A few thoughts and questions replacing AGM with lithium in my Coachmen Beyond

[JonMN]

I am considering replacing my single 330AGM in my Coachmen Beyond with a single 300AH LiFePO4. Both are size 8D so I can fit the existing tray. The objective is more usable current between stops, but not overnight AC use.

Limitations: I am not in an area where I can get access to help for this project, but I have done a lot of wiring and mechanical maintenance on everything we own. This also means I do not have a lift, so I do not want to start rerouting cables that run under the van. Adding a second alternator is a wee bit beyond my confidence level, and the wiring without access to a lift would be daunting.

Charging: I have read a LOT of threads on this, and contacted a few battery vendors, but am having trouble choosing a DC-DC charger. My Ford alternator has 250 amp output, so it has a lot of potential. Thus I hate to put in just a 30 amp DC-DC. But most of the non-isolated DC-DC chargers are lower power. I do not see the need, in a Class B van, of having an isolated DC-DC unit. Renogy has a 60amp isolated. Could I just run both the negatives from an isolated to the grounding bus-bar? They also have a 50amp with solar input that is non-isolated, and some use it without the solar component as just a DC-DC. (Running two DC-DC in parallel is easy, but then I run into space limitations.)

The battery vendor is saying just skip the DC-DC and drop it in as a replacement, adjusting the I/C and solar input settings, of course. But to me, 300AH is pretty big potential load for an alternator. On the other hand, if the battery is not depleted too far, what is the current draw?

When I think of how we use the van, I also want to see if the idea makes sense. Right now, on long drives in the sun, we can run the 12V Premier AC, the 12V NovaKool refrigerator, and do some charging with power coming in from the alternator. As soon as I add a DC-DC, the power going to the coach in will be limited, so I would be close to breaking even or even losing charge as we drive if the coach AC was running.

Any thoughts would be welcome. Thanks!

 

[booster]

I am considering replacing my single 330AGM in my Coachmen Beyond with a single 300AH LiFePO4. Both are size 8D so I can fit the existing tray. The objective is more usable current between stops, but not overnight AC use.

Limitations: I am not in an area where I can get access to help for this project, but I have done a lot of wiring and mechanical maintenance on everything we own. This also means I do not have a lift, so I do not want to start rerouting cables that run under the van. Adding a second alternator is a wee bit beyond my confidence level, and the wiring without access to a lift would be daunting.

Charging: I have read a LOT of threads on this, and contacted a few battery vendors, but am having trouble choosing a DC-DC charger. My Ford alternator has 250 amp output, so it has a lot of potential. Thus I hate to put in just a 30 amp DC-DC. But most of the non-isolated DC-DC chargers are lower power. I do not see the need, in a Class B van, of having an isolated DC-DC unit. Renogy has a 60amp isolated. Could I just run both the negatives from an isolated to the grounding bus-bar? They also have a 50amp with solar input that is non-isolated, and some use it without the solar component as just a DC-DC. (Running two DC-DC in parallel is easy, but then I run into space limitations.)

The battery vendor is saying just skip the DC-DC and drop it in as a replacement, adjusting the I/C and solar input settings, of course. But to me, 300AH is pretty big potential load for an alternator. On the other hand, if the battery is not depleted too far, what is the current draw?

When I think of how we use the van, I also want to see if the idea makes sense. Right now, on long drives in the sun, we can run the 12V Premier AC, the 12V NovaKool refrigerator, and do some charging with power coming in from the alternator. As soon as I add a DC-DC, the power going to the coach in will be limited, so I would be close to breaking even or even losing charge as we drive if the coach AC was running.

Any thoughts would be welcome. Thanks!

A good place to start is to look and see how big the wiring is to the 330ah AGM battery and then size your current limiting to match that size. It is likely quite large if you can run the AC and frig and charge batteries at the same time. You can get large B to B chargers up to at least 120amps. Another option would be on of the current limiting split charge controls like this one:


https://www.mastervolt.com/products/charge-mate-to-connect-two-batteries/charge-mate-pro-90/


They also make a 40 amp version. If the voltage of the alternator is close enough for the lithium batteries the split charge would work well as long as you could also turn off the charging when they get full which is always a good idea.


The 300ah lithium should be able to handle the 90ish amps but be sure to check with the manufacturer as to what max charge rate is allowed.

