max battery recharge rate
T Bodin
I have a charger/battery/inverter system in a cabin in the woods that i
visit on weekends. There are 4 batteries, 6v each, wired into two banks for
a 12v system. These were the $45 variety golf cart batteries from Sam's I
bought 4 years ago. I have a Statpower 40a Truecharge charger and a
Statpower Portawattz 1750 inverter in the cabin. I also have a Honda 1400w
generator. The whole system works really slick and has continued to do so
for 4 years now of roughly 10 weekends per year.
I would like to change the situation for two reasons. I am willing to buy a
second generator if I can do so at a good price, so I can leave it at the
cabin and stop lugging the unit back and forth on weekends. I would leave
it there but my better half wants me to have the generator at home for the
2x per year when we have power outages in our neighborhood. The second
reason I would like to do this is because of the charging rate of the
system. After a day of lights and TV at the cabin, it takes about 5 or 6
hours of charging to get a good restore on the batteries. Part of what's
best about this place is the quiet (OK, I do have a TV), but I would rather
not run the generator that much.
I have been studying over the years the do it yourself 80-150a DC charger
ideas, and also have seen products like the 100a Genny Deecee, the new 75a
Coleman Ultimite, and another smaller capacity charger from a small 50a
outfit at http://wildernessenergy.com/ (no I have nothing to do with these
folks). I wanted to take the high output fast charge approach on my battery
bank to reduce recharge time. But in reading some of the do-it-yourself
articles I see that the optimum recharge rate seems to be 5-10% of the
ampere hour rating of the battery bank. One article says if you charge
faster you will significantly shorten the life of the batteries. This
system has worked well for me to date, so I am reluctant to modify the
approach if it is going to cause the components to fail more quickly.
From what I can tell from net searches, the batteries are probably 225 AH at
6v, which in series is 225 AH at 12v, and when the two banks are wired in
parallel, I presume I have 450 AH at 12v. So perhaps this all says that my
40a charger is near the max charging rate anyway, and I should blow off the
idea of trying to juice the system to cut the number of hours of noise.
By the way, if you are observant you might also see that at one weekend a
month, I may be able to get along drawing the system down hard but then
letting it recharge with one properly sized PV panel. I would not rule it
out.
Can anyone give me some good advice here please? By the way, the cabin is
in Northern Minnesota.
Thanks,
Tim
Neon John
Here's a very early version of my Cordless Battery Charger.
http://personal.cha.bellsouth.net/cha/j/o/johngd/files/rv/cordless_battery_charger/
This unit charges at 150 amp and as of when these photos were taken,
was equipped with a Cruising Equipment multi-stage charge
regulator. I have moved on to a smart controller of my own design
but the Cruising Equipment unit is adequate if you're around to
monitor it. This is not yet a product, though I could probably be
persuaded to build you one if you twisted my arm and lavished cash
on me :-)
It is acceptable to charge deep discharge batteries at 2C or greater
through the bulk charge stage. The rate will taper down during the
absorption stage. I use the above charger to charge the batteries
on my RV (about 200 a-h) to about 80% capacity in a little over an
hour. Another hour to 90 minutes will bring the battery to
essentially fully charged.
The keys to successful rapid charging include a good multi-stage
regulator and selecting the correct charging voltage for the battery
temperature. Better controllers, including mine, measure the
battery temperature during charging and compensate accordingly.
Ample Power makes a temperature compensated charge regulator but it
is quite expensive. I should also add that periodic equalization
charges are vital to long battery life. Either of these multi-stage
regulators are capable of equalizing charges.
>
> From what I can tell from net searches, the batteries are probably 225 AH at
> 6v, which in series is 225 AH at 12v, and when the two banks are wired in
> parallel, I presume I have 450 AH at 12v. So perhaps this all says that my
> 40a charger is near the max charging rate anyway, and I should blow off the
> idea of trying to juice the system to cut the number of hours of noise.
Not at all. I hate generator noise as much as the next guy which is
what motivated me to start my development project. Given enough
engine and generator, you can easily and safely charge your bank at
500 amps or more during the absorption stage. An hour or so a
weekend should do it for you.
If I was in your shoes, I'd find me a small automobile engine and a
suitable large alternator or two and build me a charger in this size
range. A compact car engine will make sufficient power at a low RPM
and the engine is inherently quiet, being water cooled and all.
Since you're willing to leave it at the cabin, neither weight nor
size matters much. I'm working on just such a generator but for
AC. I'm using a Toyota Corolla engine and a 10 kw belt-driven 60 hz
alternator. Substitute a couple of large truck alternators or an
aircraft alternator and there you go.
