Dual 12v in parallel?

[ShaggyRV]

Is anybody running 2 12v batteries? It just seems to me that it would be a great idea. Your thoughts please.

[waiter]

I assume your talking 2 batteries for the coach instead of one.

Two batteries would give you more time between charging, it depends how you use your vehicle.

In my case, I've found the single battery will run me just about one full day /night of use, i.e. stop for the night, run the microwave 5 minutes to warm up the leftovers. run the lights and TV for a couple hours. run the furnace all night, run the elect coffee pot in the morning.

John Mc

88 Dolphin 4 Auto

[ShaggyRV]

Wow! My coach battery is not being charged by the Alt. I am planning a hunting trip where I'll have no shore power. Don't think I'll have time to get and replace the Isolator. I have a generator but I'm worried that running the furnace all night will kill the coach batt and then I won't be able to start the Gen to get it charged back up/ I've never run the furnace without shore power so I don't know how long the coach batt will last. I don't want to have to run the gen all night though.

[linda s]

Amazon can get one to you by Tuesday if you order by tomorrow morning. replacement takes like ten minutes

http://www.amazon.co...r/dp/B0002UHVYQ

Linda S

[straygoose]

Is anybody running 2 12v batteries? It just seems to me that it would be a great idea. Your thoughts please.

I'm thinking about it. I have the room, as currently constituted. I am also thinking about taking out the enclosure under the sofa and enlarging it to hold four 6v batteries, but I think that the weight issues will keep me from doing that.

[Derek up North]

Amazon can get one to you by Tuesday if you order by tomorrow morning. replacement takes like ten minutes

http://www.amazon.co...r/dp/B0002UHVYQ

Linda S

I'd look under the hood to identify the isolator before buying one 'blindly'. It could be as simple as the 'signal' wire having been cut or knocked off. Or a nut that holds the cable leading to the house battery. And why order a 3 terminal isolator if you need 4 terminals?

[waiter]

Could be almost anything, but I would start the troubleshooting process at the isolator. broken wire terminal, etc.

Another problem that I've heard, take a close look in the coach battery compartment, make sure all the wires are hooked up to the battery. Sometimes there's several wires hooked up to the battery post and one of them gets overlooked.

What year is the vehicle and what model?

John Mc

88 Dolphin 4 Auto

[Maineah]

I agree with Derek unless you like shiny things a full check out would be a good idea. could be as simple as a $3 circuit breaker or a rusty connection. Carry some jumper cables with you you can jump the generator with the truck and recharge the coach battery with the on board charger if it comes down to that. If the battery is charged it should run the furnace over night unless you like it at 70.

[zero]

Is anybody running 2 12v batteries? It just seems to me that it would be a great idea. Your thoughts please.

I've got two deep-cycle 6 volt batteries in series for my RV "house" batteries (225 amp hour). Amounts to the same end-result of having two 12 volt batteries in parallel. Regardless of your choice of voltage, it pretty much comes down to battery weight. Two 70 lb. batteries give twice the run-time as one. Does't matter if it's two 6s in series or two 12s in parallel. A 6 volt battery is just three battery cells in a box, whereas a 12 volt battery is six battery cells in a box.

I've found that my two 6s will run my AC refrigerator for four days with no recharge. I can also run an inverter-type 1000 watt microwave at 80% max heat just off the batteries. If want to run it at full heat- I start the engine so the engine alternator can assist and the microwave works great at max setting.

[stamar]

ya the worst thing that happens in this forum is sometimes people expand on electrical things that have almost nothing to do with the persons questions and confuse.

]

Ha so I set myself up for this.

having two batteries in parallel connected to our isolater solenoid alternator charged toyhomes is the least effecient use of the batteries power.

this is because the alternator has the hardest time putting in the top 10% of the battery, yet with two that top 10% is twice as long now. that battery is a balloon, and pushing the last bit of air in takes the most breath...

so whatever amps our alternator is ( not enough for this purpose at all) suddenly with two batteries its much less amps and more just wasted power.

a real battery isolator that draws from one battery at a time is the solution for long term electrical power.

one last thing...the solar cell has a lot easier time putting its amps fully into the top of a deep cycle cell

[ShaggyRV]

Thanks for the replies. I have a pretty thorough understanding of electronics. I do know that 2 12v batts in parallel should last twice as long. Charging time will double because current in parallel will be split 50/50 to each battery. As far as the isolator goes it is pretty rusted up and I checked it with my meter. Its definitely bad. There is also some sort of circuit breaker or something mounted to it. i see no way to reset that. I will probably just take some long jumper cables just in case as I'm leaving for a boondock hunting trip on Wednesday. I also think my isolator has 4 poles. I will get a pic and post it up soon.