 

[JonMN]

A good place to start is to look and see how big the wiring is to the 330ah AGM battery and then size your current limiting to match that size. It is likely quite large if you can run the AC and frig and charge batteries at the same time. You can get large B to B chargers up to at least 120amps. Another option would be on of the current limiting split charge controls like this one:


https://www.mastervolt.com/products/charge-mate-to-connect-two-batteries/charge-mate-pro-90/


They also make a 40 amp version. If the voltage of the alternator is close enough for the lithium batteries the split charge would work well as long as you could also turn off the charging when they get full which is always a good idea.


The 300ah lithium should be able to handle the 90ish amps but be sure to check with the manufacturer as to what max charge rate is allowed.

Thanks for the interesting information. I checked the charging limit, and it's a whopping 200 amp, so that should not be a limitation.

I still wonder if I would be giving up something by the change. I am thinking specifically of driving along and running the 12v ac. The refrig draw is so low a little solar input would keep equal the loss. The AC, however, might draw more than the DC-DC charger, so I would actually be at a bit of a loss. Of course, when I stop I could top it up pretty quick with the generator.

FYI, this is the battery I am looking at: LINK

 

[@Michael]

Renogy has a 60amp isolated. Could I just run both the negatives from an isolated to the grounding bus-bar?

Yes.

The battery vendor is saying just skip the DC-DC and drop it in as a replacement,

Which make/model BIM do you have, and what gauge wire from the chassis battery back to the BIM, and what's the capacity of the breaker that's in between the chassis batteries and the BIM?

(Mine came with a Precision Circuits BIM-160 and an 8-gauge wire from the chassis battery to the BIM, roughly 10-ft. long. If you are running a 12V A/C while driving, yours might be different.)

But to me, 300AH is pretty big potential load for an alternator. On the other hand, if the battery is not depleted too far, what is the current draw?

Unlike AGM's, LiFePo4's have very low internal resistance, and charge at high rate until full. If yours has a similar type of BIM, the LiFePo4 and the chassis AGM batteries will be in parallel when the BIM relay is closed. The alternator would 'see' a very low resistance load until the LiFePo4 is fully charged and would output quite a lot of amps (>100 amps?). I suspect that the only limit on alternator output would be the resistance of the wire from the under-seat chassis batteries to wherever the BIM is installed.

The other thing to think about is that the BIM that mine came with cycles on for one hour each time the vehicle is started, after which it disconnects. That prevents a full charge to coach battery unless you stop the engine periodically. Yours might be different.

A B2B would be much more flexible.

 

[JonMN]

Thanks Michael. Mine is also has a BIM-160. I will check next time I have it open to see the gauges used. I know there is a really heavy cable heading off to the AGM, which is in the rear of the van. The cable from the chassis battery is lighter, as is the cable from the BIM to the disconnect solenoid.

I do think a DC-DC would be an easy replacement for the BIM.

 

[phantomjock]

First, "I know nothZing" (not Sgt. Schultz), about a Coachman Beyond.

BATTERY CHOICE: I'm pretty sure the drop in idea is pretty good one. Why not "give it a go and see what you'd like next? But - My concern would be the low resistance and charging capability of the LiFePO4 vs AGMs. The Lithium would take everything your alternator could give - up to their max charge rate, and as booster has mentioned in the past (AFAIR), the possibility of overheating the alternator and burn-out could be very real.

ALTERNATOR: I am not sure how easy a second alternator would be to install - again - no knowledge of Coachman, but up-sizing the existing alternator should be pretty easy and something you "should" be able to do - even in the driveway. As booster suggested, you'd want to match max charge rate of the alternator and the battery bank. As a "gouge," I looked at 400Ah batteries and the max input charge ranged from 100Amps to 120Amps, even up to 200Amps in one case. That said, the battery bank will accept what is required - not all of the alternator potential capacity. So, a 200Amp alternator would provide about 50% of its capacity. Any excess capacity of the alternator, serves as a margin of safety. Check for the alternator hot rated output at RPM too. For rapid charging you'd want that overhead margin of safety, in either in a single alternator or dual setup.

TOOL LIMITATIONS: A set of ramps and jack stands would get you underneath the vehicle to inspect or, if needed and give some insight to the chassis. Useful if you ever decided to run cable there. I did all my work, cable runs, battery bank, etc, in the driveway using those simple key tools.

At the outset, I declared my lack of specific Coachman knowledge. Hopefully the information I've added form my recent upgrades may be of some use. Best of luck.

Cheers - Jim

 

[JonMN]

^^^ Thanks Jim! I have read a LOT of threads on this topic. Kind of interesting how many opinions you can get. I suppose part of the discussion depends upon how much capacity you have. If you are going 100 or 200AH, most solutions might work. 300 Maybe. Higher you need to go to more serious charging options.

