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Topic: Dual alternator setup - remove diode isolator? (Read 465 times) previous topic - next topic
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Dual alternator setup - remove diode isolator?
I'm just starting a major electrical upgrade on the new-to-us 2002 MB. I'll be documenting that entire process in another thread, but am in the planning stages with some of the components. This is my fourth Victron/lithium install, having worked with AM Solar on all of them - so I've got a pretty decent understanding of the process. Every install throws a couple curve balls though, and this one is no exception.

None of my previous installations have been in motorhomes - just travel trailers and a cargo van. As such, this is the first where I've encountered a diode isolator. And, it's also the first where I'll be incorporating a new dual alternator setup. A 280A alternator/bracket and Wakespeed 500 controller is on the way which will handle bulk charging of the 600AH lithium bank.

If my research is correct, the diode isolator is only in place to address current flow when the single alternator is charging both house and coach batteries. Correct? If so, would I be correct in assuming it is no longer needed in a dual alternator setup? The stock alternator will be charging the engine battery, the high output 280A will only be hooked up to the house bank. I'll be upgrading the current 6g that runs from the diode isolator to the old battery bank with 4/0 as significantly more charging current will now be possible.

I do see from the attached factory wiring diagram that a couple accessories are connected to the diode isolator, but it would seem these could easily be connected to another 12v source in the coach.

I know a couple of you have gone down this path before. Any feedback appreciated!

Will
2002 26.5 MB

Previous: 2011 27 RB, 2005 24 TK
Re: Dual alternator setup - remove diode isolator?
Reply #1 –
The diode isolator is no longer needed. All the chassis connections to the isolator can go directly to the alternator output, and the rest to the second alternator. BUT... the diodes in the isolator had a 0.5V to 1.5V voltage drop depending on the current through them. This means they dissipated quite a bit of energy as heat. Wasted energy, but it also acted as a current limiter for the alternator output. If the Wakespeed 500 performs a similar protective function in your setup, then you are set.

Steve
2004 FL
2013 Honda Fit
Re: Dual alternator setup - remove diode isolator?
Reply #2 –
I removed the isolator in my install and am using a DC to DC charger instead. The isolator wouldn't serve any purpose in your setup in that you will have separate charging sources.

I can hardly wait to read about your project. I never heard of anyone doing a 2-alternator solution. Lots of amperage and that 4/0 will handle it easily. Hard to deal with though and nowadays really expensive.
jor
09 27' MB
10  Suby Forester
Re: Dual alternator setup - remove diode isolator?
Reply #3 –
Hi Will; The purpose of the diode isolator is to isolate the chassis battery from the house batteries when the alternator isn't producing power. Engine not running. That is so you can run down the house battery and still be able to start the car engine.
  Because the chassis battery is still lead acid (chassis engine heat/cold as Larry pointed out), it needs different treatment than the Lithium bats. Like Jor, I  used a DC to DC converter to change up the voltage from the alternator to the higher voltage needed for LiF batteries.
   With a second alternator ypu have an advantage isolating the batteries. You might still want to use a relay to connect the LiF to start the engine, if the chassis battery has an issue.  RonB
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Dual alternator setup - remove diode isolator?
Reply #4 –
Quote from: jor  - 
I removed the isolator in my install and am using a DC to DC charger instead. The isolator wouldn't serve any purpose in your setup in that you will have separate charging sources.

I can hardly wait to read about your project. I never heard of anyone doing a 2-alternator solution.

The isolators were only rated at 70-100 amps, they would quickly fail with over 200 amps flowing through it. The stock wiring would burn.

This isn't the first upgrade on the Forum to use this alternator kit. Craig P. used the same two years ago while building an office on wheels. It looks like a very tight installation.
Alternator Upgrade

The new Ford V8 has an optional second 250-amp alternator, the V10 never had a Factory second alternator option but there is room for for more powerful alternators. With lithium battery's ability to charge efficiently at high current rates, this is a good way to quickly charge large battery banks.
If I were doing this, a single high-output alternator would be used to charge the large lithium bank and a big DC-DC charger would keep the starting battery charged.
High-output replacement alternators are available from 250 to 400 amps. It would be a lot simpler and cheaper than adding a second alternator.
2003 Ford E-350 Super Duty 6.8L V10 415CID High Output Alternators | Tucson...

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Dual alternator setup - remove diode isolator?
Reply #5 –
Quote from: Larry W  - 
This isn't the first upgrade on the Forum to use this alternator kit. Craig P. used the same two years ago while building an office on wheels.

Yep, that's where I first read about it. Craig was most helpful in answering questions, and also shared thoughts and experiences that convinced me a single, high output alternator was not the path I wanted to go down.

Quote from: Larry W  - 
If I were doing this, a single high-output alternator would be used to charge the large lithium bank and a big DC-DC charger would keep the starting battery charged.
High-output replacement alternators are available from 250 to 400 amps. It would be a lot simpler and cheaper than adding a second alternator.

Well, Larry - I usually find your advice spot on, and perhaps I'm missing something here. However, that doesn't sound significantly less complicated and adds risk I'd rather not have.