[stamar]

ya what i mean by isolater is different than the relay solenoid we have under the hood.

but a true isolator.

this being an example chosen at random

http://www.amazon.co...attery isolator

something to charge one battery at a time

our toyota 2 battery alternator, solenoid isolater type systems are world class inefficient in charging the deep cycle we have to make a long story short ....and couldnt really handle just the added amps needed to keep pace with the extra battery even if you drive them A LOT every day.

so just to get a step past the orignal question, why put in another battery with the concept of charging it with the alternator? For hooking it to a landline and doing a quick weekend excursion i understand.

before i had led lights i couldnt even keep pace with leaving the lights on and i drive mine about 20 miles a day.

but the first step you should be on is increasing the charging power of your toyhome.

[Bob C]

When my isolator decided to crap out on our vacation this summer, I just started the engine in the morning and reconnected the wire leading that connected the isolator to the coach battery to the terminal leading to the starter battery. It charged both that way. Just remember to disconnect the rear battery at night or you may not have enough power to start the engine in the morning.

It might be the Red Green redneck solution, but, it got me home.

[ShaggyRV]

When my isolator decided to crap out on our vacation this summer, I just started the engine in the morning and reconnected the wire leading that connected the isolator to the coach battery to the terminal leading to the starter battery. It charged both that way. Just remember to disconnect the rear battery at night or you may not have enough power to start the engine in the morning.

It might be the Red Green redneck solution, but, it got me home.

I was just thinking about doing the same thing. I'm going to fab up a jumper wire with alligator clips at work tomorrow. Then I can just put that on to charge it up if the battery gets too low to start the generator.

[Maineah]

ya what i mean by isolater is different than the relay solenoid we have under the hood.

but a true isolator.

this being an example chosen at random

http://www.amazon.co...attery isolator

something to charge one battery at a time

our toyota 2 battery alternator, solenoid isolater type systems are world class inefficient in charging the deep cycle we have to make a long story short ....and couldnt really handle just the added amps needed to keep pace with the extra battery even if you drive them A LOT every day.

so just to get a step past the orignal question, why put in another battery with the concept of charging it with the alternator? For hooking it to a landline and doing a quick weekend excursion i understand.

before i had led lights i couldnt even keep pace with leaving the lights on and i drive mine about 20 miles a day.

but the first step you should be on is increasing the charging power of your toyhome.

Be advised you will lose .7 volts through a solid state isolator no matter how good they are. The standard relay isolators are 100 amp inrush and 65 amp working. The MH charging system should provide you with 30 amp charge rate if every thing is in good shape. I have no issues charging two 80 amp batteries with the stock system. If you need more current to your rear batteries just installing a bigger alternator will not cut it, the coach is wired with a # 8 wire from the isolator it is rated 30 amps to get more to the rear batteries that would have to be changed to a larger size one matter how big the alternator is. The solid state isolator charges both the truck and the coach battery at the same time they are not smart, to achieve that you would need a combiner. Granted if you only drive 20 miles that's barely enough to charge the truck battery. The solid state isolators require alternator rewiring the relay types do not they are the simplest and the easiest to trouble shoot. Both work fine there are draw backs to both. As stated before a simple jumper will get your coach batteries charging in an emergency however you can get into trouble jumping a solid state one if you don't know how.

[stamar]

Ya I can see where each step doesnt do it with out the next step, whereas a battery does something without anything else at the very least if you have the charger and shore power.

Im in the minority I just dont have shore power so the battery needs another step first bercause im also not driving it full time.

Right at the moment my deep cycle is only powering my led lights thats all it does. no more experimenting for me but it covers just that fine.

ya my 2nd battery is still in the planning stages but if wiring it is the biggest concern there is actually 12 volt wiring to the battery running along the couch. that means, put it under the couch. another 8 guage line from the isolator to the new battery, shortest distance possible.follow the one thats already there.

and sure a different relay or none. im not positive i like that thing although it has bailed me out once when i left the headlights on.\

and definitely prevented battery death going the other way when i was experimenting with inverters.

[fred heath]

Just a point for older models. My 1978 has an external regulator.

I tried the sonic solenoid type from the main battery and could only get about 12.5 volts to coach with engine running. Switched to 3 terminal isolater made for use with external regulator. Now get 13.5 or better depending on how low the coach battery is.

All said and done, my coach battery will only run the furnace blower about 6 hours before going to low to run the fan. I like the idea of 2 batteries for the coach

[zero]

Just a point for older models. My 1978 has an external regulator.

