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r3meyer

Converting my Monaco to Lifepo4 batteries and 735watts of solar

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For those that might be interested here are video instructions to build a 200ah LifePo4 that has a high enough discharge rate to start anything and works in the voltage ranges of lead acid batteries so its about as close as you can get to a drop in replacement on a budget.  You gotta put it together yourself but it looks pretty easy and when you consider it has the same capacity of a pair of battle borns that would cost you more than double this does and this comes out to less than $600 so its quite a deal.  He gives a list of stuff to buy in the comments so all of the figuring out has been done and when you consider how fast you can charge this thing and how many more usable amp hours you can get this is more equivilant to two pairs of gc batts than the one pair as most would assume.  By the way this goes nicely into a box about the size of a dp start battery.  So far got my cells and the buss bars and waiting on the box and the bms.

Regarding charging these or any lithium battery with your alternator I would advise against it as if they are deeply discharged they will take all you can give it and possibly cook your expensive altenator.  Renology makes a dc to dc converter that is pretty cheap and will save your alternator and your trip home!

 

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17 hours ago, steinberg55 said:

Headway 38120 HP cells are rated at 8AH and 200A. A 4 pack of these will easily start a vehicle. And using the 300 amp BMS cut off above its viable to put in a buggy. and run off the alternator. In theory the alternator voltage will only be able to get the battery to 80% range, which is fine for lion for car starting. Few questions I can't find answers for.

1. Can alternator get high enough voltage to get BMS to cut off LifePo4 battery. I think, in normal operation, the vehicle has so much other electrical loads, that the alternator voltage won't get close to the 15 volt cut off. 

2. At that point will alternator charge current have no where to go and will take out diodes. 

 

 

I use one of these in the racecar, would work great for buggy use:

https://braillebattery.com/collections/green-lite/products/g20-1

Would not work in a SxS, since it wouldn't run the gigantic stereo and 14 whips for an hour at the hill.

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Well - I ordered 4 x 271aH cells from Alibaba and a 200amp BMS w/balance and high and low volt cutoff.

 

Now I will need to update my prehistoric converter/charger. Probably going to go with a inverter/charger in a 2000watt flavor. (I already have 1000watt inverter that powers about 40% of the plugs in the trailer) but this 2000watt inverter will power everything (except the ac - technically I can run the AC for about 1.2 hours of the batteries but thats just too harsh)

 

Also still need a good Monitor w/ Shunt and a new solar controller that wont make my Lifepo4 cells mad at me.

 

 

 

 

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1 hour ago, 1slomofo said:

Well - I ordered 4 x 271aH cells from Alibaba and a 200amp BMS w/balance and high and low volt cutoff.

 

Now I will need to update my prehistoric converter/charger. Probably going to go with a inverter/charger in a 2000watt flavor. (I already have 1000watt inverter that powers about 40% of the plugs in the trailer) but this 2000watt inverter will power everything (except the ac - technically I can run the AC for about 1.2 hours of the batteries but thats just too harsh)

 

Also still need a good Monitor w/ Shunt and a new solar controller that wont make my Lifepo4 cells mad at me.

I have a suggestion, if you don't mind. Both of my trailers have inverter/chargers, however...

that's not the best way to go for a LFP system with a BMS. The BMS can shut off a relay if the battery gets too low, removing the load. It can also shut off another relay if the battery gets too high, removing  the charger. However, in the case of an inverter/charger, both functions are on the same cables.

If the battery gets too low, it shuts off the line to the inverter, but that's also the charging line, so as long as the relay is open, the battery is not going to get recharged. You're better off buying one of the pure sine wave inverters off ebay and going with a Iota DLS-75 charger (or similar) and making sure the charger doesn't go over 14.6v. This way each relay controls a separate cable and isolates the load or charger as needed. 

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Posted (edited)
56 minutes ago, socaldmax said:

I have a suggestion, if you don't mind. Both of my trailers have inverter/chargers, however...

that's not the best way to go for a LFP system with a BMS. The BMS can shut off a relay if the battery gets too low, removing the load. It can also shut off another relay if the battery gets too high, removing  the charger. However, in the case of an inverter/charger, both functions are on the same cables.

If the battery gets too low, it shuts off the line to the inverter, but that's also the charging line, so as long as the relay is open, the battery is not going to get recharged. You're better off buying one of the pure sine wave inverters off ebay and going with a Iota DLS-75 charger (or similar) and making sure the charger doesn't go over 14.6v. This way each relay controls a separate cable and isolates the load or charger as needed. 

Good insight. I think I understand the logic here and I think we are on the same page actually.

