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oldspark battery bank w/possible solar


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oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: August 08, 2011 at 9:31 AM / IP Logged  
You're the one that's going to be spending a fortune on batteries, so whatever you want to do....
As to solar panels, I can't see the point. It is a lot of money etc for something that makes little impact on overall consumption.
All I can say is (if I have failed to do so already) is that batteries are only a short-term source of power. They are not intended to provide long-term power for high-power loads.
The alternator has to charge the batteries at whatever is recommended by the manufacturer. That may be 13.6V, 14.2V whatever.
It has to charge them long enough to be recharged (usually capped to 10% of their rated capacity, hence over 5 hours for a 50% discharged battery).
At least to 50% discharge capacity you will only be replacing the batteries every 3 years instead of every year.
But whether they last that long depends on their actual load - those lifetimes assume proper charging and reasonable discharge rates.
Are you sure you have calculated your load (current) and reserve times correctly? It seems too few batteries for such a big load.
meltmanbob 
Member - Posts: 37
Member spacespace
Joined: September 02, 2009
Posted: August 08, 2011 at 10:12 AM / IP Logged  
Why do you say I would be spending a fortune on batteries? $60x4=$240 which is cheaper than a single brand new battery of comparable capacity. Considering I really only need this set up to last me 1-3 years I don't follow you with the idea that I'm going to spend a fortune, did I misunderstand something?
As for the solar panels it is something I'm interested in doing and I don't see how even a 150w panel could not contribute and recover it's cost. $225 roughly for the DIY route for 150w, that would probably contribute around 600-700w of charge per day. I don't know how long that would take using the alternator but ultimately it's free energy that can be taken advantage of while I'm in class and I don't have to waste gas for whether it be by running the van or purchasing a generator and running that.
I guess what I'm asking about the alternator is if I have those 4 batteries drained to 50%, will they draw more power to recharge from the alternator than that 70amp alternator can safely put out? I don't want to burn out the alternator.
I understand that the deeper the discharge the more you reduce the lifespan of the battery which is why I'm leaning towards 4 batteries instead of 2 that way on average I'm only discharging down to about 75%. Also if I have 4 batteries for a capacity of 600ah @ 20hr that's 30amps per hour; 360w per hour. I figure that's pretty close to what I would draw with the computer on, a light and a fan. The computer is the biggest consumer, occasionally I'll use other things, maybe even a toaster oven for 25min a couple times a week. Since you convinced me to do away with most of the electric cooking appliances and the van I ended up with doesn't have an air conditioner most of my electrical needs are gone with the exception of the computer which I don't see as being a high load when considered against 4 batteries that have a 20hr rating at 30amps/hr.
Correct me if I'm miss understanding something.
I'm still unclear as to what you are saying about the alternator, if the alternator caps out at 10% of the rated capacity is that the 20hr rated capacity? With 4 of the 1275's that's 600ah so are you saying the alternator would push no more than 60amps into the battery bank? That doesn't sound like it would be good considering the alternator is a 70-78amp, wouldn't that burn it out? With the 110 wouldn't that be the same as only putting a 20-28amp load on the stock alternator?
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: August 08, 2011 at 12:23 PM / IP Logged  
Solar panels take about 5 years to pay for themselves (used full time). Over 3 years, that is far from free.
The 10% capacity charge rate is dependent upon manufacturers ratings & spec sheets so refer to your datasheets etc.
At 30A, 4 T-145s should last ~16 hours, but if discharged to that level they will last ~1 year.
But I assume no more than 8 hours, hence your ~50% discharge.
To recharge at 50A (2x25A ~10% of C20) assuming 6 hours @ 360W (2.2kWHr) will take about 4 hours.
Alternators should not burn out at full load. (In fact they should never burn out, but that's another story.)
Please restate your load - how many Watts per day that is to run from this system?    
meltmanbob 
Member - Posts: 37
Member spacespace
Joined: September 02, 2009
Posted: August 08, 2011 at 2:40 PM / IP Logged  
I'm not getting T-145's the place here has T-1275's which are 12v 150ah batteries, 600ah vs 520 for 4 145's. I'm figuring between 600-1400w per day so about 2-4hrs at 30 amps which is 10%-20% drain of the 20hr rate, that should be much better than having a system where they are hitting 60%-50% capacity each day. Basically for every 2 hours at 30 amps I'm draining 10%, I doubt I'll ever draw 30amps for 10 hours in a day, maybe the occasional 6 hours. To put it simply and to be safe I'll assume at least 1 hour per day at 30amps to account for everything other than the computer such as a desk fan, LED lighting, radio. Then I figure between 1-4 hours of the computer going which is right about the 30amp draw. Power usage really depends on how many classes I have that day.