I tried the sonic solenoid type from the main battery and could only get about 12.5 volts to coach with engine running. Switched to 3 terminal isolater made for use with external regulator. Now get 13.5 or better depending on how low the coach battery is.

All said and done, my coach battery will only run the furnace blower about 6 hours before going to low to run the fan. I like the idea of 2 batteries for the coach

I don't know exactly what you have for an relay- but a generic relay and it's wiring has nothing to do with an alternator having an internal or external regulator. A relay is just a remote controlled switch that connects the output of the atlernator to the RV battery.

With the coach battery - much depends on what type of furnace and battery you've got. A 30,000 BTU furnace with a pilot light and blower will draw around 5 amps. If it has electronic ignition around 6 amps. If it ran constantly without ever shutting off - and was hooked to a typical Walmart 115 amp-hour battery it would be down to half-charge after running that heater for 9 hours. If the heat cycles on an off halt the time run time should be 18 hours.

I've got a new Suburban 42,000 BTU furnace that was in a Class A motorhome for a few weeks. Blower and electronic ignition. Draws 9 amps when running. Even that monster could run 6 hours on a 115 amp-hour battery.

[linda s]

Just checked and the amp draw for the furnaces used in the Sunraders was 4.4 amps for all models. I have gotten stuck in places where the temps dropped to below freezing unexpectedly and ran my furnace all night with no problems. BUT I had just replaced the alternator. Before that, even before the alternator was giving me warning signals of failure the battery wouldn't last the night even in warmer temps. I'm guessing the old original alternator wasn't putting much power out long before it died and never charged the coach battery properly.

Linda S

[Derek up North]

I think the biggest furnace you'll find in a Toyota is 16k Btuh (or is it 18K?).

[linda s]

I think the biggest furnace you'll find in a Toyota is 16k Btuh (or is it 18K?).

it's 16k for Sunraders according to the brochures on the toyota campers site. Didn't check any other manufacturers

Linda S

[5Toyota]

i dont recall on that but i can run my furnace for at least two nights at 55 without any problem at about 20 or so outside

[Derek up North]

1991 & 1994 Winnebagos had 17,000 BTU, SUBURBAN DD-17DSI, so right around there's about as big as you'll find.

[fred heath]

Not sure what's going on. New alternator,regulator,primary battery,coach battery,coach fuse panel,new coach wiring, no shorts.

Just had to order a new furnace control module. The furnace is original,and appears to have upgraded from pilot light to electric.

The mfg. I'd info is missing. Name on thermo is hydro flame. I should mention the two nights I had to use the furnace,the outside temp was 20 degrees.

[zero]

Not sure what's going on. New alternator,regulator,primary battery,coach battery,coach fuse panel,new coach wiring, no shorts.

Just had to order a new furnace control module. The furnace is original,and appears to have upgraded from pilot light to electric.

The mfg. I'd info is missing. Name on thermo is hydro flame. I should mention the two nights I had to use the furnace,the outside temp was 20 degrees.

"Hydroflame" is a name that Atwood uses. Their biggest two-stage 40,000 BTU furnace is 80 watts (6 amps) on low stage and 202 watts (16 amps) on high stage. I had one in a 21 foot Champion motorhome. I suspect anything more then a 20,000 BTU (input) would be overkill in a Toyota motorhome unless you do a lot of arctic camping. They are all pretty inefficient. Most run at 75% tops. That means 25% of the propane is for keeping the birds warm outside.

[zero]

1991 & 1994 Winnebagos had 17,000 BTU, SUBURBAN DD-17DSI, so right around there's about as big as you'll find.

I've found 40,000 BTU furnaces in many big Winnes I've scrapped. 40,000 input and 32,000 of actual heat to the inside. I scrapped one a few months ago with a friend. He took the big 440 Mopar engine and i took the furnace, water tank and a very large 12 volt DC refrigerator.

[zero]

Not sure what's going on. New alternator,regulator,primary battery,coach battery,coach fuse panel,new coach wiring, no shorts.

Just had to order a new furnace control module. The furnace is original,and appears to have upgraded from pilot light to electric.

The mfg. I'd info is missing. Name on thermo is hydro flame. I should mention the two nights I had to use the furnace,the outside temp was 20 degrees.

