another DIY roadtrek lithium - newb needs help

[bumpersignal]

I have a '15 Roadtrek TS. It has a second alternator charging 4 coach agm batteries and connects to a renogy 3000w inverter. All 4 of my agm were on their way out, holding very little charge so I thought it was a good time to start converting to lifepo4.

I purchased a single battleborn GC3 (280Ah) battery which will fit in the rear battery tray, replacing two of the original agms. Originally the plan was to replace the two under hood 6v agm batteries with a single 12v automotive battery that will then connect to two sterling 60amp DC to DC chargers and then connect the existing 4awg cable that goes from hood to rear battery. Is it a bad idea to install the sterling chargers under hood where there will be a lot of heat?

After reading more threads in here some people are for the dc to dc charging and some are about installing a ballmer. When I started my research I shied away from ballmer because I heard those sometimes fail causing battery issues. Is this an overblown concern and therefore should I be leaning more toward the ballmer straight to lithium skipping dc to dc?

[rowiebowie]

Originally Posted by bumpersignal

I have a '15 Roadtrek TS. It has a second alternator charging 4 coach agm batteries and connects to a renogy 3000w inverter. All 4 of my agm were on their way out, holding very little charge so I thought it was a good time to start converting to lifepo4.

I purchased a single battleborn GC3 (280Ah) battery which will fit in the rear battery tray, replacing two of the original agms. Originally the plan was to replace the two under hood 6v agm batteries with a single 12v automotive battery that will then connect to two sterling 60amp DC to DC chargers and then connect the existing 4awg cable that goes from hood to rear battery. Is it a bad idea to install the sterling chargers under hood where there will be a lot of heat?

After reading more threads in here some people are for the dc to dc charging and some are about installing a ballmer. When I started my research I shied away from ballmer because I heard those sometimes fail causing battery issues. Is this an overblown concern and therefore should I be leaning more toward the ballmer straight to lithium skipping dc to dc?

I vote for the DC to DC route. Since my coach batteries are lithium and engine battery is lead-acid, I wanted complete separation plus proper lithium charging profile for my coach batteries and it seemed the safest and easiest way to go.

I have the same Renogy 3000W Inverter/Charger as you and Renogy 40A DC to DC to charge my Renogy 2 x 100h Renogy batteries while driving. I changed nothing under my hood, and all is working fine after 3 years. Your 2nd alternator should easily support a 60A DC to DC, but I stayed with 40A with my single OEM 165A alternator.

Good luck and let us know how it goes.

[bumpersignal]

Originally Posted by rowiebowie

I vote for the DC to DC route. Since my coach batteries are lithium and engine battery is lead-acid.

Thanks for the input. For the battery that connects to the 2nd alternator, I want to choose a low cost lead acid battery as well. I'm unfamiliar with what specs of battery I'll need for this. Such as if I get a standard yellow top optima, would it have enough output to do 60A to the dc2dc charger? What if I hookup TWO dc2dc chargers to that battery?

[rowiebowie]

Originally Posted by bumpersignal

Thanks for the input. For the battery that connects to the 2nd alternator, I want to choose a low cost lead acid battery as well. I'm unfamiliar with what specs of battery I'll need for this. Such as if I get a standard yellow top optima, would it have enough output to do 60A to the dc2dc charger? What if I hookup TWO dc2dc chargers to that battery?

I guess I don't understand second alternators as I assumed the 2nd one was devoted solely to charging the coach batteries (hence the need for a DC to DC) and the first alternator charges solely the engine battery or batteries.

[bumpersignal]

Originally Posted by rowiebowie

I guess I don't understand second alternators as I assumed the 2nd one was devoted solely to charging the coach batteries (hence the need for a DC to DC) and the first alternator charges solely the engine battery or batteries.

Im my situation, the idea is to have the 2nd alternator charge a lead acid battery first and then the dc2dc will use that battery to charge the bigger lithium. The lead acid as the first battery is needed because the alternator doesn't have a balmar to support lithium directly.

[avanti]

I vote for getting a Balmar. Much more straightforward, and possibly cheaper.

I don't really believe that they are particularly unreliable if properly installed. Mine, at least, has been flawless for 7 years. And, you can always carry a spare if you are worried.

[bumpersignal]

Originally Posted by avanti

I vote for getting a Balmar. Much more straightforward, and possibly cheaper.