Either way with 4 of those 1275's I could draw 30 amps for 10 hours to be at 50% and I don't think that is realistic at all for my usage. 25% drain is 5 hours @ 30amps or 1800wh.
Regarding the alternator I am worried that something would go wrong with it since the 10% C20 rate for 4 of those batteries combined would be 60amps, that leaves a whopping 18amps for what used to be run on 78amps and that's if I'm remembering correctly that the guy at the parts store told me it was some odd numbered amp alternator. With the 110 then that would leave 50amps to do what the stock 78 was doing, not ideal but I think that would be less stressful than trying to run everything that was already in the van from the remaining 18 amps not to mention there is the starting battery that will also draw a decent chunk of power at times.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: August 08, 2011 at 8:40 PM / IP Logged  
FYI - T1275s here are $300 each; list price is $500 each.
When I started this batch of replies, I was referring to your original load - hence the "2.3kW per day". (By which I meant 2.3kW per hour per day, not 2.3kWHr.)
From what I can see, your calcs etc are ok.
T1275s provide 120AH@C5 & 150AH@C20; 102mins @ 56A => 95AH@C1.7 etc.
4hrs@30A = 120AH which would fully drain one T1275 (<120AH@C4) (where "fully" means to Trojan's discharge limit whether it be 50% or 80%), therefore "half end-point" drain for 2 T1275s (ie, 25% or 40% discharged - the data I have seen provides no DoD statement).
So 2 T1275s should last a few years handling that load assuming they get charged every day. (ROT - 80% DoD = 1 year; 50% DoD = 2-3 years; from 200-300 cycles & 800-1200 cycles respectively.)
And being flooded, they can take more abuse than AGM or Gel. (Are you mounting the legally - ie, a ventilated-outdoor space?)
And having 4 will make life even easier for them although, without isolation, I'd probably keep one separate as a spare or as reserve (especially if they were my crankers!)
The alternator should be fine. The question is whether it is big enough to charge the batteries and whether you drive long enough. The cranking power is almost negligible (say 250A for 15 secs = 1AH).
PS - It should be obvious that I refer to 2 lives - hours refers to discharge time & capacities whereas years refers to the lifetime of the battery (usually 80% of their rated capacity).
meltmanbob 
Member - Posts: 37
Member spacespace
Joined: September 02, 2009
Posted: September 01, 2011 at 12:31 AM / IP Logged  
Oldspark - Well as always it's been a little while, I actually just purchased the batteries, 6 of them to be exact. I was just going to make do with 4 but I found out I will be in the van closer to my worst case scenario which means at least for the next 2 years. I'm considering my options a bit differently considering this development but for now the thing I need to deal with is how to mount the batteries and I was wanting your advice if you have any.
I would like to place them all under the van, there are spaces on the driver and passenger sides closest to the outside of the van. They are actually between the frame/bed rails and the sides of the van, the driver side should have enough to put the batteries side to side and the passenger is more narrow so the would have to go length wise. Basically the dimensions I'm working off of on both sides is about 54" long, 13" wide on driver side, 8" wide on passenger and just enough height to have them only show about 2" below the van shell.
Ideally I would think the best place would be as low as possible, centered front to back and side to side. Obviously I can't put them centered side to side because of the drive shaft, I could put some on the inside side of the passenger frame/rail but not on the driver side because of the exhaust.
Any where they go I am most concerned with the mounting surviving the road. I've considered dropping all thread rods from the underside of the van floor to secure uni-strut but I doubt the floor metal is very thick and the all thread will sway side to side. The other thing I would like to figure out if possible is a convenient way to raise and lower the batteries since they are 82lbs each.
meltmanbob 
Member - Posts: 37
Member spacespace
Joined: September 02, 2009
Posted: September 01, 2011 at 12:38 AM / IP Logged  
Something else I wanted to mention was that yes now I am considering a generator go figure! At any rate that purchase if it happens will be a ways off due to finances but I wanted to ask if you had any ideas on how to disassemble it and incorporate it into the underside of the van. Ideally I wouldn't want it to be something someone could just grab and walk off with and it would be nice to take it apart and build it into the underside of the van and tie it into the van's gas supply. What would be even better is to have it on a remote start tied into the vehicle alarm (when I get around to that) so that I could start it while I was in class or studying and when I get back to the van it would have already been charging the batteries. Also if it could be tied in to a charge monitor so if the discharge goes too low when the van isn't running then it would kick on automatically. I'm sure a lot of that is way more complicated that what it really needs to be but it would be interesting to see what it would take.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: September 01, 2011 at 3:10 AM / IP Logged  
I bought a 2.8kVA (~2.5kW) Chonda (Chinese Honda copy) off eBay for ~$210 (compared to new for ~$800 or more). It works fine and even has a starter motor for electric starts.
