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Old 07-17-2012, 07:40 PM   #1
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House battery help

So, I installed another battery in the van with a blue sea isolator. The battery is a marine battery but I don't think it's getting a good charge from the alt and if i put a battery tender on the starter battery side the isolator wont show that its charging the house battery too. I have a 3500 watt inverter to run a norcold fridge and now a portable ac that pulls 950watts. It runs for about 5min and the inverter starts setting off its alarm. I'm guessing the battery is not enough?
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Old 07-17-2012, 09:33 PM   #2
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Re: House battery help

Pretty sure my battery is wayyyy to small... I've determined I have about 1150 watts pulling a small marine battery. Damnit. Got some serious work to do now.
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Old 07-18-2012, 09:46 PM   #3
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Re: House battery help

Read up on the FAQ's at the upper portion of this section.

There is no way that even 3 marine batteries will run your AC too long without help from shore power. 3500 watt inverter itself probably pulls around 3-5 amps just in the on position when feeding nothing. Your refrigerator should be running off the house battery not your inverter provided you have a 2-way fridge.

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Old 07-18-2012, 10:08 PM   #4
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Re: House battery help

Yes, and you could also have things wired wrong. For instance, I found out the hard way that an inverter negative HAS to be wired straight from the battery negative, NOT to straight to ground. Also, how big and how long are your wires from batteries to inverter? Shouldn't be more than a couple of feet.
Dave is right though, you won't run ANY air conditioner for long without a generator or shore power, or any microwave, electric heater or anything like that.
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Old 07-19-2012, 08:44 AM   #5
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Re: House battery help

OK. Well, I know the battery is just not enough. The inverter is wired directly to the house battery with 2 positives and 2 negatives (both 4ga.)...that's what the inverter came with. The norcold only came with 110ac cord so it runs off the inverter. Only thing running off starter is what normally would but its tired to the isolator just in case I need a boost to start.
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Old 07-19-2012, 10:19 AM   #6
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Re: House battery help

Are you sure the fridge is AC only? I doubt that. You'll be way ahead if it can be run off the house DC. If you have to convert the DC to AC to run the fridge, you will be pulling around 3-5 amps continuous to operate the inverter and probably about an additional 2-3 amps to run the fridge when it cycles on. You will need close to twin 4-D 220AH batteries to keep the house system from dipping below 50% of state of charge using your setup as it is during an overnight session. I think you should read this Link maybe it will help. The AC/DC refrigerators automatically switch over to AC when they detect it and is why the AC breaker should be opened (turned off) when using the inverter while off shore power. When hooked up to shore power (even while sitting at home) the unit draws from the AC outlets and the inverter doesn't need to be turned on. Most inverters will pass the shore power through the inverter directly to the outlets without the need to be activated.
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Old 07-19-2012, 11:36 AM   #7
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Re: House battery help

Quote:
Originally Posted by racrx451
So, I installed another battery in the van with a blue sea isolator. The battery is a marine battery but I don't think it's getting a good charge from the alt and if i put a battery tender on the starter battery side the isolator wont show that its charging the house battery too. I have a 3500 watt inverter to run a norcold fridge and now a portable ac that pulls 950watts. It runs for about 5min and the inverter starts setting off its alarm. I'm guessing the battery is not enough?
Lets start here. If you hook up your battery tender to the main battery it should NOT charge the house battery. If you want to charge both batteries you need to hook it to the center/altenator post. An isolator blocks the direction of charge thats how it isolates. You also mentioned something about jump starting with your isolator. Unless you used really large wire size and have some special isolator you cant really use it for jump starting. Maybe it would help us advise you better if we had the model numbers (or links) of your isolator, battery, battery tender, inverter and even your fidge.

First you really need a voltmeter or something to make sure its charging both batteries and their state of charge. You really need to monitor this to get the best use out of your battery. You need to understand how long it takes to fully charge a battery and what the different voltage means to the batteries state of chage. Next I think you need to research how all of this stuff works. Use daveb's link, the people like him on this forum know a lot about this stuff.

