Dc motor/generator

[slowspeed1953]

Ok guys got a question.

Say I have a 48volt battery bank that I want to charge at 150amps, my dc motor/genny is rated at 100 volts and 200amps how would I produce a c20 (150a) rate charge on a 750a 48v bank?

Doesnt the battery bank serve as a voltage limit IE. 48volts max genny output until the battery bank reaches capacity?

Is there a formula or would I have to play with genny speed until I got the amperage output I desired?

Best wishes

[GuyFawkes]

If you apply excess voltage in reverse polarity to a DC battery a charging current flows

Internal resistance of a DC lead acid battery is very very low, your dynamo will produce 100 volts or 200 amps, not both.

what you want to aim for is 60 VDC more or less...

a C20 rate of charge is putting 2000 Amperes into a 100 Ah battery, so you don't want that, even if you could do it.


going back in time a bit when large DC accumulator banks charged by Dc dynamos was common, *nobody* just threw a frankenstien lab type switch and coupled a spinning dynamo to a accumulator bank, dynamo field strength was controlled by a regulator, I suggest that is the solution you need, especially if you want efficiency as well as practicality and safety.

[mobile_bob]

batteries are expensive and deserve to be treated correctly,
"usually they don't die of old age they are murdered "

direct coupling to a generator, without some decent form of regulation, either electo/mechanical or
you monitoring state of charge, gassing, battery temp and correlating all the above based on ambient temp. is setting your
batteries up for an untimely death

far better approach would be a dedicated alternator, controlled by a programable regulator with temp compensation.
these things set the maximum charge rate based on all the variables and will give you the best of all worlds. or...  generate
ac and plug in a quality stepped charger to do the job (with a drop in overall system efficiency)

bob g

[Doug]

That true Bob, and so is the right choice of battery. Iwouldn't expect a deap cycle marine RV battery to last long in an off grid home aplication. You need to look at realy good set of batteries from a fork lift  or other industrial aplication.
I just watched the scrap man take 271 loco to the recycler a few weeks ago 4 tons of premium lead acid in that battery pack ( I should have asked for it but the wife would have freaked ). Those batteries had a hard life, stupid miners never charging them properly, lazy electricians not watering its batteries often enough. Still it could hold a charge for about 8 hours heavy use hauling trucks from the station to the load out and back. A realy good battery will take a lot of chagr cycles where a cheap one will not.
Oh ya some stupid miner killed my beloved 1940s electric train ( I love trains, the proper kind with batteries not diesel ).

Doug

[mobile_bob]

i am leaning toward the rolls/surrette 5000 series myself
10 year warranty, expected lifespan of 15 plus years,,, not bad

i ran the numbers a few years ago, dollar for dollar, amp/hr to amp/hr, when factoring discharge cycles it is
amazing how close all deep cycle batteries are in cost per amp/hr over their expected lifespan.

i am with you on the scrapped one,, i would have though hard and long about grabbin it too!
if it would drag the load around for 8 hours it would probably work for a very long time for what i have in mind.
most of that sort of battery around here is used up, by the time it is ready to be traded in.

our primary truck battery supplier also does vrla batteries for telecom companies, we can sort the take outs, and use them for free,,, not bad , but not my choice for an offgrid home.
bob g

[Doug]

The two 4 foot by 5 stacks in the Kiruna are worth about 200 grand, last about 2 years. Saft NiCad flooded wet cell each is rated at 90 ah per 1.4 cell. They're aircraft batteries, I'm sure they are about as good as it comes and I'm hoping th Kiruna drops dead so I can salvage the stacks ( hopefuly in some horable crash that smashes into two pieces at the mid ship so batteries aren't harmed ). The flooded cell NiCad seem to be better than the lead in the long run too, but I here there is a new sinter plate lead process that will reduce weight per ah and give a longer service life. I hate batteries ( the part where I crawl on belly under the cab of a truck adding water the most ), but I'm optomistic there's still improvement coming that will make them a more cost effective means of energy storage.

Doug

[peterako]

you will need a charger max. 52 volt 150 amp or using a special expensive inverter 100 volt to 52 volt by 150 amp.

use only deep charge solar or industrial batterys ( car or truck will boil to death with in a year )
 i use a 24 volt setup on this way perfect.

looking by google is a great help.

[Andre Blanchard]

I want a set of these.
http://www.beutilityfree.com/batteryNiFe/battery_flyer.pdf
Main page.
http://www.beutilityfree.com/

But man the cost, a quote from their web site.
"For battery financing review the detail here!"


Doug:
You can get remote watering systems for systems that were not designed for proper, easy maintenance. 

[twombo]

Bob, as nice as the Rolls/Surrettes are, the HUP Solar One's look pretty competitive in terms of dollar per a/h and lifespan.  They also have very competitive warranty.  Free shipping too most many sellers.

Here is a link:

http://www.thesolar.biz/Cost_Table_batteries.htm

Batteries, batteries, i'm always thinking batteries. checking  watering, charging, equalizing... seems like my life's rhythym is kept time by batteries!

Need a good slow speed genny to change up a little, I guess.   

Oh yeah, thanks for the links for the Balmar regulator. Fairly reasonable priced, although the "Mark8" (http://www.homepower.com/files/mark8.pdf ) in Homepower magazine is an interesting homegrown possibility. 

The Balmar is programmable and proven reliable and I prefer one experimental technology at a time. I can put up with the maturation of a slow speed diesel with a proven electronics package, but not both at one time!! I just want reliable  and reasonably cost effective  backup power for my off grid home.