You ought to spend some time at the Cruising Equipment
(http://www.cruisingequip.com) and Ample Power
(http://www.amplepower.com) web pages. Though they both tend to
disparage the competition a bit more than I like, both have lots of
good info.
Lastly, I highly suggest you consider getting a Cruising Equipment
E-meter. This meter measures the discharge current from your
battery bank and computes a number of data including a very accurate
estimate of charge remaining.
> By the way, if you are observant you might also see that at one weekend a
> month, I may be able to get along drawing the system down hard but then
> letting it recharge with one properly sized PV panel. I would not rule it
> out.
Minnesota? Solar? Sounds like oil and water to me.
John
--
John De Armond
johngdDO...@bellsouth.net
http://personal.bellsouth.net/~johngd/
Cleveland, occupied TN
George Estep
If you have a place to put it, it might make sense for you to install a
PV panel or two to keep your batteries charged. Here are some rough
calculations, since I don't know exactly where your cabin is:
6 hours * 12 V * 40A = 2880 Wh
2880 Wh/6 days = 480 Wh/day
480 Wh/day * 1 day/4 full sun hours = 120W
So, you can recharge your batteries in roughly 6 days using a 120 W
panel. This is not exact, because you will normally get less than 120 W (in
winter, you may get more) and you will not need to replace as much charge at
the end of the weekend, since the solar charger will be running while you
are there, but it should be close. Clouds could increase the amount of time
before a recharge. On the other hand, the self-discharge of the battery
will be automatically eliminated by the solar panels.
Here are some prices:
Kyocera 120 W module: $569
http://www.partsonsale.com/kyocera.html
Morningstar ProStar 30 Charge Controller with Meter: $186
http://www.solar-electric.com/ps-30m.html
Square-D QO Load Center and Breaker: $30
Wire: $50
Grand Total: $835
This assumes you do your own labor and build some sort of mount for the
panel yourself. As far as whether six days is too long to wait for a
recharge, it's hard to say because I don't know the temperature of your
batteries. If they are in a fairly cool area, then 6 days should be
perfectly sufficient. You may even be able to get away with a 100 W panel,
but I didn't want to increase the risk of sulfation for your batteries too
much.
If you don't have any area of good sunlight on or around your cabin,
this will not work.
Hope this helps,
George Estep
"T Bodin" <TBO...@mn.rr.com> wrote in message
news:k_P57.7378$Uu3.5...@typhoon.kc.rr.com...
George Estep
Sorry, I didn't see the part about Northern MN the first time around.
Here is solar data for International Falls, MN:
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/14918.txt
This shows that you will receive on average about 4.7 full sun hours per day
in June and about 2.4 full sun hours per day in November. This for a
south-facing panel tilted up at around 65 degrees. That means you will
probably recharge in more like 5 days in summertime and around 10 in
wintertime. This will likely be fine, since I imagine your batteries will
be quite cold in November. The only caution about wintertime is that the
sun is quite a bit lower on the horizon, so the shadows from the trees can
become a problem, even if they are not in summertime. (Even small shadows
can greatly reduce the output of a PV panel. It can even cause damage,
though this can pretty well be prevented by using shunt diodes.)
Regards,
George Estep
"George Estep" <gNkOeS...@shentel.net> wrote in message
news:tlg4p21...@corp.supernews.com...
George Estep
Why don't you think solar would work in Minnesota? They have sunlight,
too.
George Estep
"Neon John" <joh...@bellsouth.net> wrote in message
news:3B57DB41...@bellsouth.net...
Lone Haranguer
If you are well exposed to the sun, a few solar panels could keep
drawdown to a minimum. I carry 6 55watt panels in my motor home
for when we park in the desert or at a lake in northern MN. I
also have a wind generator but haven't used it yet. If I recall
it produces 400 watts at 28mph winds. If the cabin is in an
exposed location to wind or sun, either one might be the answer.
LZ
Matt Zilmer
Flooded lead acid golf cart batteries can be charged in bulk or
absorption at 1x to 2x of C, no worries.
Ideas in response to PV use in charging your batts:
1. 100 Watt PV panel would give you about 6 Amps at 12V while the sun
is on it (no shade). Starting assumption uses a single 100W panel.
2. 6 Amps for 7 hours / day (summer), 3 hours / day (winter). This
is a guess. But I'm from northern Iowa and remember how long the days
are in the summer, and how short they are in the winter. You might
want to derate significantly for cosine error that far north,
especially in the winter. During the winter months, you will
probably want to stand the panel mounts up so the PV points almost at
the horizon. Summer will allow you to lay them almost flat that far
north.
2A. summer: 42 AH / day of charging. Drop this to 90%, or 38 AH /
day because of effiency, charge controller, etc. This means you would
get about 0.084C per day during the summer with a single 100W PV
panel. 0.084C for your 450 AH is 38 AH is the per day charge you can
make up during the summer months.