It also has a dedicated output for 12V which I think is ~10A (1200W).
But it's too big and heavy to carry around, though I'm thinking of adding 2 fold-away wheels and a handle.
A neighbor has a twin-axle caravan with solar etc, and a generator fo backup. He has it mounted on a slide that extends from the front when it needs to be used. Though it's in a green plastic suitcase-like enclosure, I am unsure of its weight. As I recall, it is rated under 2kVA.
I too am considering mounting a 12V 110AH wet battery under a vehicle. It is about 25kg compared to AGM equivalents that are about 35kg.
Whilst my main worry is protection (from rocks and "humping" (or sumping) - I'm a rough driver - I had to de-hump my vehicle last Saturday (ie, get the weight back onto its wheels instead of its floor!), I am well aware of G-forces and effects on a 25-35kg mass.   I'll probably design for a 100kg mass in all directions, with armor-plated base and impenetrable insulation above the terminals...
I don't see the need to charge the batteries if you are about to drive or start up the PC etc. Charging should be done ASAP after discharging.
And if you have a low-voltage sensor to auto-start the generator, then that looks after that.
But auto-starters IMO should have timers and other lock-outs. I think I last discussed that with another the12volt... er... um... poster that was proposing a self starting car when his audio flattened his battery at barbeques etc. [ LOL - I must find out his progress - he was a self claimed "master of innovation" (or similar) and saw no problems or issues... ]   
A simple system could involve a ~$20 MW728 "battery protector" whose output energises an SPDT relay that closes the generator's starter circuit when it is de-energised (ie, when the MW728 shuts off its +12V output due to a low battery of ~11.2V). (Be aware of the MW728 load (~10mA?) and relay load (30-250mA?) when monitoring the batteries.)   
But how to sense when the batteries are full - or reasonably full - (ie, battery current sensing), or the solar takes over, is trickier. I suspect many use a timer instead - provided that have an appropriate regulated charger (ie, not above 14.4V or whatever suits the batteries).
PS - "generator - go figure...". I have. Compare a 3kW genny to the cost of a 3kW solar installation - ie, probably 1kW to 6kW of solar panels, plus lots of battery reserve. The NEW price of my ~3kW generator would only buy 0.2kW of solar panels. Solar is NOT cheap. Like I say, the panels alone still take an average of ~5 years to recover costs assuming full-time use.
meltmanbob 
Member - Posts: 37
Member spacespace
Joined: September 02, 2009
Posted: September 02, 2011 at 3:22 AM / IP Logged  
I'll look into the generator as $200 is something I could swing when the time comes for adding things but what do you think about getting a used 4 cycle engine in the 2-4hp range and using it to drive the old alternator?
Also please let me know what you come up with for mounting. Basically I want the load bearing supports to be vertical since horizontal would mean relying on the shear strength which is usually much less. I actually had a 1/4" galvanized lag bolt shear off with only about 30lbs of weight on it although it did take about a year the point is I expected it to easily handle the load and vibrations on a vehicle. Also I should mention that in addition to the load bearing supports being vertical I still plan to use horizontal supports as well as some sort of fail safe strap. I'm still at a loss of how to make them easy to take down and put up, I was thinking along the lines of a large trucking ratchet tie down so long as it could take up at least 2' of strap or a ratcheting hoist pulley.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: September 02, 2011 at 7:34 AM / IP Logged  
Don't hold your breath for my mounting - it's intended for a vehicle that I was going to get going in 2005. The cleaned and prepared engine block is still rusting way on my patio!
Alternators and engines have been married in the past. Google or search youtube etc.
I've been intending to find a thrown out washing machine of the belt & boxless armature type (else use my washing machine) as an ~300W wind turbine. (Not to mention a solar fridge!)
I have seen wind generators made from (Volvo) discs etc with added magnets. (Some forum somewhere, or maybe youtube.)
And I knew a guy that challenges conventional wisdoms and posts DIY solutions etc. Try searching for Aussie50 & EdSystems. I'd expect he'd have generation stuff (it been a few years since I spoke to him)
Of course some systems are for AC (230V, 120V etc) whereas others are for DC (12V etc). Direct DC for batteries might be cheaper and simpler (with common alternators etc) and largely speed independent - though paralleling of alternators may have issues - but higher-voltage AC may be more efficient albeit with later AC-DC charger conversion inefficiencies.
Yet again, have some idea of what power you are looking for. That's probably your main search key (your key search key LOL).
Add 10-30% for later conversion inefficiencies if applicable, but I expect you'd be rounding up your requirement anyhow (ie, to suit what is available or offered).
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