Let's build a system - Batteries first

Hi All - I've been reading for a while and gleaned some great knowledge here. Thanks!

I have a 20' travel trailer. We always dry camp. Right now I have 2 interstate batteries - one came with the trailer the other I picked up from WalMart.

We usually drive about 6 hours to camp. We usually stay out 4 days. As a rough estimate the current batteries have about 108 ah - TOTAL. If I assume a 50% dod over 4 days that means I consume 13.6 ah / day. Not a lot. BUT it's getting colder and we'll want to run the furnace. My wife likes the stove fan on when she's boiling water. The small things add up.

I started looking into solar to 1) extend past 4 days and 2) use more power. In looking at all my options I ended up back at the batteries.

I'm leaning towards Lifeline GPL-6CT. I also looked at Trojan T105's. Here's my thinking:

Lifeline:
Cost = $343.20x2 = 686.60
ah = 300
50% dod = 150 ah
Lifetime ah = 150 x 1000 cycles = 150,000
Cost / 10000 ah = $686.60 / 150,000 * 10000 = $45.77

Trojan
Cost = $150 x 2 = $300
ah = 225
50% dod = 112.5
Lifetime ah = 112.5 x 300 cycles = 33,750
Cost / 10000 ah = $300 / 33,750 * 10000 = $88.88

It seems that because the AGM batteries can cycle 1000 times versus the 300 times (at 50% dod) for flood cells the AGM are 1/2 the lifetime cost of the Trojans even though they cost twice as much.

Is this a reasonable interpretation?

Also, I ran the numbers for an Exide Nautilus gold and came up with a Cost / 10000 ah of $79.42.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Let's build a system - Batteries first

    Exactly how I would figure out costs over time when comparing batteries...

    Some better deep cycle flooded cell batteries should last longer--some of the large forklift style are rated out to 2,000-4,000 cycles. Don't know if you could find anything in the smaller battery sizes.

    Also, I would do the pricing in $/kWhrs--sort of gets the numbers into terms that we generally use to purchase electricity (home power is around $0.10-$0.35 per kWhr... Also quickly tells me if I made any mistakes in assumptions (if the price/kWhr is >>$1.00 or way under $0.10 per kWhr)

    Taking your numbers:

    $686/(150AH*12v*1,000 cycles*1/1,000wperkWhr)=$0.38 per kWhr
    $300/(112.5AH*12v*300 cycles*1/1,000wperkWhr)=$0.74 per kWhr

    You can also use these numbers to justify solar vs generator power if you do a lot of camping (near constant use over a decade or two--or if the generator noise bothers you). Fuel costs are around $1.00 per kWhr for a Honda eu2000i class genset... Solar panel + Charger Controller costs, if spread out over 20 years and the system is used much of the year, can be below $0.50 per kWhr.

    Another advantage for AGM batteries (at least Concord claims) that they don't have sulfate hardening issues--so you don't have to charge them right away after they drop below 50% State of Charge...

    Normal flooded cell batteries need to be quickly recharged when below 75% state of charge--or their overall life will be much shorter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Let's build a system - Batteries first

    Of course - kWhr! That makes sense. The next part that I haven't been able to noodle through is the charging wiring.

    I'll have 1) the alternator from the car; 2) shore power converter (an IOTA 2 stage charger I believe); and 3) PV Charge controller.

    How are all three wired so you don't have 36v going to the battery - as in all three on at the same time?

    I don't even really understand what happens when I'm plugged into shore power AND the trailer is connected to the car.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Let's build a system - Batteries first

    Think of the Battery as the "center" of your system... You can connect multiple 12 volt loads and chargers to the battery--and each, more or less, thinks it is the only device connected to the battery...