I am still a little confused on lithiums. When I look at specs, they all have BMS that limits charging current, but I think this is just by stopping charging. I take this to mean that if I had a battery that was 90% discharged, and no other device between the battery and alternator, it might exceed the amperage limit of the BMS and just quit charging. Not sure if this means the battery keeps checking for a lower current supply continuously or needs some type of BMS reset.

I think consensus is that the safest approach is the DC-DC charger. Perhaps I could free up enough space to run two in parallel. Redarc is expensive, but compact, easy to wire, and is reported to run cooler than some other options.

 

[booster]

^^^ Thanks Jim! I have read a LOT of threads on this topic. Kind of interesting how many opinions you can get. I suppose part of the discussion depends upon how much capacity you have. If you are going 100 or 200AH, most solutions might work. 300 Maybe. Higher you need to go to more serious charging options.

I am still a little confused on lithiums. When I look at specs, they all have BMS that limits charging current, but I think this is just by stopping charging. I take this to mean that if I had a battery that was 90% discharged, and no other device between the battery and alternator, it might exceed the amperage limit of the BMS and just quit charging. Not sure if this means the battery keeps checking for a lower current supply continuously or needs some type of BMS reset.

I think consensus is that the safest approach is the DC-DC charger. Perhaps I could free up enough space to run two in parallel. Redarc is expensive, but compact, easy to wire, and is reported to run cooler than some other options.

One thing that I like to stress to all is that I don't thing the BMS is the right place to control charging and really are a self protection of the battery from destruction. The usually stop charging by disconnecting at the max allowable voltage of the battery which is not generally considered the best place to stop charging, for instance. Same thing with temp disconnects. And of course remember you need a way to recover from BMS disconnects.


Unless things have changed I don't think most BMS units will disconnect on high current, but I could be wrong on that. The "max charge rate" is what the manufacturers have determined to be maximum that the battery can handle on a regular basis even though they will accept much more in most cases and they leave it up to the user to provide that limiting. We recently had a case of BMS failure that was probably related to charge rate on here.


The whole world of lithium is evolving into being similar to the AGMs now that prices have come down, and that means that decisions need to be made to spend more for better controls or accept the shorter battery life that poor controls will give you. I don't think it is quantified yet so not as easy as it is with AGMs. There are lots of tough decisions to make and way to many opinions as to what is best that vary from "just drop in lithium" to "you need to build a very complex system".

 

[JonMN]

^^^ I think you got it right! OK, if I don't talk myself out of this completely and just stay with my 330AH AGM (which is not that bad an option) I think I will go with this:

2-50A DC-DC chargers in parallel to provide 100A charging.

Logic:
1. I have 250 amp alternator to start with, so no problem there.
2. If I am driving and want the 12volt air conditioner running, it should still deliver a little charge to the battery. The 12V A/C start up is potentially 100amp, but based on other owners measurements it drops to 50amp or so after starting.
3. The 12volt refrigerator has a very low draw, so not really a factor.

 

[booster]

^^^ I think you got it right! OK, if I don't talk myself out of this completely and just stay with my 330AH AGM (which is not that bad an option) I think I will go with this:

2-50A DC-DC chargers in parallel to provide 100A charging.

Logic:
1. I have 250 amp alternator to start with, so no problem there.
2. If I am driving and want the 12volt air conditioner running, it should still deliver a little charge to the battery. The 12V A/C start up is potentially 100amp, but based on other owners measurements it drops to 50amp or so after starting.
3. The 12volt refrigerator has a very low draw, so not really a factor.

If you are doing AGM you could probably save some space by using the linked above 90 amp limited split charge relay as the voltages from the engine charging will not be bad for AGM batteries. Just add a remote disconnect switch for the charging to the coach for when they are full if you drive long distances or come off shore power overnight often and you would be good to go. You might also consider and battery monitor at the same time as they are always a good idea with any system.

 

[rlum-JAY]

I am considering replacing my single 330AGM in my Coachmen Beyond with a single 300AH LiFePO4. Both are size 8D so I can fit the existing tray. The objective is more usable current between stops, but not overnight AC use.

Limitations: I am not in an area where I can get access to help for this project, but I have done a lot of wiring and mechanical maintenance on everything we own. This also means I do not have a lift, so I do not want to start rerouting cables that run under the van. Adding a second alternator is a wee bit beyond my confidence level, and the wiring without access to a lift would be daunting.

