FAST FRED (63.215.227.142)
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Votes: 0 (Vote!) | | Posted on Tuesday, July 17, 2001 - 8:42 am: | |
There is some confusion on the use of an 8D as a house battery.
8D is the size of the case the battery ,like 40R in a suit or 10EEE in shoes or "D" cell in flashlights.
8D is meaningless as to how the battery is constructed,, and its the guts, not the case size that detirmines the usage.
Starting batts are like "Sears DieHards" made to deliver the max cold crank amps to your beast to get started in very cold weather.
IF you live somwhere in "below freezing land", you will want TWO fully charged real starting batts to wake up that DD .
RV MARINE are compromise batts that have a heavier construction than start batts.The plates are thicker and the space at the bottom of the plates is larger to accept chunks of slough off the plate surfaces.
The plates are usually thin enough to give a fair starting voltage ,, and thick enough to be moderatly discharged, without early distruction.
These are a great choice for the coach with NO house system,, that starts and overnites on one set of batts.
They will die if cycled too deeply , no more than 40% down ,then recharge.
REAL Deep Cycle batts can be discharged to the 50% or even 60% with only a small loss in service life.
These if real deep cycle will have to be special ordered from a mfg.
Surette or Trojan are two good brands.
They will never be sitting at the local truck stop or K mart.
Deep cycles will work very well as starting batts in a warm location , but dont have enough surface area to hold the voltage up in a zero day start.
Whats the "best" system depends on the design of the coach systems.
For boondockin I prefer real start batts and real deep cycle batts seperated with a simple charging relay ,, standard RV style.
There are 200A relays ,,or 3 RV cheapos in parallel will do the job{relays should match alternator output}.
For the Weekend Warrior a set of RV Marine "should do the job, particularly if a gen set and BIG {backside of a good inverter} charger is installed,, or if the coach lives with air cond and the batts live the easy life.
Thje question of using a bunch of series 31 or the std. 8D is a matter of what your coach needs in the two most difficult conditions.
First is starting in the real cold with OUT a block heater.
IF Starting Amps is the key , batterys with loads of thin plates {like a Sears diehard } will work best , adding the cold crank amps will tell which is the winner.
My big buck Marine Surette shows 31 with 700CCA and the Starting , NOT deep cycle 8D as 1130CCA
Three ser31 are 59lbs times 3 for a weight of about 180 lbs. and 2100CCA
Two 8D at 158 each is 320 lbs total and 2260 CCA.
The batts would seem to be about equal for a short cold start ,
but if the batts were used at all to power the coach lighting or on a coach with NO house system the 8D would surely last lots longer.
The extra lead is usefull only if you want to RUN dc loads from the set, and doesnt help the cold start , except the 8D will give more starting attempts before going dead.
:" Ok, seems I've been misunderstood. I intend to dry camp for several weeks at a time. I understand from boat people that engine powered d/c chargers work excellent at charging batteries. How about this same unit on a bus? Hope thats clears up my question."
You have to understand the RV folks are locked into reproducing what they saw years ago at some RV show.
Therefore their only concept of a gen set is to run an air cond set or 2 or3 or 4 .
If YOU need air cond , a big stinky gen set IS about the cheapest and easiest way to do that.
A DC alternator does charge any battery bank better than a battery charger ,, ESPECIALLY if the batt set is of a really good size.
IF you had 6 big batts rated at 225A , after a couple of deep cycles the batts will loose about 20% of there cycling ability , so 225 X 6 =1350A you paid for.
With a 20% reduction ( assumes high quality batts } you will have about 1080A of rated capacity.
AS youare deepcycling the bank lets say you go to the 60% charged reading on your E- meter {or with a temp compensating hydrometer}, the bank can be charged at a rate of C-15.
This is 15%of the total batt capacity.
15% of 1080 is 162 AMPS
or 15% of 1350 is 202AMPS ,
somwhere in there is the FASTEST charge rate that the bank will handle.{BULK charging }
AS the acceptance rate will taper off as you get to the 90% full batts the charging rate will go down a bunch.
Most folks get tired of the stink and noise and seldom charge over 95% ,
unless going down the road for many hours, or plug into a campsite.
IF you will be having a really large bat set , and dont need air cond , a 200+ Amp gen set will produce the best charge for the batts , in the LEAST amount of time.
A good 3 step regulator will keep track of the temp of the batts and let you charge well and quickly.
The problem with doing this with a charger is two fold.
There arent any 200A chargers that are sitting on the shelf , a great inverter , is a great charger too, but dont usually get yp to the 200+Amp area.
The second hassle is that for some reason the inverters will not produce as many DC amps on a gen set , as they will on "shore" power.
I do not know why.Somthing to do with peak voltage rather than RMS , but thats for somone else
So if you really want to "anchor out" and live sans air cond ,
with a large set of batterys ,
and you want to keep the batt set working well for 10 to 12 years , YES a dc charging setup will work the best.
BUT you will need a good 3 step voltage regulator ,
and a method of actually measuring whats left in the batt bank{E-meter or equal}.
A Pulse Tech plate desulfator would be good insurance,too.
The boat folks used to alternate between two sets of house batts, but today we know that ONE big set lasts longer,, although you need a seperate starting battery for the engine.
The best House system would be 6 two volt cells wired in series for mega thousands of amps , if you could figure how to recharge , in a reasonable time.
FAST FRED |