Compared to dual alternators, it introduces three single points of failure on the engine charging side of things, any of which could leave us stranded. First there's the single alternator, which is now heavily taxed performing both engine and house duties on a significantly larger battery bank. Second, the DC-DC charger is now needed to keep the engine battery topped off - not needed with dual alternators. Lastly, even for a larger single alternator directly charging a large and expensive lithium bank, I'd not want that setup without an external regulator like the Wakespeed to properly and safely deliver proper voltage and current to the house side of things. I'm sure you're aware of the risks of expensive damage that can be caused by rapid BMS disconnects on lithiums, and smart, external regulators like the Wakespeed reduce that risk significantly.

The larger single alternator system would cost less, but with the addition of the DC-DC charger and Wakespeed the difference is not huge - to us, anyway. It also requires more space in the already limited area we plan on installing components under the fridge.

A big part of the reason we searched out an older, well cared for LD was the significant price savings over a newer model. We're putting those savings to work by not cutting any corners on upgrades, and performing plenty of them. So, for us - the more robust and fault tolerant dual alternator setup is worth the added expense, easily covered by the many tens of thousands of $$ we saved over buying a newer coach.
2002 26.5 MB

Previous: 2011 27 RB, 2005 24 TK
Re: Dual alternator setup - remove diode isolator?
Reply #6 –
Quote from: Will G  - 
Well, Larry - I usually find your advice spot on, and perhaps I'm missing something here. However, that doesn't sound significantly less complicated and adds risk I'd rather not have.

Compared to dual alternators, it introduces three single points of failure on the engine charging side of things, any of which could leave us stranded. First there's the single alternator, which is now heavily taxed performing both engine and house duties on a significantly larger battery bank. Second, the DC-DC charger is now needed to keep the engine battery topped off - not needed with dual alternators. Lastly, even for a larger single alternator directly charging a large and expensive lithium bank

The larger single alternator system would cost less, but with the addition of the DC-DC charger and Wakespeed the difference is not huge - to us, anyway. It also requires more space in the already limited area we plan on installing components under the fridge.
Sorry, I disappointed you. It wasn't criticism, just another way to accomplish a similar result, that's what we do here, exchange ideas. Your project design should work fine, it's just different than how I would approach it...I like simplicity. when practical.

Upgrading just the Factory alternator adds no new additional points of failure, especially compared to adding another alternator along with another belt, two pulleys, and idlers.  All new points of failure.

if doing this to my rig, instead of using a DC-DC charger, the existing 10i0-amp diode isolator would be reversed and run in parallel to charge the starting battery, providing a 200-amp isolator, more than enough to keep the starting battery and accessories happy.  A spare LD isolator relay would be used to disconnect the starting battery isolator from the coach battery when the engine is not running to prevent back-feeding.
Keeping both batteries charged is an absolute necessity. This would be a very basic and simple charging system with large capacity, once cabling is upsized and fused. There are other ways to charge both battery sets, this is just one of them.

High-output alternators are available with lithium regulators, both fixed and adjustable. This is not an uncommon upgrade now that lithiums have dropped in cost so much as well as the increase in robustness and intelligence of recent  BMSs. All the real magic happens in the BMS.
2003 Ford E-350 Super Duty 6.8L V10 415CID Alternator | Tucson Alternator
Lifetime alternator warranty $50
https://www.tucsonalternator.com/product/35-9999006/Voltage-Control-Kit-(For-Lithium-Battery-Use-Only)/H-ORG/
As for costing more, minus the wiring upgrades, the cost of the alternator and lithium regulator is $700 vs. $1900 for the dual alternator kit.

IMO, a properly sized alternator for the load, along with adequate cooling is no more likely to fail than running two smaller alternators. In 60 years of working on many types of equipment, I have never seen a well-speced alternator burn out. Yes, they wear out or suffer from a component failure, but not from overheating. Alternators automatically derate themselves as they get hot and have done so for for decades.

With the additional alternator, doing any type of work on the front of the engine will be just about impossible without removing the added alternator and supports.
Replacing a broken serpentine belt or a failed Factory alternator would be a huge project instead of a repair that takes normally an hour or so to perform.  Spending my career in industrial mechanical and electric maintenance and construction, I like to design things that are not difficult to work on...but that's just me.

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Dual alternator setup - remove diode isolator?
Reply #7 –
Quote from: Larry W  - 
Sorry, I disappointed you. It wasn't criticism, just another way to accomplish a similar result, that's what we do here, exchange ideas. Your project design should work fine, it's just different than how I would approach it...I like simplicity. when practical.

Not disappointed at all, Larry - and I didn't infer any criticism on your part at all. As always, thanks for chiming in.

My biggest concern with any motorhome is the chassis/engine side. With only minor exceptions, I've no interest in doing mechanical work - especially on the road. Those days are behind me. As such, chassis/engine issues will leave us stranded and/or spending days in local lodging while waiting on repairs. Issues on the house side are typically inconveniences, and for me - easier to troubleshoot and fix.

Perhaps the risks are small with a properly designed single alternator system as you described, I'll take your word for that. However, a big part of why I'm drawn to the dual alternator setup is the complete separation of house and engine charging. We're leaving the Ford side of things essentially stock. Most any mechanic will understand immediately what they are looking at.

Thanks again for your insights.
2002 26.5 MB

Previous: 2011 27 RB, 2005 24 TK