    For example, you have 3 charging devices connected to the battery. Each is measuring the battery and deciding if it needs charging or not... And each will supply the current, it believes, is necessary to recharge/float the battery. The chargers are all wired up in parallel, and therefore, voltages do not add (stays at 12 volts), only the current from each charger can add (but unless the battery is near dead, is it unlikely that each charger will be putting its maximum current into the battery--all at the same time).

    Is there issues with have multiple chargers connected to the same battery... Yea, the charging/floating decision will not be clean--mostly likely, the charger with the highest voltage settings will be the one that finishes charging the battery last. Just keep an eye on the batteries to make sure they are not overcharged.

    Details, car alternator should be connected through a battery isolator--so that the trailer does not attempt to charge/discharge the car's battery when the engine is off... 2nd, a car alternator typically charges at a relatively low voltage (less than needed to fully charge a deep cycle battery). 3rd, the long wire run/through batter isolator will typically keep the charging current low from the car's alternator (just a wild guess, but probably less than 10 amps maximum in normal operation).

    If you expect/need the car to really charge your trailer battery, you have two choices, install a 120 VAC inverter in the car and run the cord back to your shore power/alternate battery charger... Or, use a 12 volt to 12 volt battery charger (car 12 volt to battery 12 volt) to properly/quickly charge the trailer battery. Check out this recent thread on RV Charging--if you have not already.

    For long term storage/maintenance charging--you need a 3 stage charger (one that has a "float" stage/setting). Iota, I believe, sells a little add-in board that can add float to your current charger.

    What ever is "left on" for long term storage (solar panel or shore power) should be the one, at least, that has a float setting and a remote battery temperature sensor... AGM's are very easily damaged if overcharged (you cannot add water once they are over charged and vent).

    My little cheat for using a trickle charger on a stored car battery (even 1 amp can boil a battery dry in a couple months)... I use a heavy duty plug-in lamp timer and set it for 1-4 hours of charging per day... 1 hour if an old car with no electronic loads... ~4 hours per day if it has GPS, On-Star, Lojack, etc. loads... So far, this has been my "optimum" cheap and easy maintenance charger--keeps the batteries "fresh" and does not boil them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Let's build a system - Batteries first

    i'm going to attempt to simplify this for you.
    1> all 3 charging sources on at the same time could deliver very high current (not adding voltages, but adding currents as bill said) to the battery during the bulk stage. wally world batteries don't take high current (beyond the 13% charge rate) very well and need high maintenance even at 13% as water levels need checked more often than some of the other batteries out there.
    2> any charging source that does not go down to a float voltage may lead to overcharging or at least excess maintenance by boiling out the water. double check if that iota you have is a 2 stage charger or not because that would indicate bulk and acceptance charge stages and not a float stage. is your controller capable of a lowered voltage for float? the alternator is problematic in that it's voltage doesn't get high enough to fully charge a battery by itself and if a battery does have a full charge on it, like say you charged it up prior on solar, then it too will not go to a float stage.
    unless you know what would happen at any particular time and under any circumstances with these sources combined, it is like playing russian roulette with it and it would need you to be physically supervising it.
  • System2
    System2 Posts: 6,290 admin
    Re: Let's build a system - Batteries first

    OK - so if I understand it right... When I'm going down the road the alternator is going to supply it's voltage and amperage to the trailer battery regardless - because it's unmanaged.

    The charge controller may decide to boost the voltage depending on what it senses or where in it's cycle it is. Is this right?

    Next, should I look at a distribution block for connecting the charging sources and/or DC load to the battery? Or just wire them directly to the battery terminal?

    Should each hot lead have it's own fuse?

    I know this is probably basic stuff - I really appreciate you helping me figure this all out.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Let's build a system - Batteries first
    optimator wrote: »
    OK - so if I understand it right... When I'm going down the road the alternator is going to supply it's voltage and amperage to the trailer battery regardless - because it's unmanaged.
    No.

