Pretty soon now, we'll be spending some time in an urban area with no RV parks, for work purposes. We need to run some electrical equipment off our house batteries. I thought we'd be able to recharge at the place we're doing work for, but just found out we can't.I'm kind of scratching me head about how to handle this. We don't have a solar setup, and a genny is out of the question in the city.Do battery shops recharge batteries? Big ones? Or is there some other resource I don't know about?We'll be using around 50-100aH a day, I guess. Usually closer to 50-60. We have 200aH in batteries, so it would be best to charge them every night, or at least every other.Thanks to anyone who has suggestions!

Will a vehicle be present? Use jumper cables and assist the throttle on the vehicle to raise RPM's.

Your built in generator. Why do you question not being able to run the generator because you are in a city? That seems weird, and it is no more noise than a lawn mower.. . You should be able to run the generator during the daylight hours. What do you plan on powering?If it is a skillsaw, it can draw 15 amps per hour at 120 volts, or more than 20 AH per day - even with only a few dozen 30 second cuts! Do you need to also recharge cordless drill batteries?My suggestion is to plug in all the cordless drill batteries and run the generator during lunch or shortly before or after, and also run power tools at the same time. The RV charger should put out around 35 - 45 amps per hour, but usually only the first hour is at the full rating, then it will drop off quickly. While your battery has a "Lab" rating of 200 amp hours, don't expect to get more than about 100 AH out of them. What is the largest load that you plan to run? That will dictate the inverter size. You need to locate the inverter near the battery, but not in the same compartment, as the battery gives off hydrogen and that is explosive and also can corrode the inverter circuit board material. Most construction sites do have a 120/240 volt electrical panel to run the construction equipment. Normally they would also have a bunch of extension cords running everywhere. What about the neighbors? Can you get power from them? It might be possible, but you probably will not find out until you get there, perhaps invite them to a Saturday BBQ to get to know the neighbors, and spread some good will. This can do a lot to help improve the site security, as after having a BBQ with you and the construction group, they might be more likely to call the cops if they hear someone packing up the construction materials onto a truck at midnight! If you really could not use the generator, then consider at least 500 watts of solar panels. Try this website. SunElec.com You can write back about the size and number of tools, and perhaps get a idea of how much power you will really use each day. How large of a project? Remodeling 500 square feet or building a 2,000 square foot home? It makes a huge difference! Home Power Magazine has written articles about construction site solar generation to power all the construction tools and equipment. They used 6 golf cart batteries and a 1,000 watt solar system. As the house was getting closer to completion, then the main house 2,500 watt system was also connected to the batteries, and all worked together to run the tools. This eliminated the need for running a generator. Good luck on your project.Fred.

Time to go solar. 400 to 600 watts is not all that difficult or expensive.Otherwise a local gas station that does service can do a recharge and I think you will find it expensive.

I see I should have explained more :).We don't have a standard RV -- it's a self-built project, and we don't have a generator. Didn't think we would need one :/.We'll be in a dense city. Not a place where people have lawns or lawnmowers.The batteries are AGM, so no concerns about gassing. They are 2x50aH and 1x100aH, so they need quite a few hours to charge. We could get a generator, but I really don't think it's realistic to run it for 5+hours...and it would have to be at night, mostly, as we will be using the batteries during the day.It's not a construction job; I don't know what gave that impression. Some auto work and stuff, running hoists, etc.@smkettner Is that a typo? Did you mean INexpensive? Or not?

100AH in AGM batteries can be replaced to 90% in a couple of hours with a 50 amp or bigger charger. My truck has a 130 amp alternator and would have them back to 90% in a couple of hours or less. Otherwise, auto repair shops have chargers.

Battery charging service? | Good Sam Community

31 Replies

JiminDenver
Explorer II
Oct 09, 2014
Naio wrote:
JiminDenver wrote:
1 per AH is one standard. I use 2 per AH but I use mine differently.
You can get 200 kits that a bit more effort for.$300 or less. You would have to put the 4 wires in their slots and add your own legs, hinges and battery clamps.

What is the 100watt kit you used? A very QUICK google shows some at around $350, butI am guessing you found a better deal?

Naio

I build my own kits with panels I find on craigslist stupid cheap. they are install leftovers, dealers closing. etc. To them I add a $100 MPPT controller, $50 worth of wiring and a few pine slates as legs. Each one becomes a very powerful portable although a bit of a pain to handle and store.

This panel cost me $50, so the 230w kit cost me under $200.

You can see how I use my fancy legs here.

So the 200w kit for $300 wouldn't be that hard to make into a portable kit.
JiminDenver
Explorer II
Oct 09, 2014
Here is the ebay search for folding solar kits.

click

100w kits start at $189 including shipping.
120w kits are $235 including shipping
150w kit is $299 including shipping

There is a 200w kit but they want $500 for it when the basic kit with out the hinges and legs including shipping is only $299. I believe muddydogs just had a thread on one of these kits.
time2roll
Nomad
Oct 09, 2014
Here is a source to compare:

http://www.solarblvd.com/Solar-Panels-&-Systems-12-Volt-Solar-Kits/c1_272/index.html
Naio
Explorer II
Oct 09, 2014
Ah, I see on eBay I can get them direct from China for about $150. Is that what folks here are doing?
Naio
Explorer II
Oct 08, 2014
JiminDenver wrote:
1 per AH is one standard. I use 2 per AH but I use mine differently.
You can get 200 kits that a bit more effort for.$300 or less. You would have to put the 4 wires in their slots and add your own legs, hinges and battery clamps.