 I have chosen to allow the BMS to do all the cutoff functions (ie: I am not using relays) The BMS I went with has a "separate port". for the charger side. So if I experience a cutoff scenario the battery will indeed be isolated from the inverter via that main 12v line. BUT I should still have a path to my solar charger through the "separate port" on the BMS for recharging...

In thinking about this more - I am not sure what would happen if the solar charger is causing an overvolt scenario?? I wonder if the BMS will cut the "Seperate Port " in that case.

 

Here is a picture of a similar(not the same model ) BMS that im using. -The middle copper tab is going to be charger pass through. (ignore that it says "common port")

 

bms.png

Edited by 1slomofo

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41 minutes ago, 1slomofo said:

Good insight. I think I understand the logic here and I think we are on the same page actually.

 I have chosen to allow the BMS to do all the cutoff functions (ie: I am not using relays) The BMS I went with has a "separate port". for the charger side. So if I experience a cutoff scenario the battery will indeed be isolated from the inverter via that main 12v line. BUT I should still have a path to my solar charger through the "separate port" on the BMS for recharging...

In thinking about this more - I am not sure what would happen if the solar charger is causing an overvolt scenario?? I wonder if the BMS will cut the "Seperate Port " in that case.

 

Here is a picture of a similar(not the same model ) BMS that im using. -The middle copper tab is going to be charger pass through. (ignore that it says "common port")

 

bms.png

That bms is what I have.  The problem you will run into is that bms does not balance for shit.  It’s better designed for smaller ah cells and I think will only move at 5ma.  The cells we are using have such large ah that you will need to find something that can move 5amps at a time.  Look into the deligreen balancers.  I think socdmax has a link for the 4s version.   

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1 hour ago, 1slomofo said:

Good insight. I think I understand the logic here and I think we are on the same page actually.

 I have chosen to allow the BMS to do all the cutoff functions (ie: I am not using relays) The BMS I went with has a "separate port". for the charger side. So if I experience a cutoff scenario the battery will indeed be isolated from the inverter via that main 12v line. BUT I should still have a path to my solar charger through the "separate port" on the BMS for recharging...

In thinking about this more - I am not sure what would happen if the solar charger is causing an overvolt scenario?? I wonder if the BMS will cut the "Seperate Port " in that case.

 

Here is a picture of a similar(not the same model ) BMS that im using. -The middle copper tab is going to be charger pass through. (ignore that it says "common port")

 

bms.png

If it can be programmed to cut off the charger port in the case of overvoltage and the load port in case of undervoltage, then you're in business.

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Just thought I would update this thread.  Got to use my solar setup out at glamis last weekend in my monaco.  Everything worked as it should.  The lowest I found the batteries was down to 138ah remaining in the morning after heavy use.  The batteries were back up to 200ah before noon each day.  Will probably start running my ice maker more in the mornings to use up the extra power because the whole system would be down to a 1-2 amp charge by 11am and I am wasting sun light.  Maybe I will sell a few bags of ice each day to neighbors to cover fuel costs LOL.

 

Anyone that is looking to upgrade to lithium there are a surge of Valence Lithium U27-12XP batteries on eBay right now.  They are top of the line and in my opinion as good if not better then battle born.  They are 138ah batteries and can be linked together.

https://www.ebay.com/itm/Valence-Lithium-Battery-U27-12XP-12V-138AH-1-766-kWh/264419014397?hash=item3d9099f6fd:g:YFoAAOSwOTldhmcU

Because they have all the BMS built in the cost is very very cheap.

Oddly enough the only issue I had was with my stupid chassis starting battery.  It ran down enough that I had to jump it from my lithium pack.  Fired right up after that.  I need to come up with a way to keep it trickle charging.

(ignore my monitor mounting job.  Need to put some black silicone around the edges.)

IMG_1112.jpg

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I run a Battery Tender plugged in to an outlet for the chassis battery.  If the coach has 120VAC, the chassis battery is getting a charge.

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2 minutes ago, Rockwood said:

I run a Battery Tender plugged in to an outlet for the chassis battery.  If the coach has 120VAC, the chassis battery is getting a charge.

Thats more then likely what I am going to do.  When the coach is at home I have grid tie that the solar from the motorhome will feed into the house and offset power usage so its always plugged in.  I just need to install one.

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1 minute ago, r3meyer said:

Thats more then likely what I am going to do.  When the coach is at home I have grid tie that the solar from the motorhome will feed into the house and offset power usage so its always plugged in.  I just need to install one.

It took me a while to install mine as well (bought it and was sitting on a shelf for years).  Had enough and finally installed it when I nuked yet another starting battery (yay Costco warranty)... :bigrin 

 

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