I don't really believe that they are particularly unreliable if properly installed. Mine, at least, has been flawless for 7 years. And, you can always carry a spare if you are worried.

Which one do you recommend? MC614 Balmar ?

[booster]

I would also vote for the Balmar as you can do you current limiting on it as well as get charge profile. The Balmar will allow as much as approx 50% turndown so should be quite close to what you need.



If you do the B to B chargers, you would be best off with a 40 amp for the AGM and a 120 amp for the lithiums to get them charged. If you do decide to charge the lithium off the AGM which probably isn't a great was to do it as the lithium fills so quickly on the alternator, you would be back to a lot switching. You could just use the AGM as backup and for getting the alternator activated if the lithiums are offline.

[avanti]

Originally Posted by bumpersignal

Which one do you recommend? MC614 Balmar ?

Yep. That's the one.

[rowiebowie]

Still confused. Why is a Balmar and intermediate lead-acid battery necessary to get the proper charging profile to the new lithium coach batteries since it is precisely the job of a DC to DC to do that AND limit the alternator output to a safe level?

And if the above is not true, how is my system working?

[booster]

Originally Posted by rowiebowie

Still confused. Why is a Balmar and intermediate lead-acid battery necessary to get the proper charging profile to the new lithium coach batteries since it is precisely the job of a DC to DC to do that AND limit the alternator output to a safe level?

And if the above is not true, how is my system working?

IIRC, you have a single alternator so it will activate off the starting battery. A standalone second alternator needs to see a battery to activate so a B to B will not work with them unless you have a way to activate the alternator, like an AGM battery in this case.



A B to B works well and simply with a single alternator or parallel alternators but is more trouble with standalone. A Balmar will also have the same issue is the lithium batteries go offline and removed it's reference from the Balmar.


Of course, if you want fast charging, you can get limited by the capacity of a single alternator, so not much choice about using a second alternator which means no ideal solution unless the vehicle allows the alternators to be run parallel, like out 07 Chevy does and we do. The Transit that Avanti is getting should be OK also because it is a factory controlled second alternator and wouldn't need any separate reference to run.


I like the Balmar mostly for the current limiting and profile, but it will also be considerably more efficient than a B to B would be. It would also be able to give you 300 amps or more if you need/want it.

[rowiebowie]

Originally Posted by booster

IIRC, you have a single alternator so it will activate off the starting battery. A standalone second alternator needs to see a battery to activate so a B to B will not work with them unless you have a way to activate the alternator, like an AGM battery in this case.



A B to B works well and simply with a single alternator or parallel alternators but is more trouble with standalone. A Balmar will also have the same issue is the lithium batteries go offline and removed it's reference from the Balmar.


Of course, if you want fast charging, you can get limited by the capacity of a single alternator, so not much choice about using a second alternator which means no ideal solution unless the vehicle allows the alternators to be run parallel, like out 07 Chevy does and we do. The Transit that Avanti is getting should be OK also because it is a factory controlled second alternator and wouldn't need any separate reference to run.


I like the Balmar mostly for the current limiting and profile, but it will also be considerably more efficient than a B to B would be. It would also be able to give you 300 amps or more if you need/want it.

Ok, but I figured surely there was a better solution than installing another lead-acid battery just to activate a second alternator. Seems like a situation begging for a solution.

[booster]

Originally Posted by rowiebowie

Ok, but I figured surely there was a better solution than installing another lead-acid battery just to activate a second alternator. Seems like a situation begging for a solution.

The only way that I can think of, other than parallel, that would be without an extra battery would be to be able to switch from the second alternator to the main alternator to get the lithium batteries until the come back online or run the heaters if they are in cold shutdown without charging until warm enough.



In the real world, though, it is likely not a big deal as the lithium pack should be online all the time unless you discharge it to far or let it get too cold. If it fails a BMS or something and is dead, you are out of luck anyway. Cold recovery issues are the one we hear the most about, I think, as you need to be able to get the batteries warm somehow if you leaving in the cold and need the power. Being able to at least run the heaters off the main alternator or shore power goes a long ways to solving that.

[GallenH]

Originally Posted by booster

I like the Balmar mostly for the current limiting and profile, but it will also be considerably more efficient than a B to B would be. It would also be able to give you 300 amps or more if you need/want it.

