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CappyGolucky

Battery upgrade and isolator questions on my '78 Shorty

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 When I bought my 78 micro mini Sunrider last fall the coach battery, a group 27 deep cycle marine, was located under the dinette bench along with  an old power converter the previous owner had installed   The battery was wired and getting juice from the engine battery but wasn't going through the isolator which he showed me was mounted under the hood near the empty battery tray where I assume the coach battery was intended to live.  After doing a bit of research I just picked up a set of 6 V golf cart batteries to upgrade my coach battery capacity.  

Here is what I'm looking to do and I could use some advice from anyone who's got more experience with this stuff than me, which is probably most of you. Lol.  I've now got the 2 6V batteries wired in series under the dinette bench  making one 12 V combo. I'd like to move the marine deep cycle to the tray under the hood and have everything go through the isolator the way it should be  to protect the engine battery . Does this make sense?   What's the best way to wire it up so that I am drawing power from  both the new 12v combo and the marine deep cycle or is it a bad idea having the two batteries far away from each other. 

Also, I haven't come across anything that looks like a power center.  Any ideas where it would be located or even if these early models had a power center would be helpful. Thanks. 

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Your isolator should take care of the issue once you turn off the key the batteries are seperated. You don't want to draw power from the engine battery to supply goodies just to start the truck unless you like walking. Am I understanding that you are replacing the truck battery? Or are you using that also for the coach? What kind of power do you expect to draw from the twin 6 volts? If you have a bunch of batteries you may end up with a charge issue the old alternator was only around 40 amps max. Your pair of 6 volts might top 200 amps plus the deep cycle near 90 then there is always the battery to start the truck.

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 No I didn't want to replace the truck battery. I just got a new one and it's in good shape. what I want  to do is take the old coach battery from under the bench (inside) and install it under the hood.  Then connect that to the isolator which right now I think is being bypassed.  Then I want to connect that one in parallel with the 2  new 6V batteries which are now under the bench.  So the idea is to have a coach battery bank consisting of the deep cycle 12 V battery under the hood and the 2 6V batteries inside the coach,  and have all of those run through the isolator. 

 I just had a new alternator put in which I believe is rated at 30 amps. Now are you saying that this battery setup will be too much for that for the alternator to handle? 

 I intend to do a good amount of dry camping which is why I wanted a decent amount of battery capacity but will only be running a few lights, fans and maybe the radio.  No microwaves or other high power appliances 

 

Edited by CappyGolucky
Addition

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not good to mix n match unlike battery types and ages. the weak shall kill the strong and what you are hoping to achieve may actually ruin the batteries.

the rule of thumb for parallel batteries is same manufacturer, same model and same manufacturing date if possible. They shall be pre-charged and in like condition as much as humanly possible.

 

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Totem is correct is not a real good ideal to mix batteries particularly with different chemistry.  Ok here is the deal your alternator will eventually charge the battery set up you are talking about it will be working overtime at max output and take considerably longer to charge them and they may never reach full capacity unless your on a long trip. I go indefinitely with a 100 watt solar panel and two group 24 batteries the very best thing you can do is reduce your loads get rid of any thing that looks like a light bulb, one incandescent bulb will draw at least 2 amps I have 15 led's in my camper all of them on is only 3 amps.Turn off any thing you can do not to use power. The furnace will suckup a lot of power. I don't know what you are using for batteries but a pair of 6 volts is going to be at least 200 amps you should be able to go for days with just batteries. 

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13 minutes ago, Maineah said:

Totem is correct is not a real good ideal to mix batteries particularly with different chemistry.  Ok here is the deal your alternator will eventually charge the battery set up you are talking about it will be working overtime at max output and take considerably longer to charge them and they may never reach full capacity unless your on a long trip. I go indefinitely with a 100 watt solar panel and two group 24 batteries the very best thing you can do is reduce your loads get rid of any thing that looks like a light bulb, one incandescent bulb will draw at least 2 amps I have 15 led's in my camper all of them on is only 3 amps.Turn off any thing you can do not to use power. The furnace will suckup a lot of power. I don't know what you are using for batteries but a pair of 6 volts is going to be at least 200 amps you should be able to go for days with just batteries. 