Charging: I have read a LOT of threads on this, and contacted a few battery vendors, but am having trouble choosing a DC-DC charger. My Ford alternator has 250 amp output, so it has a lot of potential. Thus I hate to put in just a 30 amp DC-DC. But most of the non-isolated DC-DC chargers are lower power. I do not see the need, in a Class B van, of having an isolated DC-DC unit. Renogy has a 60amp isolated. Could I just run both the negatives from an isolated to the grounding bus-bar? They also have a 50amp with solar input that is non-isolated, and some use it without the solar component as just a DC-DC. (Running two DC-DC in parallel is easy, but then I run into space limitations.)

The battery vendor is saying just skip the DC-DC and drop it in as a replacement, adjusting the I/C and solar input settings, of course. But to me, 300AH is pretty big potential load for an alternator. On the other hand, if the battery is not depleted too far, what is the current draw?

When I think of how we use the van, I also want to see if the idea makes sense. Right now, on long drives in the sun, we can run the 12V Premier AC, the 12V NovaKool refrigerator, and do some charging with power coming in from the alternator. As soon as I add a DC-DC, the power going to the coach in will be limited, so I would be close to breaking even or even losing charge as we drive if the coach AC was running.

Any thoughts would be welcome. Thanks!

Here is a link to a couple with Coachmen Beyond who replaced their AGM with lithium. They just did a straight exchange.

 

[JonMN]

^^^ neat link--I had not seen this one yet. It's encouraging to see actual videos--makes the project more approachable. Interesting that they did not seem to change out anything other than a couple charging settings (I/C and solar, I assume)

 

[JonMN]

Next question: Heated vs unheated?

Our Class B stays in a nice, but unheated garage. Since this garage does have one heated wall, it runs about 20F warmer than ambient all winter. I do not think I have ever seen it below 15F, even when outdoor was -20F.

But since the van is in the garage, it's nice to leave it on shore power in case I want to run down and tweak something.

If I had a heated battery, the heater would, unfortunately, be running all winter as the inverter/charger would be keeping the battery charged. I'm thinking this might wear out the heater.

If I had an unheated battery, I could be on shore power and the BMS in the battery would just not attempt to charge in the coldest months.

We never plan on camping in the cold. Any winter drives would be to get somewhere considerably warmer, where it could start charging as normal.

Cost is identical on the batteries I am looking at. Would you go heated or not?

[PS: No way to relocated batteries inside, which would alleviate the concern.]

 

[booster]

Our Class B stays in a nice, but unheated garage. Since this garage does have one heated wall, it runs about 20F warmer than ambient all winter. I do not think I have ever seen it below 15F, even when outdoor was -20F.

But since the van is in the garage, it's nice to leave it on shore power in case I want to run down and tweak something.

If I had a heated battery, the heater would, unfortunately, be running all winter as the inverter/charger would be keeping the battery charged. I'm thinking this might wear out the heater.

If I had an unheated battery, I could be on shore power and the BMS in the battery would just not attempt to charge in the coldest months.

We never plan on camping in the cold. Any winter drives would be to get somewhere considerably warmer, where it could start charging as normal.

Cost is identical on the batteries I am looking at. Would you go heated or not?

[PS: No way to relocated batteries inside, which would alleviate the concern.]

I would get heated but would want it on an on/off switch override also. I don't know where the battery is located in your van but if it is in a cold area while driving, it could take a long time to thaw out after you get to a warm place and need it. Heater give you the opportunity to recover the ability to use and charge as you drive. If they are inside a van in an area that sees heat readily you could probably get by without, but wouldn't be able to preheat before leaving.



If you can't control the heat, it might be better to get the regular battery and add heating pads and your own control or switched power to them.

 

[reilym]

Our Class B stays in a nice, but unheated garage. Since this garage does have one heated wall, it runs about 20F warmer than ambient all winter. I do not think I have ever seen it below 15F, even when outdoor was -20F.
But since the van is in the garage, it's nice to leave it on shore power in case I want to run down and tweak something.
If I had a heated battery, the heater would, unfortunately, be running all winter as the inverter/charger would be keeping the battery charged. I'm thinking this might wear out the heater.
If I had an unheated battery, I could be on shore power and the BMS in the battery would just not attempt to charge in the coldest months.
We never plan on camping in the cold. Any winter drives would be to get somewhere considerably warmer, where it could start charging as normal.
Cost is identical on the batteries I am looking at. Would you go heated or not?
[PS: No way to relocated batteries inside, which would alleviate the concern.]