If your fridge is really 110 volt only its not the best one for your van, maybe you could sell it and get a 12volt one. Using the inverter to make 110 volts takes extra power for the conversion. No matter how big your battery is it wont last long using the inverter all the time to run your fridge. As for what daveb said about "Most inverters will pass the shore power through the inverter directly to the outlets without the need to be activated." he means if your inverter has a built in shore power charger. Since you mentioned using a battery tender my guess is you have a inverter only without a built in charger. Also a battery tender can take days to fully charge a battery keep, that in mind.

I think once you understand a bit more how it all works you will understand why an A/C unit will never work no matter what.
But you might be able to use the battery you have with a 12volt fridge for a few days without starting the van, it all depends on your needs.
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Old 07-19-2012, 12:59 PM   #8
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Re: House battery help

Yep I missed that the term "isolator" was used instead of "separator" even though they provide a similar function.
racrx451 technically Isolators are usually fully solid state units and separators usually incorporate a relay or mechanical latch of some sort that open up a set of contacts. Separators still use electronics to monitor voltages to know when they need to open up and close. Some separators are uni-directional (allow current to flow one direction) and some are bi-directional (current can flow in two directions).
Everything Ultrasport12 posted is correct and really you do need to post what you are actually using to get a better solution for your issue.

Most of the inverters SMB install on thier production line are Inverter/chargers. Many generic type inverters are simple units that just attach to a battery system and only have an on/off switch to convert the DC power to AC. Those generally do not interface with the shore power electrical system other than the user supplying a cord from the AC output of the inverter to a outlet inside the van. Many owners don't even hook to an "in van" outlet and just use the outlet(S) provided on the inverter itself. In those types of builds its common for the owner to request or install a AC to DC "converter/charger" to charge the house battery and supply 12vDC while on shore power.
With a battery "tender" hooked to the starting battery, Ultrasport is correct, the isolator will only allow the charge to apply to the starting battery if hooked up correctly. Being they only allow current to flow in one direction, you'll never get a charge from the battery tender or alternator to the house. You could flip it around but then you'll run the risk of killing both battery systems when using the house battery which defeats having the isolator in the first place. On the other hand, if you actually have a bi directional Blue Sea "Separator" like I think you might have, it should allow the alternator to charge the house battery. Below is a page from Blue Sea about their products. Greg also did a great post on a variety of configurations:
viewtopic.php?f=14&t=8842

There are other possibilities but these are the usual methods most use which is a reason why you really need to post what equipment you have.


Battery Isolators and Automatic Charging Relays
Battery Isolators, Automatic Charging Relays (also called ACRs , combiners, or voltage sensitive relays) are all intended to keep a load (or loads) from discharging the reserve battery system. The reserve battery system is used for vital loads like engine starting, navigation or communications. Battery Isolators and ACRs are intended to distribute current from a charging source to all batteries, but leave the batteries isolated during discharge conditions so they are only impacted by their own loads.

Battery Isolators are made with two or more silicon diodes that act like check valves. The diodes will pass current from the charging source to the batteries, but will not pass current backward from one battery to the other or back to the charging source. Nature extracts a price for this by causing a voltage drop of about 0.7 Volts across the diodes. If you have a regulated charging source that senses its own output, the voltage at the battery will be lower than at the charger or regulator and, if not compensated for, will lead to inadequate charging.

ACRs or Automatic Charging Relays are automatic switches that close when the voltage on one of the batteries rises to a level (normally 13.2V to 13.7V) indicating the battery is connected to a charge source and is partially or fully charged. The switch then closes and shares the charging current with the other battery until the voltage drops to some lower level (normally 12.4 to 13.1 depending on model) and the switch opens. This prevents discharging both batteries when there is not enough current to charge both batteries.

With the ACR or an isolator, the batteries are effectively connected together during charging and disconnected during discharge. The isolator is the simpler of the two approaches, when used with remote sensing chargers and regulators, but without remote sensing the isolator gives poor performance.

