages worth.

Here's some fun and helpful links:

http://www.backwoodshome.com/

http://www.motherearthnews.com/

http://www.builditsolar.com

[bob g]

on north american trucks the total system is 12 volts in 99% of cases

not sure about european trucks maybe they are 12/24 or straight 24 volt systems

the leece neville/prestolite 110-555jho alternator is a large frame 160amp unit

12 volt nominal, it uses a piggy back regulator that is easy to remove and fit a

proper 3 stage controller such as the balmar, xantrex, amplepower, hart, etc

and there are at least 2 other controllers made in england that i am aware of

that do the same job.

the 110-555jho uses large ball brgs front and rear, has brushes that are user accessable without removal of the alternator or a complete teardown, the unit is rated at 160 amps at 70 degree's but figure on ~120 continuous output hot.

they use a standard 7/8" bore pulley so you can get any size pulley you want to fit

them easy enough.

they are about 54% efficient at charging 12volts nominal, which is about as good as any alternator, but

should you decide to go with a 24 volt bank, i can get you well into the low to mid

70's efficiency with a bit of modification. i have a prototype system that is doing quite well at very good efficiency generally not seen with automotive alternators.

the beauty of an belt driven engine/alternator setup is you can dial back the rpm

when you are topping off the battery and reduce noise and fuel consumption as well as increase the longevity of the engine in most cases.

also with a bit of work, one can fab up and fit a heat exchanger to the exhaust and make domestic hot water as well, which is a very good use of waste heat that would normally go up the stack anyway,, everyone needs domestic hot water for laundry, washing dishes and a hot shower is something that is nice as well.

the last thing i would want or recommend would be a 3600rpm AC genset, screaming for hours to provide power for a charger, to charge batteries so that you can then

power inverters to power loads later. too many conversion steps and your efficiency will be dreadful even with the best of equipment.

eliminating conversion steps enable you to use less costly equipment and still get better efficiency overall.

don't get sold on "single" point efficiency, such as "our charger is 98% efficient"

(which it likely only is 98% efficient on a cold day, at a specific load, at sea level, at a specific baro pressure, if you hold your mouth right.. etc, and be well off that level of efficiency in the real world anyway)

what you should focus on is "total" system efficiency, learn what it takes to improve the total efficiency. small things sometimes can make significant improvements in total system efficiencies.

it is the total system that consumes the fuel to produce kwatts that you will consume.

and remember each watt conserved is worth a lot more than each watt generated

as ben franklin said, "a penny saved is a penny earned" in this game it likely

is "a watt conserved is worth 3 watts generated" maybe more, but likly not much less.

as for desulfators, forget them!

you got new batteries, so use them properly, charge them properly, and it is unlikely that you will ever have a need for a desulfator. There is ample evidence that they will not improve the lifespan of new batteries and some evidence that they might even be detrimental.

if you are set on useing one, use it only during your equalization charging, the rest of the time just do the standard 3 step charging, keep a log, and learn to use your temp compensated hydrometer.

good luck

bob g

[Bruce S]

Another place to "find" a good genset with respect to 18 wheelers is the APUs on the seat cover side of the rigs ( that's the passenger side) those litle APUs can be found sometimes a lot less that a good sized solar set and one unit that I am helping with is working great with WVO thinned with 10% keroseen.

If you get one, a quick way to make it much more use full is to use fresh coolant and use it for waste heat recovery for heating water.

The units sip fuel when in idle mode and are 3cyl units.

New the units normally start at 6Gs and go up from there. Used are had even around here less than half.

Best of luck with your off-grid move, sounds exciting.

Bruce S

[spinningmagnets]

Great idea, Bruce! I have recently read that there is an increasing use of APU's, as letting the main engine idle (one gallon of fuel an hour?) for the air conditioning or cabin heat is being restricted in various juristictions.

I also recently read about how the 18-wheeled trucks that have a refrigerated trailer (reefers) have a diesel fuel powered freezer unit on the top/front of the trailer.

I'm sure there are many brands and models, but a quick Google showed there are small Yanmar (China) and Kubota (Japan) diesels that are popular. If truck shop cores could be found cheap enough, perhaps two bad ones could be made into one "useful" one. I am a fan of WVO fuel.

[Bruce S]

Madlabs: Hope you don't mind the diversion of original post

spinningmagnets:

Best I know ALL the newer truck have to have these. States are coming down hard on ones that do not. These are awesome units. They have all the controls in the "entertainment" section right along with being able to control the HVAC from a cool little touch pad.

The reefers on the top are nice and would love to have one that's diesel powered, but those bad boys aren't cheap even used.

Their is also a burner section that I'm looking for that was originally a heater section for sleep overs. I've seen them fired up and the waste heat alone will heat a 55gal drum is short order. They've fallen out of favor and so are even harder to find.

WVO is nice to work with. I've finding the more I have the more "things" I can do with it. Fuel and soap, who knew :0.

Cheers ALL;

Bruce S

 

[madlabs]

Thanks again for all the info. I don't mind the hijack of the thread at all, I'm learning a lot.

I have procured a 5.5hp Honda lawnmower engine and have ordered a bracket to mount it and an alternator from a place called Epicenter. I'm going to start with a regular alternator and use it for bulk charging. I'll add a smarter regulator as finances permit.

What fun! I just love tinkering with stuff like this. I have an old Makita genset (dead) that I am going to highjack the frame and fuel tank from to mount the rig on.

[ghurd]

I expect you saw something about this earlier...

But it can be a good idea to limit the charging amps somehow.

CaveMan style is to use undersized wire between the battery and alternator.  It can get hot.

Slightly more advanced than caveman style is a low voltage, high wattage bulb in serises, then remove it from the circuit a few minutes later.  That's the general idea.

Nothing scientific in all that, except expect it to stall until the kinks are worked out.  

Stalling on the first configuration or 2 would be normal in my opinion.

G-

[madlabs]

Yup, I'm aware of the overcurrent issue. I found an alternator with an external regulator, so I can make a smarter replacement. Unfortunatly it is a 63 amp alternator, so I best not pull more than 50 amps or so from it. I have a beefy 25 ohm pot that I can use for starters to limit the current. I saw a simple regualtor citcuit which I will probably build first, then make an MCU controlled version as time permits.

Just cleared the spot for the outhouse. Digging the hole tomorrow. Progress!