If you're not cold weather camping, I would opt for the unheated battery, as long as it has a low temperature disconnect to protect the battery. My two 100 Ah LiFePO4s do not have that and I have to manually disconnect them when we're travelling through the cold to escape Michigan winters. It would be nice to not have to worry about that. Heated batteries have their place for heavy use in cold weather, but it's another drain on the battery something else to break. The lithiums will happily survive the kind of winter storage you are talking about without charging as long as they have a decent charge when you put them away.

Renogy has some problems with customer service, but the 60 amp DC-DC I installed 3 years ago has not let me down. I have a 220 amp alternator that was sometimes putting 150 amps back to the Li batteries before I installed this. See that thread here.

 

[Davydd]

My last two Class Bs had electric heating pads in the previous one with lithiun batteries under the chassis and an electric heating plate under the lithium batteries inside in my current one. The previous one was parked outside with shore power. My current one is in a heated garage and the heating plate I doubt would ever come on. If it is 15F outside shore power is useless because if you have a smart enough BMS your batteries will not receive a charge. With both Class Bs I have winter camped at least 5 days in a row in Minnesota and Michigan's UP. Battery heat was necessary especially if it gets down to a battery destroying -4F and I have camped at -15F with shore power. I have taken 2 or more days from Minnesota when traveling south and boon docked at 0F overnight to get above freezing temperatures. I think a battery heater and shore power are necessary in Minnesota for the lithium house batteries unless stored in the winter in a 40F plus indoor space. There are just too many variables like -4F to keep batteries above and 32F (some say 40F) to charge to take a chance.

 

[JonMN]

Renogy has some problems with customer service, but the 60 amp DC-DC I installed 3 years ago has not let me down. I have a 220 amp alternator that was sometimes putting 150 amps back to the Li batteries before I installed this. See that thread here.

I was looking at that one. It's isolated. Just for my info, where did you attach the two grounds? Did you really run them to the batteries?

In my van, there is a grounded busbar next to the BIM. Lots of heavy ground cables coming out of it. I am thinking with a non-isolated DC-DC like some of the Renology, some Victrons or the Redarcs, I could run the ground to this busbar and save a lot of extra wiring. Of course the positives of the coach and chassis batteries are attached to the BIM-160, so that's a straight swap.

PS: thanks all for the comments on heated vs non-heated. I am leaning towards a heated battery from Lithiumhub. It's a heated 300AH with a size that makes it a direct replacement of the 8D size AGM. Bluetooth BMS is also a plus for me.

PSS: Fun to see a few folks from Minnesota!

 

[Davydd]

I forgot to mention, the battery heat goes through the shore power to the battery because in boon docking you need the heat and your battery is the only source. Self feeding but with high amp hour batteries it is not a problem overnight boon docking.

I keep my van plugged-in to shore power in the heated garage because I want to use my van as a bathroom at the very least.

 

[booster]

I forgot to mention, the battery heat goes through the shore power to the battery because in boon docking you need the heat and your battery is the only source. Self feeding but with high amp hour batteries it is not a problem overnight boon docking.

I keep my van plugged-in to shore power in the heated garage because I want to use my van as a bathroom at the very least.

The setup you have is pretty common, but for me I would not want it that way in and by itself.


Shore power heat of batteries, absolutely, especially if parked outside in the winter and you have power available. No heat except from batteries when off shore power, no I wouldn't want that. It would be very simple to have a switchable power to heating pads from the van alternator/charging system so they can be warmed that way when shore power is not available or they are offline due to cold. If you don't have that and leave Minnesota with them in cold shut down and not in a heated area you can't get them back online or have 12v power or 110v to van until you get to a warm enough area to thaw them out and that can take a while if it is only 10* above their cutoff point.

 

[reilym]

I was looking at that one. It's isolated. Just for my info, where did you attach the two grounds? Did you really run them to the batteries?

No, I did not. Both negative terminals go right to the chassis bus <2 feet from the charger. For the alternator feed to the Renogy, I used the dual 2/0 charging cables that used to be connected to the under hood isolator (now a manual disconnect switch) that came in the RV. As 2016 was PW's first foray into LiFePO4, not a lot had been worked out as far as Lithium goes, so they just doubled up on the charging cables and just let the electrons fly unregulated. The original owner must have shorted system at some point, because on the trip from the purchase point in Phoenix back home to Michigan, it I noticed we were not charging from the alternator and later discovered both 150 amp inline fuses were blown. Now PW has gone back to a single cable and a Mastervolt DC-DC charger. If I ever need 20' of 2/0, I can just canabalize it from the original feed since a second cable is superfluous. For now, I leave it there since I can just do an emergency bypass of the DC-DC in case it fails on the road. I think you'll be thrilled with your decision to go lithium. Good luck!