X2

Replace your old isolator with this  https://www.amazon.com/Victron-Cyrix-ct-24V-Battery-Combiner/dp/B00ZWLBZME/ref=sr_1_2?ie=UTF8&qid=1511970029&sr=8-2&keywords=battery+combiner

Add a simple 100w solar kit  https://www.ebay.com/itm/PV-SOLAR-KIT-100-W-Watt-100Watts-PV-Solar-Panel-12V-RV-Boat-Charge-Controller/172307351275?hash=item281e5186eb:g:fQkAAOSwgZ1XseVy

Do this and your house batteries ( 2-6v batteries) and truck battery will be forever charged

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15 hours ago, Totem said:

not good to mix n match unlike battery types and ages. the weak shall kill the strong and what you are hoping to achieve may actually ruin the batteries.

the rule of thumb for parallel batteries is same manufacturer, same model and same manufacturing date if possible. They shall be pre-charged and in like condition as much as humanly possible.

 

Yes I have heard conflicting views about this.  Some say it applies more to wiring batteries in series than in parallel but still probably not the best idea.  Here's one of the more persuasive descriptions I've seen 

https://www.homepower.com/articles/solar-electricity/design-installation/ask-experts-batteries-series-parallel

So from the advice I'm getting here it sounds like maybe I should scrap the idea of mounting the old marine 12v under the hood and just go with the 2 6v wired in series in the coach.  Then take WME's advice and get a new "smarter" isolator to connect between the coach and engine batts.  

I definitely had in mind as a future project mounting a couple solar panels up top (maybe 200w).  Pretty sure that would keep us well supplied with power given the kind of low power devices/appliances we'll be running.  Btw I've already got all the incandescent bulbs swapped out for LED's and have plumbed and mounted an Olympian Wave 3 catalytic propane heater which requires no electric for fans.  So I'm definitely of the same mind when it comes to reducing draw.  

 

 

 

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8 hours ago, WME said:

So I think what's in there now is some type of a solenoid dual battery isolator.  Looks to be a old as the truck and I'm seriously doubtful if it works.  Probably why one of the previous owners decided to bypass it.  So in your opinion what are the benefits of the battery combiner over the isolator?  Is it because the charge can go both ways?  Also, if I understand it this will effectively combine the two 6v coach batteries in parallel with the engine battery but in a way that negates the problem of them being different type/capacity?  Is that right?

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A new solenoid isolator will do what you need, the combiner/isolator is gold plating the answer. It measures the voltage of each 12v "battery" separately and keeps things balanced Whats your pocketbook think?

Unless you have a large active load a 100w panel will be enough as you don't a high draw heater in use.

What ever you do rewire the electrical battery system with continuous runs of 6 or 8 gauge wire to everything. Who knows has been done to the rig in the past 40 years

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So if you add a second coach battery, the combiner/isolater on Amazon would replace the isolator below, or be in addition to the isolator below?

IMG_20171124_101310839.jpg

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8 hours ago, WME said:

A new solenoid isolator will do what you need, the combiner/isolator is gold plating the answer. It measures the voltage of each 12v "battery" separately and keeps things balanced Whats your pocketbook think?

Price sounds good to me. Not much more than a standard solenoid relay unit from what I’m seeing and definitely worth the peace of mind. 

So I have one more concern and that’s about the sound system. Believe it or not all the truck came with was an old CB radio so I’m having a new stereo installed in the cab. I was thinking it would be smart to have it connected to the coach battery bank for use during dry camping but now I’m wondering if that will be necessary. If I were to use the battery connector suggested would that hypothetically  keep the truck battery charging from the coach battery bank (or the solar panels)  if the stereo was drawing power from it while not running the engine? 

