Questions/advise for RV electrical system

[zingarofunkart]

Ive searched and not found so here i B:
In the process if modifying a van for RV.
I want to use 2 12 v deep cycle bat in the system (lead acid) stored in the rear of the van.

? #1.... will i need a vent

If i use the van alternator for charging, have an isolation switch to not use the batteries for starting...

?#2.... can i use like # 10 wired to charge the bank and can i use a home lite switch for the isolation sw.

Im using 2 inverters, now one 300 w for small stuff ( laptop, razor) and a 2000w for coffee and microwave.

?#3 with these two inverters side by side will they draw the same amount of current with respect to output ? ie  will i use the same amount of current (battery ) to charge my razor with the 300 vs the 2000, excluding minor differences in efficiencies.
(BOTTOM LINE) if it takes no more current to run the small stuff the i would got to just one  large inverter.

Very interesting site........z

[bob g]

i would not use a common light switch, a battery disconnect switch is commonly available, much better suited and not really that expensive.

i would use something larger than 10 gauge wire, reason being voltage drop will keep the batteries from being fully charged, and if the van is running when you fire up the microwave the wire will get hot, very hot. it will also get very hot should the batteries be low and you decide to flip the switch to recharge while driving down the freeway... in my opinion #4 is about the smallest gauge i would recommend.

yes i would enclose the batteries and vent them to the outside, takes very little hydrogen gas to damage your ear drums or worse   
and the corrosive gasses are hard on interior parts anyway, all this unless you are planning on using agm, gell or vrla batteries that are sealed, even then i would recommend venting to the outside, however they are much safer to live with unvented.

i would use the dual inverters as you plan, the little 300 watt job is probably going to be more efficient at loads under its capacity than the larger one will be at these lower loads.

imho and fwiw
bob g

[tanner0441]

Hi

In  the UK you can buy plastic battery boxes which have lids on they are not sealed but they do reduce the chance of acid leaking onto the floor of the RV. As for switches look at the the amps involved with a 2000 watt inverter.  I have a 95Ah AGM battery on my motorhome and a 1000 W inverter for emergency power without getting the generator out, and even though the house battery is seperate from the starting battery I still keep the engine running when I have the inverter running, though it does not charge as fast as the inverter takes power out . You are looking around 100A per KW, I use 35mm2 cable as short as I can get and relly on the switch on the  inverter.  You may get away with the inverter for the microwave as it is only normally on for a few minutes, but depending on the power requirements of your coffee maker you may be dissapointed.

You don't mention the capacity of your batteries, you may find you only get 10 or 15 minutes from your batteries at 2000W without taking them lower than is recommended. I would also suggest you box the batteries in and vent them outside, if they are standard lead acid they will gas of when on a heavy load.

Brian.

[zingarofunkart]

Thanks for the input.. Im now modifying my plan and am moving the battery placement to closer to the recharge source (engine alt ) and think ill look into some agm style to reduce the gas, and probably use one of those 12 v computer fans in a series with the plastic battery boxes with a p trap type vent into the floor to reduce incoming debris.
Ive just got the van and am unsure of the alternator output but i figured that the requirement for the larger diameter of wire was due not to the load of recharging the batteries but the use of the starter ??
I figured a battery would charge to its max potential reguardless of the size of the wire or the distance from the source : the variable being the time to charge ??
AS for coffee pots. Ive been using a 750 watt  for years with a 1000 wt inverter run via an extension cord from the engine compartment and it makes good coffee!
Thanks again for the replys... additional coments welcom ...z

[definitionofis]

I see this got answered here. I just posted in the other spot.

I guess everyone thinks the car's own charge controller is adequate. Hmmmm.  I still think limiting rate of charge to not blow the alternator might be a good idea. 

And yes the longer wire might waste power and slow the rate of charge but not stop it.

I still think you need a fuse.

[tanner0441]

Hi

The best way of doing it would be a split charge diode. The alternator is disconnected from the car wiring and connected to the diode common terminal, the other terminals are connected to the car battery and the house batteries, this way the car wiring and the house wiring are isolated from each other but both receive charge from the alternator. This stops starter currents being pulled down the feed to the house battery, and the inverter robbing the starter battery so you could get away with something like 16mm2 wire for the charging circuits.

As stated the alternator will not be designed to charge a battery with a 200A load on it, a standard vehicle alternator is probably about 45A. I only use my inverter to run the microwave or 600W kettle for a few minutes. For longer periods I have a 2KW suitcase generator. I used to work on a US built RV called a Fun Mover and that had a 5 KVA generator built in a frame on the side of the chassis, you could run that 24 hours a day.  You could also look at a couple of hundred watts of solar on the roof.  I also have a charger conditioner which is plugged in as long as the RV is parked up or not in use.

You still have not mentioned the capacity of the batteries you are going for. I would recommend you put breakers on every thing you do, up to 20A you can use the little pop out breakers, anything above that you want properly rated breakers, your split charge diode needs to be at least one and a half times the rated output of your alternator.

I hope this helps.

Brian.

[bob g]

split diodes or too light cabling from the alernator to the battery present a voltage drop, this drop will keep the second battery from fully charging.

most car alternators reduce the charge voltage and current when they get hot, to something as low as 13.8vdc,,, if you have a 0.7volt drop via a diode then at best you have 13.2 vdc to the battery, if the cable is small you could have as much or more loss.. then you don't have enough to charge at all.

large cable and a switch or a relay that drops out when the engine is not running, even then you will want to check to see just how much voltage you get to the remote battery, so see if it will charge in a reasonable length of time, or at all.

if your alternator has a remote sense wire, you could connect it via the relay (second set of contacts) to the rear battery, this would tell the state of voltage at the remote battery and keep the alternator up to sufficient voltage to recharge effectively.

just something to be aware of, probably a good idea whatever you do is to be sure and put a meter on the remote battery to confirm that it is getting enough juice to charge it properly.

bob g

[tanner0441]

Hi

I have fitted plenty of split charge diodes the advantage is, because the alternator is not directly connected to either battery, if one battery becomes fully charged the second  battery will take a charge without robbing the charged battery. Yes the cable needs to be sized for the current it is expected to carry, but I have never had a situation where either battery would not charge. On twin engine installations we fitted two split diodes, or a twin unit, and some fancy switching so either engine or both running together would be charging the batteries.  Three engines had really fancy switching but the principle was the same. The engine batteries were normally 110 AH to 150 AH, the house batteries could be up to four of the same batteries in parallel, and the alternators apart from being marinised were the same rating as standard vehicle alternators. Volvo alternators also had diodes in the field circuit to isolate the tacho feed from the batteries.

I still don't think hi power inverters are the way to go for regular use on vehicles with 12V systems, no alternator or charger is going to cope with a hundred plus amp discharge.


Brian

[birdhouse]

depending on the make and model of the van, it could have a 100A plus stock alternator.  many US make trucks and vans have over 100A alternators in them as stock.  i would think that with the correct size of cable, two deep cells could easily be charged from the vehicle. 

just some thoughts

adam

[zingarofunkart]

Thanks for all the replys... If google is correct my alt is 160 amp. Im revising my plan to use an AGM of around 100 ah and connecting it to the ship batt with # 4 cable with an isolation switch. Those optima batts sound good? again should i use a vent? I got my 2k inverter today from ebay $109 it should power my 700 w microwave.

Again being new here im wondering if a 7 wt solar panel can b hooked up to my batt bank without a charge controller for additional top off current?

thanks again for the replys... z