    The car's alternator is a 1 stage temperature compensated charger (more or less)... It will output around 14.2 volts or so (higher if cold, lower if hot). If the battery is discharged, the current flowing into the battery will be higher. (the voltage at the battery will sag a bit from ~14.2 volts due to voltage drops in the alternator and the wiring harness).

    14.2 volts is too low to fully charge/equalize a deep cycle storage battery--and add the voltage drop because of the ~20' wire run (x2) from the "alternator" to the RV battery--you will not really do a good job of quickly and accurately charging in RV.

    To a degree, unless you have very high charging voltages (and/or a very near dead battery bank), the battery will do a pretty good job of limiting current.

    Read about battery charging (and other information) in the Battery FAQ.
    The charge controller may decide to boost the voltage depending on what it senses or where in it's cycle it is. Is this right?
    Just to be clear--the charge controllers are not "boost" chargers in the power supply sense (i.e., they do not take a lower voltage and raise, or boost, it to a higher voltage). There are MPPT type solar charge controllers that "down convert" from higher solar panel voltages to lower battery voltages--but we can ignore that discussion for now).

    What the Charge Controller does is (typically) set a target voltage level... If the battery voltage is low, the charge controller will also limit current to its rated maximum current.

    To "Bulk Charge" a battery, you want the target voltage relatively high (~14.2-15.0+ volts at "room temperature". That forces the battery to take as much current as fast as it can. The recommendation is that for average batteries, that the charger not be able to output more than ~13% of the AH capacity of the battery to prevent overheating (100 AH rated battery, ~13 amps maximum current). There are batteries that can take more current (AGM, and fan cooled forklift batteries, as examples).

    Also, note that battery voltage fails as the batteries heat up--so a remote battery temperature sensor (bolted to the battery itself) is a very handy safety device--A charge controller can be confused as it sees the current rise instead of falling, if the battery dramatically heats up.

    Note that you may have three different chargers with three very different charging profiles/capabilities. Short term (hours, days) any charger will do OK--as long as it has sufficient/appropriate voltage and current to charge the battery to specifications... For long term storage, there must be some charging taking place (to prevent self discharging of the battery ruining it)--and the charger must not overcharge the battery during storage (typically, lower voltage/less average current required for float charging).

    Quoting from the FAQ (save typing redundant information and me causing more confusion):
    Battery charging takes place in 3 basic stages: Bulk, Absorption, and Float.

    Bulk Charge - The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.
    Absorption Charge: The 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.
    Float Charge: The 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging. PWM, or "pulse width modulation" accomplishes the same thing. In PWM, the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. This may occur several hundred times per minute. It is called "pulse width" because the width of the pulses may vary from a few microseconds to several seconds. Note that for long term float service, such as backup power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts.
    Next, should I look at a distribution block for connecting the charging sources and/or DC load to the battery? Or just wire them directly to the battery terminal?
    If you have a lot of wires--a "bus bar" or distribution block is very handy. The bus bar is connected using very short, low resistance (big copper) cables from the battery bank to the bus bar. Then you distribute from the bus bar through your fuses/breakers/wiring to the loads/chargers.

    If you have a few, smaller, connections, then connecting directly to the battery is OK (again using fuses, breakers, etc.).

    The idea is that you want low voltage drop to the battery--both so that the loads function well, and that the chargers don't see an artificially high battery voltage when charging (which reduces current flow and therefore takes longer to recharge your battery--more of an issue with 13% charge rates vs smaller chargers at 5% or below).
    Should each hot lead have it's own fuse?
    Fuses and breakers are safety devices that prevent shorts in wiring and/or devices from drawing too much current and causing a fire.

    So--any wiring from the battery to a bus bar (for example) should be well protected against shorts... A large Lead Acid battery can output 100's to 10,000+'s of Amperes into a shorted load (actually more current that a shorted 120 VAC wall outlet can supply).

    Fuses and Breakers should be as close as possible to the battery/bus source (on the positive lead)--since this length of wire is not protected against shorts. The output of the fuse/breaker should be appropriate for the size of wire connected (like a 14 awg wire should have a maximum of 15-20 amp fuse/breaker)...