If you are trying to diagnose ;problems - you need some cheap diagnostic tools. Start at the simple level. Furnace and battery. #1 find out how much power your furnace is actually using. You can buy a digital multimeter from Harbor Freight for $7 and it has a 10 amp scale on it (all you need). Your furnace should probably only draw 6-8 amps max. Then verify what battery you have by AH or RC size AH is amp-hour and RC is reserve capacity. They both tell you the same thing in a different way. A typical Walmart 12 volt type 27 deep cycle battery is rated at 115 AH or 160 RC (approx). Basically good for a steady one amp draw for 115 hours before it's dead. Almost 5 days. Cut that in half or a battery only half-dead and you've got 2 1/2 days. Now - if your furnace draws 8 amps - just divide 2 1/2 days by 8 amps and you get 7 1/2 hours run time. That's with the furnace going non-stop and never shutting off. If running half the time ,that comes to 15 hours of staying warm with one battery. But you need to figure out what battery you have, if it's any good and if it's fully charged before you use. If it does not rise up to near 14 volts when your RV is running, you've got problems.

[zero]

I gave approx numbers in my last post for an RV battery. I just went out and looked at the specs on my newest Walmart type 29 (made by Johnson Controls).

MAXX Marine Maxx-29" "Reserve Cap. Min. : 205, Max Amp Hour rae : 125

That means that . .

With a 205 minute reserve capacity - this battery can power a 25 amp load steady for 205 minutes before it is stone dead (3 1/2 hours). So a 6 amp furnace at 1/4 the draw would run four times as long - i.e. 14 hours by this rating - steady. 7 hours if you only run the battery down half -way.

Using the amp-hour rating - this battery can carry a 1 amp load steady for 125 hours (5 days). So a 6 amp furnace would run steady for 20 hours if the battery was run dead. To half charge - 10 hours.

As you can see the two ratings don't exactly agree - but it's close enough to assume a window of running time.

[fred heath]

Didn't mean to make this a major issue. This is my first foray into any motorhome.

The coach battery is a everlast marine size 24 with 625 marine cranking amps. (new 9/12). The coach battery is receiving 14.32 volts with engine running. Unable to check amp draw until furnace is up and running. (have the tools and know how to use them)

Will keep you posted. Fred

I know the battery is small,but the furnace and 3 led cabin lights are all it,s powering.

[zero]

Didn't mean to make this a major issue. This is my first foray into any motorhome.

The coach battery is a everlast marine size 24 with 625 marine cranking amps. (new 9/12). The coach battery is receiving 14.32 volts with engine running. Unable to check amp draw until furnace is up and running. (have the tools and know how to use them)

Will keep you posted. Fred

I know the battery is small,but the furnace and 3 led cabin lights are all it,s powering.

Cranking amps along with cold cranking amps are pretty useless figures. A typical BCI type 24 sort-of deep cycle battery when to stone dead (10 1/2 - 11 volts) . .

can provide 5 amps for 975 minutes (16 hours).

can provide 10 amps for 402 minutes (6 1/2 hours).

Run the battery to a safe state of 1/2 discharge -

can provide 5 amps for 975 minutes (8 hours).

can provide 10 amps for 402 minutes (3 1/4 hours).

Then if the furnace runs only half time, double the run time.

Your battery is fully charged if after sitting an hour with no charge or load it reads 12.7 volts at room temp.

Your battery is 3/4 charged at 12.4 volts.

Down to 1/2 charge at 12.2 volts (you shouldn't let it get lower).

Stone dead is 11.9 volts.

[fred heath]

Furnace update. New control board installed. Furnace draws 4.15 amps continuous when running.

Did find some suspect ground wires which I replaced. Also found the converter was not producing enough voltage to charge coach battery. New converter on order. The drama continues. Will keep all posted. Fred

[Maineah]

Good deal Fred plugged in a new modern converter should supply all the power you need to keep you warm and your battery charged. The current draw sounds about right this is why without some way to replace the amps they will only make it about 2 days running the furnace on battery.

[zero]

Furnace update. New control board installed. Furnace draws 4.15 amps continuous when running.

Did find some suspect ground wires which I replaced. Also found the converter was not producing enough voltage to charge coach battery. New converter on order. The drama continues. Will keep all posted. Fred

So what did you order? Just curious. Some of the converters are pretty noisy and some are dead silent. No way of telling when ordering by reading specs alone. I'm using a 45 amp Iota and it makes absolutely no noise. You could stick your ear against it and hear nothing. I have various campers with converters that have the battery charge feature, and some without. 30 amp, 20 amp, and 10 amp. All but the Iota make a "vibrating transformer noise" whenever they are on.

[douglitas]

what about using an oversize alternator? could you run the engine in park for a 1/2 hour and charge up the house battery when it got low?

[Maineah]

what about using an oversize alternator? could you run the engine in park for a 1/2 hour and charge up the house battery when it got low?

You can but it's very inefficient. It also over heats the cat because there is no air movement risking the chance of setting fire to stuff your parked over..