Replacing Battery Isolator with Voltage Sensing Relay

[Stevemo]

Every time I look under the hood of my van I spot the battery isolator. It's giant and you lose 0.7 Volts because of the diodes. Has anybody removed one and installed a voltage sensing relay? This is on a 2004 Roadtrek Chevy Express 3500 Popular 190 complete with 145 amp alternator.

Background information (information overload...):

Alternator wiring:

https://www.hemmings.com/blog/article/delco-cs130-alternators/

https://www.motor.com/wp-content/uploads/DiagnosingComputerControlledChargingSystems-September2007.pdf

• P, output to accessories such tach or hour meter (not used)
• L, alternator dummy light and excitation (brown wire)
• F, external field monitor (not used)
• S, battery voltage sensing wire (to battery + terminal or very close to battery+ terminal)
• Stud, alternator output to battery

Here's the isolator I have:

Battery Isolator 90 amp 1 alternator 2 batteries w/reg terminal - e Marine Systems

- #ISH33013-C Battery Isolator 90 amp 1 alternator 2 batteries w/reg terminal

www.emarineinc.com

http://www.texasindustrialelectric.com/pdf/33_21_Isolator_wiring.pdf (Page 9)

• B1
  • main battery +
  • S terminal on alternator
• B2
  • coach battery +
• E
  • key on relay circuit, E is fed from battery when key on
• A
  • Alternator output

The voltage sensing relays are really simple. There is just an in and an out with a rating of 125 to 140 amps.

http://assets.bluesea.com/files/resources/instructions/990170140.pdf

I am thinking of hooking it up like this:

• In
  • main battery +
  • alternator output
  • alternator S terminal
• Out
  • coach battery +

I had one of these relays in my 1991 Roadtrek which had simpler wiring. The one drawback with the voltage sensing relay is that you need to install big wire and self-resetting breakers because there is no current regulation. I initially had manual reset 80 amp breakers and they would trip every time I pressed the gas pedal when the coach battery was low. The 145 amp alternator is calling for a #1 wire and 175 amp breakers to prevent tripping according to Blue Sea.

 

[Bikersmurf]

Easy to do. I found the starting batteries needed to be connected to the alternator and the house batteries to the other terminal. I’ve not added new resettable breakers but they would be a good idea. The ‘original’ Ambulance wiring is 1 or larger wiring.

Given the alternator can put out 210 amps continually and I’ve read even higher when cold, I’m inclined to leave it wired as Crestline wired it and not search out 220A or similar breakers.

 

[Bikersmurf]

I have found that the ACR doesn’t like to charge the house batteries if the voltage differential is too great. In those instances I’ve hit a manual switch to temporarily jump the house batteries to the starting batteries. I’ve only needed to do this a couple times for a few seconds, but I’m sure it’s not great for the batteries. I’ve not needed to jump them after converting to a pair of 6V Golf Cart batteries.

There’s a night and day difference between GC batteries and Marine Deep Cycle batteries (which are crap in comparison).

 

[Corneilius]

What differences have you notice between the 6v and the 12v marine? Generally happier with them? Were your 12v batteries at the end of their life?

 

[luthj]

There are very few true deep cycle batteries sold in big box stores, and even less with the "marine" tag. Comparing those 12V marine or dual purpose "deep cycle" batteries to a true industrial deep cycle (such as the trojan, deka, duracell GC2 offering) is a stark comparison.

 

[Stevemo]

Bikesmurf: Which VSR are you using? It seems that you've got quite a bit more current passing through it than I've seen available. This may be handy if I put in a 2nd alternator or swap the one I've got with a 300 amp job.

The 6 Volt batteries and a good charger are a whole other story. My other van had two Trojan T-105 Plus batteries, a 25/50 amp charger, and a 2000 watt pure sine wave inverter. I never lacked power with that system except when I let it get too low and wasn't able to charge it with the alternator (tripped breaker issue). Those batteries were happy to suck up all the power the alternator could put out. I ended up removing the original 6 amp battery charger the DC panel had built into it because it would take too long to restore the batteries and it did not have any intelligence. You really need to pick a charger that has at least 3 stages, has a battery temperature sensor, adjusts voltage based on technology, and is quiet. Be careful when you set the final stage voltage if you draw power from the batteries at the same time as you charge them. That is a recipe for boiled batteries if not programmed properly.

I have a 2.8 kW generator under the new van which weighs about 130 pounds installed. I would probably be happier with a big alternator, 3000 watt pure sine wave inverter, and four 6 Volt batteries. The weight would be the same and I could run the engine for a bit if I needed power to run the AC.

 

[scottrinne]

I’m by no means an expert, but I have been doing a little research on this for my van project.