What is the 100watt kit you used? A very QUICK google shows some at around $350, butI am guessing you found a better deal?
JiminDenver
Explorer II
Oct 08, 2014
1 per AH is one standard. I use 2 per AH but I use mine differently.
You can get 200 kits that a bit more effort for.$300 or less. You would have to put the 4 wires in their slots and add your own legs, hinges and battery clamps.
Naio
Explorer II
Oct 08, 2014
pnichols wrote:

That was an outstanding post! Simply stated, clear, and right to the point.

It was indeed! Thank you so much, @westend! So, I don't need to think at all about stepping down voltage from flooded under the hood to AGM house? That's a lot simpler...

I might add that another inexpensive source of large cabling for use in RV battery setups is jumper cables available in any auto parts store. The clamps on the ends can be cut off and replaced with the heavy duty bolt-on lug connectors available in the same stores.

Yes, that's what I ended up doing for my last project. Most jumper cables are CCA these days, though. IIUC, that is ok if not connecting to pure copper wire anywhere in the run, but unadvisable if we are. I found some pure copper, so I used those.

JiminDenver wrote:
With small pre made portables you simply open up the panels, fold out the legs and clip the leads to the battery. I wired up a simple portable panel/controller/battery set up this morning in under a hour.

I did not realise it could be so easy :).

I read last night that I should figure approx 1watt of solar to 1aH of battery. But I'd had the impression from research a few years ago that it would take much more than that. Maybe I am mixing up full charge with partial-charge-better-than-nothing?

For 200aH of batteries, how many watts solar would be worthwhile at, say 2 hours of direct sun per day and a bunch of hours partial sun?

You folks all are awesome, and I sure appreciate the help!
pnichols
Explorer II
Oct 08, 2014
westend wrote:
On a SPST solenoid isolator, one large post is connected to the chassis battery (+) terminal, the other large post is connected to house battery (+) terminal, one small post is marked for vehicle ignition "on", one small post is to vehicle ground.

When vehicle ignition is turned on with the key, the solenoid opens and the circuit is complete between the chassis battery and the house battery. The vehicle's alternator supplies current to the chassis battery and the house batteries. When the vehicle ignition is off, the circuit to the house batteries is interrupted and no current is exchanged between house batteries and chassis battery.

This is the simplest and most reliable battery isolation switch and doesn't drop any voltage like happens with a solid state isolator. There is no worry for the vehicle's alternator to over-charge either the chassis battery or your house batteries as the alternator has it's own internal regulator. As charge increases to the house or chassis battery, the regulator lets current flow to the batteries until they are fully charged. When the batteries are fully charged the alternator's regulator interrupts the current flow to the batteries, only providing enough current to operate the vehicle.

It's advisable to install larger cable (4 ga. is good) from the battery to isolator and isolator to house batteries. You can get by with smaller cable (say, 10ga or 8ga) but with larger cable, you'll have less voltage drop and your house batteries will charge quicker.

You mentioned that sourcing wire was problematic in your area. A source of good, inexpensive, larger cable is a welding supply shop. A source of lugs to connect everything is an auto parts store. A supplier that has everything and can build cables to any length and size is Genuine deals. The isolator ignition and ground terminals can be wired with any automotive service wire in 14 ga. or larger.

That was an outstanding post! Simply stated, clear, and right to the point.

I might add that another inexpensive source of large cabling for use in RV battery setups is jumper cables available in any auto parts store. The clamps on the ends can be cut off and replaced with the heavy duty bolt-on lug connectors available in the same stores.
DougE
Explorer
Oct 08, 2014
When cool, my Yamaha gas tank vent can be closed taking care of the fumes issue. Gas containers close the vents too so you can put these items inside. I'd put these in a storage box on site though. You probably know how to safeguard jobsite tools. Or use a hitch-mounted storage box with a hitch lock.
westend
Explorer
Oct 08, 2014
Naio wrote:
Thank you, @westend, that is extremely helpful!

I am confused about the solenoid, though. Do I wire it to ignition, for the control, and then to alternator and house batteries? Or maybe its own on/off switch, not ignition? But what keeps it from overcharging the batteries?
On a SPST solenoid isolator, one large post is connected to the chassis battery (+) terminal, the other large post is connected to house battery (+) terminal, one small post is marked for vehicle ignition "on", one small post is to vehicle ground.

When vehicle ignition is turned on with the key, the solenoid opens and the circuit is complete between the chassis battery and the house battery. The vehicle's alternator supplies current to the chassis battery and the house batteries. When the vehicle ignition is off, the circuit to the house batteries is interrupted and no current is exchanged between house batteries and chassis battery.

This is the simplest and most reliable battery isolation switch and doesn't drop any voltage like happens with a solid state isolator. There is no worry for the vehicle's alternator to over-charge either the chassis battery or your house batteries as the alternator has it's own internal regulator. As charge increases to the house or chassis battery, the regulator lets current flow to the batteries until they are fully charged. When the batteries are fully charged the alternator's regulator interrupts the current flow to the batteries, only providing enough current to operate the vehicle.

It's advisable to install larger cable (4 ga. is good) from the battery to isolator and isolator to house batteries. You can get by with smaller cable (say, 10ga or 8ga) but with larger cable, you'll have less voltage drop and your house batteries will charge quicker.

You mentioned that sourcing wire was problematic in your area. A source of good, inexpensive, larger cable is a welding supply shop. A source of lugs to connect everything is an auto parts store. A supplier that has everything and can build cables to any length and size is Genuine deals. The isolator ignition and ground terminals can be wired with any automotive service wire in 14 ga. or larger.