    Whether you run one 15 amp circuit (15a/1.25=12 amps maximum "usable" / "safe load") around to your four or five lights/fans/etc... Or you choose to run 5x 5 amp fused circuits to each load individually is pretty much your choice.

    You should not, in a 12 volt negative grounded system, have any fuses in the return. / ground leads... Also, the sizing of the return lead must be sufficient to handle all of the planned loads/and at least one short...
    I know this is probably basic stuff - I really appreciate you helping me figure this all out.
    On the surface this (fusing, wiring, safety, charging system designs) seems like it should be simple--but many of us have made very good living understanding/interpreting Safety Regulations/Requirements when designing and manufacturing systems.

    Hope this helps. Please feel free to ask any more questions... Also, if you really get into this--a reference book like the National Electric Code (NEC) for those in the US is a handy reference (does not really apply to RV's and such--but since you will be using much of the same wiring and such from Home Depot for AC wiring--it can be very handy). Some libraries may have the NEC--make a couple photo copies of the wire type / sizing/fusing tables.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • banjorene
    banjorene Solar Expert Posts: 36
    Re: Let's build a system - Batteries first

    You vehical alternator shoud have a built in regulator to regulate the output of the alternator
  • banjorene
    banjorene Solar Expert Posts: 36
    Re: Let's build a system - Batteries first

    Forgot to mention in rare casses the alternator can go bad and allow the battery to feed threw the alt. draining the battery it's rare but does happen.
    Remember you have a feed wire on the alternator that remains hot with the engine off.
    If the Alt. decides to go bad it will drain your batteries (most often over night )
    Rene
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Let's build a system - Batteries first
    banjorene wrote: »
    Forgot to mention in rare casses the alternator can go bad and allow the battery to feed threw the alt. draining the battery it's rare but does happen.
    Remember you have a feed wire on the alternator that remains hot with the engine off.
    If the Alt. decides to go bad it will drain your batteries (most often over night )
    Rene

    Battery isolator solves that, but it's been covered that there are better ways to recharge while traveling (120V inverter feeding shore power charger). Just remember to shut off the inverter, when you stop for lunch or fuel.
    Same inverter can be carried from car to trailer, for trailer power, just 2 disconnects, AC & DC.
    DONT think you can run ground thru the frame and hitch - use a ground cable to match the 12V light power cables. (at least 16ga, 14 better).

    Will there be any solar in this system ?

    Where will the batteries live - trailer tongue ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • System2
    System2 Posts: 6,290 admin
    Re: Let's build a system - Batteries first

    Wow! you guys are great! Let me take my questions one at a time.

    So, If I use a bus bar - do I have a fuse between the battery and the bar AND fuses on EACH of the hot leads going to the bus bar?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Let's build a system - Batteries first

    Good Question... I have hardly ever seen a large fuse between the battery and the bus bar... In cars, there is the "fusible link" between the battery and some heavy loads.

    From a safety viewpoint, yes the cabling from the battery should be fused to the capacity of the cable/bus bars.

    Problem is that those type of fuses are physically quite large (and not cheap). For the most part, heavy cables, well supported and protected from sharp/hot objects (etc.) so that they "cannot short" is what I seem to remember.

    There may be a fusible link in "professionally" installed battery banks--but they are sometimes difficult to pick out from the rest of the wiring.

    ...I don't know the "right" answer...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Let's build a system - Batteries first

    Here is some information from the ABYC (American Boating and Yachting Council???)... Anyway, an App. Note from Bluesea:

    Note the warning about fires:
    Electrical shorts are the number one cause of fires on boats. In fact, more than half of boat fires are electrical in origin. More than half of those are caused by short circuits, most in the DC circuits. If you add any circuits to your boat, make sure they are protected.
    Why heavy wiring from battery is not fused/protected:
    Notice that wires intended to carry engine-starting currents between the batteries, the switch, and the starter, are not required to have main-circuit-protection devices installed.