2B. winter: 18 AH / day, and 90% is about 16 AH / day. This would
only charge about 0.036C per day during the winter with the single
100W panel. 0.036C for your 450 AH is 16 AH that you can charge per
day in the winter.
3. Hmmm..... You say you visit an average of 10 times per year, so
it's 5 weeks between visits. If you draw your batts down to 80% of
full charge each time, that's an average 90 AH you have to make up
between each visit. No problem using a 100W panel, and 100W may be
overkill.
4. If you draw the batts down to 50%, this is 225 AH to make up in 5
weeks.
7x5x38AH = 1330 AH charge available between visits in the summer.
7x5x16AH = 560 AH charge available between visits in the winter.
In this best case view, your 100W PV module (qty 1) seems to be
plenty.
5. Cloudy days. Long stretches of them are a problem I would think,
especially in the winter when the days are shorter. You might want to
calculate for a 10 day stretch of 30% output from your PV and see if
you need to scale up to more than a single 100Watter because of this
effect.
However, if you use the figures in #4 above, you get
30% of 1330 AH = 400 AH charge avaialble betw visits in the summer
30% of 560 AH = 170 AH charge available betw visits in the winter
<assumes all days of the 5 weeks between visits are cloudy, probably a
fair worst case situation?>
In this worst case view, in the winter, you don't quite have enough
oomph to restore a 50% discharge of 225 AH or so. Two PV panels of
100W would probably make it up just fine, with a minimum charge
capacity of 340 AH or so between visits.
I suppose you probably don't visit the cabin as often in the winter.
If so, it's possible that a single would cut it. Personally, I'd go
for two 100W panels. Always overengineer if you can afford it (or if
it's someone else's money).
6. You might want to consider snow a problem. If the panels get
frozen guck or snow on them they are not as efficient (probably this
is really bad). Hopefully the 30% derate during the winter would
cover this.
You might want to plan on using the genset to charge, but only during
the winter when everyone is inside anyway.
Good Luck!
Matt Zilmer
Allen Malone
There are certainly lots of opinions around on this one. I'll give you
mine.
I also have 4 6 volt deep cycle golf cart batteries connected as you do for
12 volt.
I have a three stage 100 amp charger (Heart Interface inverter / charger).
I have set the Heart up telling it that I have 400 amp hours (C) of battery
capacity. With those settings it will charge at up to 100 amps during the
bulk charge phase. This is a C/25 rate. Once the battery voltage rise to a
predetermined value that is battery type and temperature dependent the
charger starts the "absorption" phase of the charge cycle and hold a fixed
voltage. The charge current rapidly falls in this phase until it get to a
predetermined value and the unit enters the float phase. The general wisdom
from the battery manufactures that I have read suggests a sustained maximum
charge rate of 10-12% of the battery AH capacity. The information from
Heart and other high capacity multi stage chargers indicates that up to 25%
is OK for deep cycle batteries until the battery voltage rises to a
predetermined level. At that point a fixed voltage charge will rapidly take
the charge rate down to less than 10%. All of my comments are related to
wet cell deep cycle batteries. Gel and AGM batteries have entirely
different charge characteristics.
I have found that running the batteries down to no more than 50% and running
the generator until they are back to around the 85% charge level of the
batteries is the best overall compromise of generator run time. It seems to
take about twice as much generator run time to get the last 15% into the
batteries.
Al
W1QE
"T Bodin" <TBO...@mn.rr.com> wrote in message
news:k_P57.7378$Uu3.5...@typhoon.kc.rr.com...
John H. Mason
battery design. Any higher rate and you will damage the batteries.
Since they are golf cart batteries designed for significant recharges between
use, I suggest a "smart" charge regulator intended for these batteries.
You will find a pretty good tutorial on the subject in a West Marine catalog.
John Mason
Morro Bay California
Freedom, Reason, and Tolerance
Dr Pepper, aka WB6GKI
Please allow me to comment,, , , , ,
First, being an engineer, I truely believe in the old saw, , ,
If it works, don't fix it!
The problem with leaving a valuable genset at a remote location is
that IF it can be stolen, it WILL be stolen.
Which takesd me to another point,, , , ,
I would also recommend an inexpensive hidden camera that sends a
signal to the internet, (assuming that a telephone line is available)
so that you can peiodically check on what's happening at your cabin.
The installation is easy and inexpensive. (email me for details)\
Ron C.
