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Old 06-06-2021, 05:53 PM   #1
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Replacing the generator

I am having a hard time getting my 6500 Oman fixed. Has anyone pondered replacing the generator with batteries and 240Volt inverter? What would the cost be? How much battery would it take? How long would it last? I'm thinking if the generator was removed their would be lots of room for the batteries and inverter.
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Old 06-06-2021, 06:49 PM   #2
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Hi

Ok, the "easy* way to do 6KW would be with a 5KW Victron Multi Plus

https://shop.pkys.com/Victron-Energy...DC_p_2851.html

Seems to be $3,379. It also acts as a charger (which you *will* need).

5KW at 12V is a bit over 450A, even at 90% efficiency.

Simply to keep that going without nuking the batteries will mean at least 5 and more likely 10 100AH lithium batteries. They are about $900 each so $4,500 to $9,000 simply to get it running.

If you want to run full up for 24 hours, that will get you to 10,800 AH. You now are up to 11 batteries. Two days doubles that to 22.

Weight wise, the inverter is 75 pounds. The batteries are about 31 pounds each. You will have 300 to 650 pounds of batteries.

How long will you run full power? Who knows.... Run at half power and your 1 day batteries last 2 days. I would not go below 10 batteries for that size inverter ....

6KW replacement

https://www.norwall.com/products/Cum...6.0HDKAH-1044/

looks like it weighs 420 pounds. Cost $8K.

Generator is no bigger / no heavier and a bit cheaper.

Generator runs down and you need more diesel. Batteries run down and you either need shore power or a generator ( yes a couple KW of solar would also do the job, not going to fit on an AS ...).

Bob
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Old 06-07-2021, 08:05 AM   #3
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Hi

Thinking about this a bit more:

I'd bet that the generator replacement is a quick swap out. Pull one and the other drops right in. No change in wiring or anything else.

Putting in the inverter and batteries is going to be a *lot* of work. Rewiring this and rewiring that is only part of it. Sure, you can work for free for a month or three. Unless making up cables and welding supports is your hobby, I don't really see that as zero cost.

Bob
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Old 06-07-2021, 01:02 PM   #4
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I tried doing the inverter thing 20 years ago in the Snap-On truck, killed an alternator, cooked 8 batteries, and let some smoke out. A huge waste of time and money. When the truck was new it came with a Honda 6100, liquid cooled, 3600 RPM.....went through 3 of them.....junk. Switched to an air cooled Onan 6500, 1800 RPM, OK, but only lasted about 2600 hours, went through 2 of them, switched to an Onan 7500, 1600 RPM.....great got 11,000 hours out of her before she broke a breather pipe off the valve cover and set itself on fire. Replaced it with an Onan 8000 , 1600 RPM......still in use today with 7300 hours on it, had the 7500 rebuilt $5400.00 and kept it as a spare. The stainless steel box that I had built for the Snap-On truck cost $6,000.00 ......was well worth it. When I was going to switch the 370LE from a gas 460 engine to a 6.6 Duramax I bought an Onan 7500SD COMMERCIAL diesel 2cylinder which would have fit into the original 370LE compartment with a little modification. As it turns out I rebuilt the 460 and still have the new diesel Onan in stock ! Regards, Bob
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Old 06-08-2021, 07:13 AM   #5
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Quote:
Originally Posted by uncle_bob View Post
Hi

Ok, the "easy* way to do 6KW would be with a 5KW Victron Multi Plus

https://shop.pkys.com/Victron-Energy...DC_p_2851.html

Seems to be $3,379. It also acts as a charger (which you *will* need).

5KW at 12V is a bit over 450A, even at 90% efficiency.

Simply to keep that going without nuking the batteries will mean at least 5 and more likely 10 100AH lithium batteries. They are about $900 each so $4,500 to $9,000 simply to get it running.

If you want to run full up for 24 hours, that will get you to 10,800 AH. You now are up to 11 batteries. Two days doubles that to 22.

Weight wise, the inverter is 75 pounds. The batteries are about 31 pounds each. You will have 300 to 650 pounds of batteries.

How long will you run full power? Who knows.... Run at half power and your 1 day batteries last 2 days. I would not go below 10 batteries for that size inverter ....

6KW replacement

https://www.norwall.com/products/Cum...6.0HDKAH-1044/

looks like it weighs 420 pounds. Cost $8K.

Generator is no bigger / no heavier and a bit cheaper.

Generator runs down and you need more diesel. Batteries run down and you either need shore power or a generator ( yes a couple KW of solar would also do the job, not going to fit on an AS ...).

Bob
Thanks Bob. Was just doing a search for 'modified sine wave inverters'. I can buy a brand new generators cheaper (https://www.norwall.com/products/Cum...-70HGJAB-6756/ than one of them babies. Got a guy that says he can fix my generator. Been waiting 2 months for that to happen. Seems no one can/will do anything in a timely meaner.
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Old 06-08-2021, 07:38 AM   #6
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Depending on what’s wrong with it if you get the parts we can pull it out at the get together and I’ll rebuild it for you…..about 3 hours on a picnic table….I have the tools…….dammmmmmm did I just offer that ??? Regards, Bob
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Old 06-08-2021, 08:39 AM   #7
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Love seeing numbers quoted that relate to lead acid/AGM/ or LiFePO4 that mimic those form factors. $500 will buy to 320ah (4s)/250a BMS (Daly), $900 for 640ah (4s2p)/250ah.
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Old 06-09-2021, 07:57 AM   #8
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Originally Posted by martin300662 View Post
..... $500 will buy to 320ah (4s)/250a BMS (Daly), $900 for 640ah (4s2p)/250ah.
Hi

As long as you don't mind the resulting fire, that sounds like a great way to go. Yes, there are documented cases of folks doing this sort of thing and having their RV go up in flames ....