I will be using a diod isolator. Yes, its more expensive and slightly lowers the charging voltage, but the benefits out weigh those drawbacks:
1.) no mechanic failure point like in the voltage sending relay
2.) It never parallel jumps the two batteries together. (Each battery has different requirements one can’t drain the other)
3.) suppose to last longer

 

[Toyaddict]

I've been running one of these for 1 1/2 years in my van with no issues as of now. My usage is slightly different as I only have 1 75ah house battery. I have a 100A breaker in line and it has yet to trip but that may change when I add a second house battery.

I really like that both house and starting battery are charged off my solar when the van sits unused. I have the solar charger set to AGM for the house battery but starting is flooded cell, makes me wonder if that charging logic damages the starting battery.
JayCorp Smart Dual Battery 140A Isolator (VSR Voltage Sensitive Relay) for Auto/Boat/RV https://www.amazon.com/dp/B00400IYTK/ref=cm_sw_r_cp_api_i_Dv5CDb5K7M3VV

 

[luthj]

Diode isolators can fail.

Due to their voltage drop they have minimal value for charging batteries. When charging lead acid the 0.2-0.4V drop of an diode isolaor will decimate charge rates.

There are a tiny fraction of cases where a diode isolator would be preferred, for every other case a quality relay will work much better. This can be a VSR style, or just an ignition/D+ triggered relay.

 

[WVI]

Toyaddict, that's the one I was thinking about trying.

 

[shade]

Here's a good price on a Blue Sea 7610 ACR from a reputable, knowledgeable seller.

https://shop.marinehowto.com/products/blue-sea-7610-automatic-combining-relay

 

[Stevemo]

I installed one like that in my Dodge. I went with the dual sensing version so that it would close when the alternator was charging and when the battery charger was charging. The single sense models only close on one of the two so keep that in mind.

 

[shade]

Here's a great article on Automatic Charging Relays.

Blue Sea Systems has several options, and provides a guide for selecting the best one for your application. I'm sure someone has had a bad experience with one, but I haven't read about it yet. If I wasn't planning a system around Victron components, I'd likely have a Blue Sea ACR under the hood.

 

[Bikersmurf]

Bikesmurf: Which VSR are you using? It seems that you've got quite a bit more current passing through it than I've seen available. This may be handy if I put in a 2nd alternator or swap the one I've got with a 300 amp job.

The 6 Volt batteries and a good charger are a whole other story. My other van had two Trojan T-105 Plus batteries, a 25/50 amp charger, and a 2000 watt pure sine wave inverter. I never lacked power with that system except when I let it get too low and wasn't able to charge it with the alternator (tripped breaker issue). Those batteries were happy to suck up all the power the alternator could put out. I ended up removing the original 6 amp battery charger the DC panel had built into it because it would take too long to restore the batteries and it did not have any intelligence. You really need to pick a charger that has at least 3 stages, has a battery temperature sensor, adjusts voltage based on technology, and is quiet. Be careful when you set the final stage voltage if you draw power from the batteries at the same time as you charge them. That is a recipe for boiled batteries if not programmed properly.

I have a 2.8 kW generator under the new van which weighs about 130 pounds installed. I would probably be happier with a big alternator, 3000 watt pure sine wave inverter, and four 6 Volt batteries. The weight would be the same and I could run the engine for a bit if I needed power to run the AC.

I’m using a Blue Sea 7610... I believe. It’s rated to handle 215 amps for 5 minutes. The house batteries usually only draw about 100 amps peak. Any time the alternator is pushing more than 120 amps, a large chunk of it is recharging the starting batteries (which doesn’t go through the relay).

I’d planned on wiring the alternator to the house batteries, but I found the alternator output feedback is through the OEM wiring to the starting batteries. Alternator output was peaking at about 15.2 v until the ACR connected the banks... this was knocking out the inverter which has an input limit of 15 v. With the alternator wired to the starting bank, that problem went away. I could dig deeper into the alternator wiring to solve this, but I’m taking the path of least resistance for now.

To buy an ACR over, I’d get the Blue Sea 7620 rated for 500 A output.

If I decide to use the rig as a generator I’ll just add a switch to keep the sure start relays closed... or a manual battery switch to connect the banks.

Re 6V x 2:
1) the pair of 12v marine couldn’t last 24 hours running the fridge.
2) the two 6V ran the fridge for 3 days after I’d drained them to 12.3v.
3) the 12v wouldn’t run the microwave for more than 2 minutes or handle the starting load of my smallest 120v compressor.
4) the 6V have no problem with running the microwave for longer (even when already drained) and can also run the compressor fine.

I’m running a TRUECHARGE 20 multistage charger to keep them all in top shape when connected to shore power. Also a solar panel with multi stage change controller for times not connected to shore power.

 

[WVI]

Thanks for the info links Shade