DrPe...@iwvisp.com
===================
On Fri, 20 Jul 2001 06:13:36 GMT, "T Bodin" <TBO...@mn.rr.com> wrote:
Bajadudes
Everyone here beat me to all the impressive calculations so I will just
offer my humble opinion which is........I agree with the solar panel
proposal. One astropower 120W will do you fine. bolt it down as tight as a
clams ass so it won't walk and enjoy the peace and solitude of your cabin.
You and your neighbors will be forever thankful. The sun is a beautiful
thing, harness it and make it your friend. The generator is the devils tool
and while at times it may be fun riding to hell in a handbasket it is best
avoided if at all possible.
Bajadude
NGietz
An observation on the shading from trees... if he's near a meadow or
open area such as a lake, like I am, raising the tilt can take advantage of
light reflected off the snow. I'm about 150 north of International Falls,
and 200W of panels kept me ahead of the game. I was going to my place
almost weekly.
Nelson
George Estep <gNkOeS...@shentel.net> wrote in message
news:tlg6gs6...@corp.supernews.com...
George Estep
Then you'd certainly know better than me. I was trying to recommend an
angle which would work O.K. in summer, as well. BTW, 65 degrees IS pretty
steep. Are you using a steeper angle than that?
One more note for Tim: This may be obvious, but it's probably worth
mentioning: If you can reduce your energy usage, you will reduce the amount
of PV needed or reduce your generator runtime, whichever you settle on. By
this, I'm recommending things like replacing incandescent lamps with compact
flourescents. I don't know what loads you are using, but others may warrant
a change as well. You'll just have to weigh the cost of each against the
cost of the extra PV needed.
Regards,
George Estep
"NGietz" <ngi...@mts.net> wrote in message
news:5%067.552$qf5....@news1.mts.net...
steve thomas
A couple of points:
1. The "C" rate for charge or discharge is based on the ampere hour
capacity at a one hour rate. The 220 a/h capacity rating on golf cart
batteries is for a 20 hour discharge rate. The one hour rate is going to be
less than half this value.
2. Automotive alternator/regulator systems work good in this sort of
application. They will supply a much current as they can during the bulk
phase and taper off as battery voltage rises. Voltage regulation in the
generating system is all that is required for this effect.
3. An engine generator is not going to be efficient when topping up the
last 20% or so of battery capacity as has been mentioned earlier. I would be
inclined to charge up the battery before going home and use a single panel
at 50 or 60 watts to top up the last 20% when not there. A small amount of
overcharge won't hurt that sort of battery and it will prevent sulfation.
Just don't forget to check the electrolyte now and then.
Steve.
T Bodin <TBO...@mn.rr.com> wrote in message
news:k_P57.7378$Uu3.5...@typhoon.kc.rr.com...
> Hi folks
>
> I have a charger/battery/inverter system in a cabin in the woods that i
> visit on weekends. There are 4 batteries, 6v each, wired into two banks
for
> a 12v system. These were the $45 variety golf cart batteries from Sam's I
>
SNIP
T Bodin
i was up at the cabin this weekend, was excited to look for responses before
i went, but couldnt. i see them now and am half overwhelmed and wholly
thankful
couple specific responses to open questions:
1) i am near the town of Moose Lake, MN
2) it is leased land so i have no utility connections to anything, and
cannot do so. so the camera thru the internet/phone is a no-go
3) i have no neighbors that would appreciate the quiet (we are talking
boonies folks) tho i would appreciate it
4) i have an unobstructed south view and a perfect mounting capability (cats
out of the bag)
5) i agree if it ain't broke, dont fix it
6) one other reason i dont want to lug the genny is i bought an older
motorcycle this year; it wouldnt balance well with the genny on the rack,
along with fishing rod, etc
7) i already am using flourescents exclusively, tho i have a toaster and an
electric coffeepot, but use of those could be eliminated. one other juice
sucker is a gas oven; the glow plug really pulls juice i think - anyone know
how to disconnect that or modify it?
i think i will suffer the lugging for now and will keep my eye open for a
used PV panel. i always like to try new things and have studied these some.
if i mount one, say 100-120w, and if i need the genny to juice up on longer
stays, would i need to dismount the PV panel while i add in the genny juice,
or do these components coexist by default in proper isolation?
thanks much for all of your advice
tim
"T Bodin" <TBO...@mn.rr.com> wrote in message
news:k_P57.7378$Uu3.5...@typhoon.kc.rr.com...
Bob Giddings
Just a note, since I have the same battery setup that you have on my
5er. I just got back from a 28 day trip to the PNW. I found my
batteries would get down to about 12.3 V after 3 days sitting in the
same place. It only took 45 minutes with Honda eu1000 to bring them
up to 12.6, and then I was good for another couple of days. This
generator is about $650, and is as quiet as these things get.
Obviously your use is greater than mine, but the Honda 1000i will do
the job, and you won't notice it much.
Bob