Those of you who use a separate battery (but which is also charged by your van alternator when the main battery is full) - what size in AH do you use and why?
110 amph. Why? Because its enough for our day to day requirements.
How many liters of water a day do you use on average? Whats your flow at the brush head in liters per minute? Dividing usage of water a day by flow at the brush head will give you a good idea of how long the pump has run that day.
If we work an 8 hour day doing residential, then we expect to spend about 1/2 that time cleaning the glass. So the pump will run for about 4 hours. (That's our experience. We spend more time on the glass doing large commercial work so we expect to use more battery power.)
With a digital controller our Shurflo pumps draw about 4.5 amps each. 4 hours at 4.5amps = 18 amps.
So a full 110 amph leisure battery will be left with 92 amps with one pump running. 2 pumps running will draw 36amps leaving 74 amps in the battery.
74 amps is about 75% charged roughly.
We don't travel very far so the alternator does very little to charge the leisure battery between houses and on the way home. Today coming home the battery was being charged at 7.5 amps for approx 15 minutes. So we used approx 27 amps but only replaced 2 amps. So we are down by 25 amps today.
If I leave the van alone for another few hours and look at the voltmeter, I will probably see that the battery reads 12.6v so would be about 75% charged. Tonight I will plug in my leisure battery charger and leave it on all night.
In the summer I usually charge my leisure battery every second night, but in the winter I will charge it every night when I put the heater in the back.
We've had 2 single operator vans and in each case an 85 amph leisure battery was more than enough. The second van did a lot more mileage and SIL didn't have to charge his battery as often as we have to.
BTW, its not about how far you travel a day, its rather how long it takes to get there. My van charges the leisure battery the same on idle as it does 'bombing' down the motorway. In other words, if it takes 5 minutes to travel 5 miles then the battery will get 5 minutes of charge. If it takes 60 minutes to travel 5 miles then the battery has received 60 minutes of charge. The distance travelled is the same.
The other interesting thing about alternator charging is this;
If I go out with a fully charged leisure battery and run the pump for 10 minutes, I would expect to have used about 3/4's of an amp (0.75). Although I was drawing current at 4.5 amps my alternator will probably only replenish that at 1 - 1.5 amps an hour dropping to about 1/2 an amp. The fuller the battery gets the slower it accepts a charge. So 10 minutes work could take a lot longer traveling time to replace that; maybe an hour or so.
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