Q- How to calculate 12V Caravan Usage – Customer Example (Rods calcs in Italics)
We watch some DVD/ TV@ 60 w, x 4 hours
60W x 4 hrs = 240 Watt Hours (WHr)
all lights are LED 4 amp x 4 hours
4A x 12V x 4hrs = 192 WHr
7 amp shower pump for approx 15 min day
7A x 12V x 0.25hrs = 24WHr
, Using a 600 w pure sinewave inverter for 2 x phone charging 4 amps & computers 8 amp = 12 amp day, plus extractor fan while cooking.= 1 amp. total amps @ 12 v = 38 amps
Lets assume 1 hour average usage per day for all: 38A x 12V x 1hr x 1.2 (inverter efficiency loss) = 547 WHr
TOTAL Consumed Watt Hours per day = 240 + 192 + 24 + 547 = 1003 WHr
Charging by 180 w solar, + 120 w foldout when needed.
180W + 120W = 300W max x 4hrs average insolation = 1200 WHr. This is cutting it fine I would say.
Battery Storage required for 2 days of no sun: 2 x 1003 = 2006 Whr
Battery Amp Hours @ 12V = ( 2006 Whr / 12V ) + 20% spare = 12V 200Ah Voila !
Q- Does Temperature effect the total discharge rate? Hot weather vs freezing.
A- The battery voltage will sag more under load in cold conditions but it will still deliver most of its Ah capacity.
Q- Is the charging pack and bms water resistant?
A- Yes, we make the 12V battery modules with covers and seal the edge to prevent water/dust ingress. It won’t handle getting rained on directly though so must be inside the cart.
Q- A lead acid battery gases while charging, does lithium emit anything?
A- Nothing under normal charging/discharging.
Q- What safety concerns do we need to be aware of in the event of a short circuit or heavy impact to the battery pack in the event of a crash or failure?
A- LFP batteries contain an organic electrolyte which is mildly flammable. In the event of a catastrophic short circuit or accident where the batteries are ruptured there is the potential of a fire. A small dry powder fire extinguisher is recommended near the pack.
LFP batteries are much safer in this respect than Lithium Cobalt and Lithium Manganese.
Q- Does the BMS control over discharging?
A- The BCU-PPAK has two protection modes. The first is that it monitors the overall pack voltage and if it goes below the limit (about 90% discharged) for more than 15 seconds the battery will be disconnected. The second is that each cell is monitored so if any cell becomes over-discharged the battery will be disconnected.
Q- If 70% discharge = 2000 cycles we would not want to discharge any lower than 70%.
What lets us know when the batts reach 70% discharge?
A- For this a SOC amphour counting type meter is required such as the Xantrex Battery monitor. It can generate an alarm at 70% discharge to warn the operator to limp home. We are also working on our own battery monitor but it is not in production yet.
Q- Is lithium recyclable?
A- Yes, all the battery components are valuable and recyclable. In future this will be a big industry.
Q- Lead acid batteries sometimes have cells fail. Do Lithium have any failures?
A- Occasionally yes. In my experience about 1 in 5000 cells will fail. In most cases it will be DOA so is easy to pick. Subsequent to installation failures in my experience are due to over-discharge because of installer or operator negligence. That is why we are now supplying the prefabricated 12V EV Power Paks with BMS installed and insist on a BMS master unit being correctly installed. We are moving towards a plug-and-play system which is very robust.
Q- What’s the maximum amperage @ 48volts that the Lithium pack can handle?
A- For a 180Ah system it would be 1800A in short bursts or 360A continuous. 145A continuous is recommended for long life. Your carts would not draw anything near this except when accelerating/pulling heavy loads.
Q- When the Lithium pack is exhausted can we just replace the battery or do you need to replace the bms and charger as well?
A- Just batteries. I think you will find that once they are installed and run in, if they are not abused by running flat continuously they will last a very long time (5-10 years) without any maintenance.
Q- Are lifepo and lifepo4 one and the same battery type?
A- Yes, Lithium Iron Phosphate, or LFP. Not to be confused with LiPoly which are Lithium Cobalt Polymer cells.
Q- Does battery height dimensions include the terminals?
A- Yes, but you should confirm if space is tight.
Q- Is the BCU the BMS master unit you refer to in the “FAQ,s” or are these different?
A- Yes, Battery control unit = Master Unit
Q- what is the warranty period on the batteries and BCU?
A- 12 months from the invoice date on battery and BCU assembly. 36 months on the cells themselves if we can show the cell had a manufacturing fault.