The ACR simplifies the system design because chargers and regulators that work with a single battery bank will still work with a multiple battery bank. Outboard motors and inverter / chargers have a single line that provides charge current, but can also absorb starting current or inverter current. They can't be connected through an isolator because the isolator will not permit the backward flow of energy when the source becomes an intended load.

There is an issue with multi-stage chargers which cut back to a lower charging voltage for “float“. If the charger is supplying one lightly loaded battery directly and supplying a second battery through an ACR, and the second battery is the one that gets loaded, the system may not respond. The voltage of the first battery can be too low to trigger the ACR during the float stage while the loaded battery is being discharged. Because the ACR does not close, the multi-stage charger cannot see that the second battery needs charging current. This is usually resolved by connecting the multi-stage charger to the battery that has a load connected instead of connecting to the unloaded bank. Many multi-stage chargers also come with multiple outputs and the second output can be helpful in this situation and avoid loss of charge during the float stage.

ACRs and Battery Isolators are a valuable addition to a battery management system and simplify charging multiple battery banks while protecting the reserve battery system. Below is a diagram of an ACR used in a two battery system.

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Old 07-19-2012, 03:08 PM   #9
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Re: House battery help

Just FYI, like Dave and Ultrasport, many folks told me I wouldn't be able to run an AC fridge very well with deep cell batteries, but I have been doing it for over a year with no problems. Using an isolator from my van battery, tied to 2 Walmart (Johnson Controls) 105 amp/hour batteries, through a 1500 watt Tripp-Lite inverter/charger, I can go just fine for about 24 hours if fully charged before I drop to 12 volts. Humidity and heat do matter of course, since the fridge will cycle on a lot more. I have a big GE dorm fridge and a couple of small things like phone chargers running on this system always, as well as some additional lighting I've tied in to the house batteries. When it's not really hot, I can go about 2 days before I'm down to 12 volts.
It can be done, but you have to be careful with your charging/voltage or you will kill your batteries.

Also, even though this works OK, I'm hoping for a true DC Truckfridge in the next year or so, which I believe would make the system much more durable.
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Old 07-19-2012, 04:31 PM   #10
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Re: House battery help

Quote:
Originally Posted by 86Scotty
Just FYI, like Dave and Ultrasport, many folks told me I wouldn't be able to run an AC fridge very well with deep cell batteries, but I have been doing it for over a year with no problems. Using an isolator from my van battery, tied to 2 Walmart (Johnson Controls) 105 amp/hour batteries, through a 1500 watt Tripp-Lite inverter/charger, I can go just fine for about 24 hours if fully charged before I drop to 12 volts. Humidity and heat do matter of course, since the fridge will cycle on a lot more. I have a big GE dorm fridge and a couple of small things like phone chargers running on this system always, as well as some additional lighting I've tied in to the house batteries. When it's not really hot, I can go about 2 days before I'm down to 12 volts.
It can be done, but you have to be careful with your charging/voltage or you will kill your batteries.

Also, even though this works OK, I'm hoping for a true DC Truckfridge in the next year or so, which I believe would make the system much more durable.
I think it depends on both the draw from the fridge and the size of the inverter. A 3500 watt inverter is pretty large, and some units are not as efficiant. Testing amperage would be key. I'm not saying it can't be done, it's just gonna put a toll on smaller house batteries. I'm running the larger 4cf fridge and it pulls around 3 amps when it cycles on. My 2000 watt Xantrex inverter pulls about 3 amps while sitting idle in the on position. If I add the load of the refrigerator to the inverter, it pulls slightly more than it does off the DC only mode. To keep a single 4-D battery above 50% (12.2v) it just doesn't leave room for much else. My stereo system, lighting, and heater also suck down my battery system at night and at least in my situation my battery (when I had a single battery) was pushing the limit by morning. Each person needs to calculate what their loads will be.
Another solution besides swapping the AC fridge for an AC/DC model would be to install a smaller inverter that is speced for the fridge only and use it instead of cranking up the big boy.
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