Regards

Mike

[OffGrid]

Mike

I made the regulator as shown in the Home Power artical a few years back. It works great and can be set to limit both voltage and current. Its on an 80 amp, 24 volt truck alternator which is just OK. Typical automotive alternators drop in output a fair amount when they get hot. The expensive Balmars types will put out at rated power all day long. So you may want to oversize if you go the automotive route which will be less expensive.

Cheers, Svend

[slowspeed1953]

Hey guys thanks for the replys!

Another question, I dont want to use a alternator as the eficiency is lower than with a permanent magnet generator so I think the balmer controller is out. I am really concerned about fuel consumption as 10% less efficiency is 10% more fuel. That really adds up in a daily use application.

Im not dead set on a 48v 750ah bank (although my 1st choice) I am also considering a 24v 1500ah bank.

That being said what are my options regarding generator selection and control?

Peace&Love , Darren

[mobile_bob]

Darren:

when you go to pm alternator you pick up unit efficiency but lose in overall system efficiency because of lack of charge rigime control

the only way you could get some control on output would be to vary the rpm, which the listers have an issue with, and the petters might as well

you might do a google on buck/boost alternators, it is a mix of the two technologies, in that they are pm alterators with powered fields to either buck or boost output
serious output and serious dollars,

also check out electodyne.com, they make a rather unusual and high efficiency/high output alternators, from 12 volt at 450 amps up to 64volt 100amp units. also pretty pricey, but excellent machines that are made to run forever.

bob g

[Doug]

I'm done boycotting.....

Yes Andre Blanchard your right there are watering systems designed for these batteries, but they don't work very well. I'd rather bitch and complain for having to climb on top to water than use words that would make a salor blush for having to crawl in there and get a few dozen pokes trying to change a cell that looks like a used road flare.

There is also an LED electrolite level sensor for the Saft air craft batteries, they work well and short out and set the stacks on fire even better ( Ore fines and wiring don't mix )

Lastly Bob's right about the PM alternators, but everyone who reads the Otherpower forum and latches on to ther concept has it in their heads this can be easily adapted to serve as an engine driven system.
The reality is you need field control.
You need to run at a frequency and flux density that doesn't cause you to heat the iron to excess ( unless of course it is your desire to heat the building your genset is sitting in by way of induction )
You need to match your load, your electric machine and prime mover to work together for max efficiency.

Doug
 

[mobile_bob]

amen Doug,

and then...

others:

you need to study the charging needs of the battery type you are going to use.

if you are going to use flooded cells, then i would suggest going to the marine sites and study what is the most efficient way of charging the batteries.

once you understand how to efficiently charge your batteries it becomes apparent that one has to design a system around those parameters, not the other way around!

first determine your loads,
second determine how long you want to go between charging
then calculate the bank size needed.
then factor in the most efficient way of charging them ( read again about marine charging)

then and only then can you design and build and efficient genset to do the job.

otherwise without this understanding you will run countless hours, tons of fuel, destroy batteries and be very disappointed.
unless...

you are very lucky, or learn from your mistakes and alter your lifestyle to fit the ill begotten design.

the following is an example of a theoretical system without regard to battery efficiency

say you determine you need 300 amp hours per day, and want to charge each day.
if you size your system based on this info and get a 300 amp hour set of batteries you will be running a generator, many hours to recharge them properly

if instead you sized the bank to 1000 amp/hrs, and draw them down to 50% then..
recharge them from 50 back up to 80% State of charge (effectively giving you the 300 amp hrs you need), you can do that in perhaps an hour or so, because flooded cells can absorb an enormous amount of power between these levels without gassing.
then once every week or 10 days bring them all the way back up to 100% which will take many hours then.

whole books have been written on this subject, i would suggest anyone thinking of going the battery route to study well.

otherwise you will spend alot of cash on a system that will die a horrible death, and while doing so run many hours needlessly and consume alot more fuel.

bob g

[mobile_bob]

further observations on the use of automotive alterators

one has to consider a couple of  points

1. these units are built on a price point objective, in other words, how cheap can we make em and still get the job done

2. they are made to operate over an extreme rpm range, effectively being a jack of all trades, master of none.

you have to find the sweet spot, or in effect the most efficient rpm of an alternator to get the most out for the least input in hp and fuel.

if you want 50amps output, it makes no sence to spin it at 8000 rpm to do so, when in reality the thing might put out nearly as much at a much lower rpm

for instance a leeceneville 110-555 will output 90 amps at ~1500rpm, it has a top speed of ~8000 rpm, to get 90 amps at 8000 rpm will take substantially more hp than if you run it at 1500rpm

this is why it is important to check out the output curves of any alternator, if you cannot get output curves pass on that alternator, unless you have alot of money and time to experiment with belt/pulley ratio's

the next consideration is the prime mover/engine, most have sweet spots as well where, noise, vibration, fuel consumtion etc are at agreeable levels, what that rpm is needs to be known

once having both rpm of the alternator and engine the ratio is easy to figure, then you have a set that runs smooth, as quiet as possible, and as economically as you can. next..

another issue is the voltage regulator used for automotive applications, it is poorly suited for offgrid deep cycle work. most folks already know this, but some may not. if you don't know this you will be disappointed in the operation of your genset.

while an automotive regulator will charge your batteries it will take a long run time to do so, marine charge controllers and their counterparts take sophisticated control over the alternator and the charging regime of the batteries, to pump in the maximum amps based on temp, battery type, state of charge and other factors.

hope this helps someone, to save some time and money and make for a useful outcome.

bob g