Can B2B chargers have current limiting? I thought I remembered hb7 mentioning dialing back his from 50 to 40A. Or is that not what you're talking about?

How is a Balmar considerably more efficient?

thx.glenn

[booster]

Originally Posted by GallenH

Can B2B chargers have current limiting? I thought I remembered hb7 mentioning dialing back his from 50 to 40A. Or is that not what you're talking about?

How is a Balmar considerably more efficient?

thx.glenn

B to B chargers do current limit, but they are pretty low output and expensive, especially if you need to get two to get capacity. So as I said, for small single alternator system and good option as most are limiting to under 60 amps so they don't overload the alternator. For a bigger system it is much harder to do. I think Sterling has a 120 amp version that is quite pricey.



B to B chargers, per what owners have stated, are about 80% efficient. This would make a 50 amp charge rate pull 60 from the alternator and the 120 amp version pull 144 amps from the alternator. That is quite a bit if you have smaller alternator capacity and you need to dissipate that heat from the B to B wherever you put it.



A Baldor does not do anything high current, it just controls the field of the alternator which is normally a ways under 7 amps. This is just like what the alternator would draw to run an internal regulator. This way the alternator can deliver it's full output to the batteries without any extra loss.

[avanti]

Originally Posted by booster

A Baldor does not do anything high current, it just controls the field of the alternator which is normally a ways under 7 amps. This is just like what the alternator would draw to run an internal regulator. This way the alternator can deliver it's full output to the batteries without any extra loss.

Doesn't that make them in effect 100% efficient (ignoring the trivial power for the logic and the small field current, which is really being consumed by the alternator, not the Balmar)? As you say, the current isn't even passing through the device, so nothing is wasted as heat.

[booster]

Originally Posted by avanti

Doesn't that make them in effect 100% efficient (ignoring the trivial power for the logic and the small field current, which is really being consumed by the alternator, not the Balmar)? As you say, the current isn't even passing through the device, so nothing is wasted as heat.

I would agree they are effectively as efficient as the alternator would be without them and on an internal regulator, and if you are just comparing them to an internally regulated alternator with a B to B on it, we would be looking at essentially 100% vs 80% efficient to the batteries AFAIK.

[GallenH]

OK. I think I understand the efficiency issue. However, for those of us with a standard single alternator, the only option is a B2B, right? Unless we want to add a 2nd alternator and the Balmar at ~$1200, correct?

thx.glenn

[booster]

Originally Posted by GallenH

OK. I think I understand the efficiency issue. However, for those of us with a standard single alternator, the only option is a B2B, right? Unless we want to add a 2nd alternator and the Balmar at ~$1200, correct?

thx.glenn

Yes, as long as you are OK with the reduced charge rates and can spare the amount you need to cover the 20% loss. In marginal alternator size applications you would be way better off in cost and complexity to just put in a higher output alternator in place of the standard one then you can get higher output with a larger B to B with maybe only wiring size changes. Once you get much above 80 amps charging rate, it starts to tilt to using a separate alternator, IMO.


I find it pretty interesting that when lithium batteries were first coming out, one of the biggest advantages they touted were the extremely high charge rates and short charging times compared to lead acid. They were looking for quick recharges for either idling or short drives after running AC all night, I think, as a sales point. They still have the advantage in time to get to totally full from 80% SOC, but the current .4C charge rate that Battleborn wants now (they used to be much higher rate) is just about what most AGMs can accept continuously up to about 75% SOC. We routinely charge our AGMs at 120-180 amps continuously on our 440ah bank. With the high rate charging going away for many moderately priced lithium systems, the low rate single alternator and B to B are getting more common and practical.

[avanti]

Originally Posted by GallenH

OK. I think I understand the efficiency issue. However, for those of us with a standard single alternator, the only option is a B2B, right? Unless we want to add a 2nd alternator and the Balmar at ~$1200, correct?

thx.glenn

Actually, there is a third option, and it is a pretty good one in many cases:

You can use the DC from your engine alternator to power a large inverter (say, 2,000 watts). Use the 120VAC output from this inverter to power the "shore power" input to your coach's charger, which will then charge you battery just as if you were plugged in to shore power, using whatever profile you have programmed. Good chargers let you limit the shore-power takeoff, so you can use this feature to limit the current demanded from your alternator to any level you desire.

This is probably what I am going to do in my new Transit.