Edited by CappyGolucky

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Why do you think you need two isolators? The ideal is to keep your truck battery from discharging, the one you have does that. A combiner will connect the batteries by voltage but you will have to chose the bank that needs to be "protected" usually that's the truck battery for more than one reason one you don't want that one to go flat and second it is connected to the alternator output. The combiners being "smart" allows the truck battery to charge first so if the coach is  primary it will be the one that runs the show and when it's charge is higher it will attempt to charge the truck battery thus draining the coach battery because it has no way to recharge. Combiners can be hooked either way they don't care so it is important that the truck battery side is just that. The radio is pretty low current I don't believe I would over think that. The bottom line you should concentrate on isolating the truck battery from the coach. A simple pair of jumper cables would get you started from the coach batteries in a bind. If you  are adding solar again that would be for the coach no need to charge truck battery if it's just sitting there doing nothing. 

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I think you need to check things out from the beginning. Verify each part is working or not. Just throwing parts at a simple problem is not the way to go.

Get a simple cheap Harbor Freight VOM, it will become your new BFF

Looking at your picture I see the isolator and what appears to be an inline auto reset breaker. The breaker looks toasty.

Check the isolator...https://www.youtube.com/watch?v=oqCUyJ2P3yI

 

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58 minutes ago, WME said:

I think you need to check things out from the beginning. Verify each part is working or not. Just throwing parts at a simple problem is not the way to go.

Get a simple cheap Harbor Freight VOM, it will become your new BFF

Looking at your picture I see the isolator and what appears to be an inline auto reset breaker. The breaker looks toasty.

Check the isolator...https://www.youtube.com/watch?v=oqCUyJ2P3yI

 

Yeah WME  that post with the photo wasn't mine.  Someone else jumping in I guess.  I'm leaning towards going with the battery connector you recommended and maybe this spring or summer investing in a 100w solar kit for starters.  Thanks for the help all. 

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OOPs need to read more carefully,, Anyway advice still stands get volt meter and rewire battery charge system

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On 2/6/2018 at 9:51 PM, WME said:

A new solenoid isolator will do what you need, the combiner/isolator is gold plating the answer. It measures the voltage of each 12v "battery" separately and keeps things balanced Whats your pocketbook think?

Unless you have a large active load a 100w panel will be enough as you don't a high draw heater in use.

What ever you do rewire the electrical battery system with continuous runs of 6 or 8 gauge wire to everything. Who knows has been done to the rig in the past 40 years

 WME I took your advice and got one of those battery combiners off Amazon. Now I'm  just trying to figure out the best way to set it up. Originally I had planned to locate it in the coach near the house batteries but  instructions say to put it close to the engine battery. What's your take? Is it best to keep it placed where the old isolator was  under the hood? 

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10 minutes ago, CappyGolucky said:

 WME I took your advice and got one of those battery combiners off Amazon. Now I'm  just trying to figure out the best way to set it up. Originally I had planned to locate it in the coach near the house batteries but  instructions say to put it close to the engine battery. What's your take? Is it best to keep it placed where the old isolator was  under the hood? 

It's the simplest and will work fine. Once you have it read the theory of operation that will explain a lot.  

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Because of the way the combiner works it needs to be close to the truck battery. The combiner gets power from the truck battery not the alternator.

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It will work at the coach batteries but it needs to be connected properly otherwise you run the risk of a dead truck battery it can be connected backwards. Another problem you will run into is the .7 volt voltage drop through the solid state isolator the combiner is dependent on voltage entirely. You would be far better off to remove solid state isolator and replace it with the combiner this will require a bit of rewiring because the B+ from the alternator no longer is connected to the battery and it will have to be reconnected to the truck battery B+.

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28 minutes ago, Maineah said:

It will work at the coach batteries but it needs to be connected properly otherwise you run the risk of a dead truck battery it can be connected backwards. Another problem you will run into is the .7 volt voltage drop through the solid state isolator the combiner is dependent on voltage entirely. You would be far better off to remove solid state isolator and replace it with the combiner this will require a bit of rewiring because the B+ from the alternator no longer is connected to the battery and it will have to be reconnected to the truck battery B+.