    This exception is based on the notion that the starting battery would have just enough power to handle starting the engine, and the wiring would be appropriately sized such that the full capacity of the battery would be unlikely to overstress the wire. It was also assumed that the batteries would be very close to the engine.


    Some modern installations violate some or all of these assumptions with very large house banks that may include an emergency cross connection switch, making them part of the starting system. The house banks may be some distance away from the engine in different compartments. Some experts believe that all circuits on a boat should be protected - including the start circuits. However, at this time, this is not an ABYC recommendation.
    Also, on the is page, is a recommendation chart of CCA (cold cranking amps) to maximum assumed short circuit current:

    12/24 volt

    CCA 650 amps or less -> 1,500 amps
    CCA 651-1,100 amps -> 3,000 amps
    CCA 1,100 amps or more -> 5,000 amps

    Regarding "how close to place fuse/breaker":
    The ABYC also publishes standards for the placement of circuit protection in the DC main circuit. The goal of overcurrent protection is to provide protection at the source of power for each circuit. With DC circuits, the overcurrent protection is always placed in the positive side. Circuit protection should be connected as close as possible to the source of power.


    Sometimes there are physical limitations to how close a circuit protection device can be placed to the source of power. In any case, fuses, circuit breakers, and switches should not be installed in battery compartments because of the risk of corrosion coupled with the potential presence of explosive gasses. The question then arises, how close is close enough?
    ABYC E-11 recommends that each ungrounded conductor connected to a battery, battery charger, alternator, or other charging source, shall be provided with overcurrent protection within a distance of seven inches (175mm) of the point of connection to the DC electrical system or to the battery. There are exceptions to this seven-inch rule.


    If the conductor is connected to a source of power other than a battery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box, or enclosed panel, the overcurrent protection shall be placed as close as practicable to the point of connection to the source of power, but not to exceed 40 inches (1.02m).


    If the conductor is connected directly to a battery and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box, or enclosed panel, the overcurrent protection shall be placed as close as practicable to the battery, but not to exceed 72 inches (1.83m).
    And this page (ABYC), ANCOR maximum ampacity before insulation melts.

    Anyway, the 7" rule to 72" rules are just that--made up standards that help reduce the risk of fire... (0" would be better--but that is not possible).

    At least something to read about how others have addressed these very good questions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Let's build a system - Batteries first

    Bill - Thanks for the link on the fuses. I never really thought about the difference between overcurrent and short circuit protection. - For me the understanding of "why" really helps when I "do".

    Neil - The IOTA only has bulk and absorption. I can buy an add-on which will give me float - but from the docs it doesn't look like I can change the voltage for a specific stage - which I'd like to do for the AGM type batteries.

    At this point what I'm trying to decide is IF I would need some sort of manual disconnect for the CC.

    I'm thinking about the situation where the batteries are full because they have been float charged by the CC. I then pick up the trailer to load it and plug it into shore power for a day while I'm getting it ready. It seems like I wouldn't want the IOTA charging the batteries at this point because they are full.

    Any ideas on a manual disconnect switch?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Let's build a system - Batteries first

    Many times, the manual disconnect for the Charge Controller is just a properly rated Circuit Breaker... You can also look for Marine switches too...

    I probably would just leave the Iota connected to the battery... Its absorb setting of 14.16 volts for a 12 volt battery will not hurt for a day.

    I would be a bit more worried about the fact it goes into an equalize cycle every 7 days... That could damage the AGM batteries.

    You probably need to contact Iota and ask them specifically about what they recommend for AGM installations.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Let's build a system - Batteries first

    you could use the circuit breaker as bill mentioned to act as a disconnect or if you have a fuse just pull it out with the alternative being a high current dc switch like the blue seas type.