Bob
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Old 06-09-2021, 09:17 AM   #9
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Quote:
Originally Posted by uncle_bob View Post
Hi

As long as you don't mind the resulting fire, that sounds like a great way to go. Yes, there are documented cases of folks doing this sort of thing and having their RV go up in flames ....

Bob
Yes, this can happen. No it wont happen, if you do it properly.
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Old 06-10-2021, 07:03 AM   #10
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Yes, this can happen. No it wont happen, if you do it properly.
Hi

Just how much do you *know* about the internals of that eBay BMS?

Bob
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Old 06-10-2021, 07:15 AM   #11
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Hi

Just how much do you *know* about the internals of that eBay BMS?

Bob
The specs are published, which is why I 'quoted' that specific BMS, not 'any old BMS'.
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Old 06-10-2021, 08:16 AM   #12
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Well good news! The guy finally got to the generator. He replaced everything that should have been replaced that hasn't ever been serviced and the reason it wouldn't run is it has a broken intake valve spring. None in stock but they're going to make one. Glad I didn't try to get Oman/Cummins to work on it again. Without electronic to hook their scanner to they have no idea what to fix. That lessen only cost me $700
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Old 06-10-2021, 03:07 PM   #13
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Quote:
Originally Posted by uncle_bob View Post
Hi

Thinking about this a bit more:

I'd bet that the generator replacement is a quick swap out. Pull one and the other drops right in. No change in wiring or anything else.
.....

Bob

Unfortunately that is not the case. The new cummins /onan generators come in a housing that do not fit the classic Motorhome Generator compartment. The fuel and power supply is on the left instead of the original right.

The modifications required vary from coach to coach, the mid coach compartments being the most difficult to extend.

Currently there is no drop in replacement RV generator available.
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Old 06-11-2021, 05:54 AM   #14
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I think we got lucky on our 270. It was built with the optional gen set Kohler 7k. It may have required a bigger compartment, so size-wise the new Onan dropped in with air and service holes cut out of the bottom

Connection wise, it was not a drop in, requiring an extension to the 12v line and wire harness to new control panel
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Old 06-11-2021, 06:54 AM   #15
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The specs are published, which is why I 'quoted' that specific BMS, not 'any old BMS'.
Hi

The spec sheet on that BMS is very brief. Since they come from all over, it's never quite clear if you have a legit version or some sort of "clone". Given the source, clones are unfortunately a common thing. There's a *lot* more that goes into that BMS than a simple spec sheet.

Bob
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Old 06-11-2021, 06:55 AM   #16
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Originally Posted by PeterH-350LE View Post
Unfortunately that is not the case. The new cummins /onan generators come in a housing that do not fit the classic Motorhome Generator compartment. The fuel and power supply is on the left instead of the original right.

The modifications required vary from coach to coach, the mid coach compartments being the most difficult to extend.

Currently there is no drop in replacement RV generator available.
Hi

That complicates things a bit.

Bob
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Old 06-11-2021, 07:23 AM   #17
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Quote:
Originally Posted by uncle_bob View Post
Hi

The spec sheet on that BMS is very brief. Since they come from all over, it's never quite clear if you have a legit version or some sort of "clone". Given the source, clones are unfortunately a common thing. There's a *lot* more that goes into that BMS than a simple spec sheet.

Bob
Understand and don't disagree Bob, but to me that is part of due diligence.

I would not buy a mainstream brand from what is supposedly 'their manufacturer' in China/overseas. But I would happily buy a unit from source (DALY is a Chinese brand and you can buy from their own store), if that technology is supported with QA/specs and proven in the field. Equally I would not buy, even a branded part (a good example is the DALY Smart BMS), based just on QA/specs are there are numerous reports of the 'smarts' failing. As I say you have to do your due diligence.

In the same way as you have to understand the likelihood of the MH breaking down each time you go out, and the minimal survival rating with involved in a crash, user assumes risks but that means user understands risks, and makes an informed decision.
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Old 06-11-2021, 09:09 AM   #18
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Understand and don't disagree Bob, but to me that is part of due diligence.

I would not buy a mainstream brand from what is supposedly 'their manufacturer' in China/overseas. But I would happily buy a unit from source (DALY is a Chinese brand and you can buy from their own store), if that technology is supported with QA/specs and proven in the field. Equally I would not buy, even a branded part (a good example is the DALY Smart BMS), based just on QA/specs are there are numerous reports of the 'smarts' failing. As I say you have to do your due diligence.

In the same way as you have to understand the likelihood of the MH breaking down each time you go out, and the minimal survival rating with involved in a crash, user assumes risks but that means user understands risks, and makes an informed decision.
Hi

My only real point is that some (but not all) manufacturers design their batteries from the ground up. (Maybe in house, maybe another way). They do a full up design on the BMS to be sure all of the grubby details get taken care of. I used to do that sort of thing for a living, there are *always* a lot of grubby details. If you simply buy a generic BMS, you have no way of digging that deep into it.

Bob
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