Yeah  that was my intention to replace the old solenoid relay with the combiner. But from what you're saying it sounds like they are wired completely differently .  I'll have to get under the hood and check it out but  i'm pretty sure the existing isolator is being bypassed right now so the truck battery is directly connected to the coach batteries with no protection. 

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Checking some wire size calculators, You need 4 gauge wire from the alternator to the truck battery and from the battery to the combiner. And 2 gauge from the combiner to the house batteries. Probably 4 or 6 gauge from the batteries to the power panel. This are large wires, think cheap jumper cables.  These numbers are based on a 1% power loss and 45 amps

So try  welding supply or a large auto parts store. If you don't have a VERY good crimper, lay every thing out, cut the wire to proper length and go back to where you bought the cable and have them crimp on good  terminals. Protect each connection with an anti-corrosive something

Some will say these is overkill for an isolator and they would be right, but the combiner works differently and is voltage sensitive.

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5 hours ago, CappyGolucky said:

Yeah  that was my intention to replace the old solenoid relay with the combiner. But from what you're saying it sounds like they are wired completely differently .  I'll have to get under the hood and check it out but  i'm pretty sure the existing isolator is being bypassed right now so the truck battery is directly connected to the coach batteries with no protection. 

 I was looking at the picture you posted, if it has a relay type isolator then it is a direct replacement. The small relay wire will no longer be used so that will have to be removed or protected because it will be hot with the key on. I'm still confused as to what you a trying to accomplish if the picture you posted is what you have it is not a relay isolator and will require a bit of wiring to make the combiner work. The solid state isolator has 3 or in your case with a "91" MH 4 wires two battery wires one alternator wire and an exciter wire. The truck battery wire will have to be joined to the alternator wire or it won't charge either battery. Here is the deal years ago (and even to this day) the coach wire was only a # 8 or at best a # 6 wire this was fine for low demand use but as WRE said if you want max smoke you need to upgrade the wire. It boils down to how much power do you really need? With the stock wiring and a couple hundred amp batteries the small wire will take a long time to charge your batteries, lots of miles of driving. If you are going to use solar you need to figure out just how much power you are going to use and just how much power the panel can provide on any given day if they don't equal out the batteries will not be charged. A simple fix would be a generator and a good converter/charger if you want a lot of current.

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22 hours ago, Maineah said:

 I was looking at the picture you posted, if it has a relay type isolator then it is a direct replacement. The small relay wire will no longer be used so that will have to be removed or protected because it will be hot with the key on. I'm still confused as to what you a trying to accomplish if the picture you posted is what you have it is not a relay isolator and will require a bit of wiring to make the combiner work. The solid state isolator has 3 or in your case with a "91" MH 4 wires two battery wires one alternator wire and an exciter wire. The truck battery wire will have to be joined to the alternator wire or it won't charge either battery. Here is the deal years ago (and even to this day) the coach wire was only a # 8 or at best a # 6 wire this was fine for low demand use but as WRE said if you want max smoke you need to upgrade the wire. It boils down to how much power do you really need? With the stock wiring and a couple hundred amp batteries the small wire will take a long time to charge your batteries, lots of miles of driving. If you are going to use solar you need to figure out just how much power you are going to use and just how much power the panel can provide on any given day if they don't equal out the batteries will not be charged. A simple fix would be a generator and a good converter/charger if you want a lot of current.

Actually that wasn’t my pic. Sorry for the confusion but it looks like someone else jumped into the thread. Haven’t been able to post pics from my iPad but what I have is a very old and worn lookin solenoid relay which has been disconnected and bypassed. 

Youre correct however about the wire. Looks like about only 10 or even 12awg. I agree with u about upgrading it. This job is getting a little more complicated than I was hoping and I’m not big on messing around with electrical systems. May need to bring it in and get some help with it. Unfortunately there aren’t many RV techs in my area. May try a car audio  shop. I know they work with dual batt systems some. Thanks for the help. 

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Ya car stereo guys deal with big wire, so do off road folks with their wenches.

 

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