another DIY roadtrek lithium - newb needs help

[bumpersignal]

Thanks, booster that was generous for all that insight. However I think for the $130 that the local marine repair shop quoted , it would be worthwhile to have it professionally done.

[bumpersignal]

Originally Posted by booster

When you put on a Balmar it is true that the Balmar is what turns on (excites if you prefer) the alternator, but the Balmar will not do that unless it sees a battery in the system so is really no different than if the regulator is inside the alternator.

Curiously, I was wondering what excites the 2nd alternator in its stock form? My '15 Roadtrek Adventurous came with the 2nd alternator as a standalone for the AGM coach batteries. Since it isn't connected to the starter, what tells the built in internal regulator to excite the alternator to start charging the AGMs?

[larrylwill]

Its connected to the AGM batteries. That's all it needs to work. In my case its connected to the dc2dc converter which has no voltage on its input, so it wont start. If you would remove the battery's from yours it wouldn't work either.

[bumpersignal]

Originally Posted by larrylwill

Its connected to the AGM batteries. That's all it needs to work. In my case its connected to the dc2dc converter which has no voltage on its input, so it wont start. If you would remove the battery's from yours it wouldn't work either.

So as long as there's a battery connected to the alternator, it's always "excited" then? What if I accidentally deplete the lithium and or if BMS shuts off for protection either cold or heat or over voltage

[larrylwill]

Then you cant charge the battery. That's why I added a dc2dc because my generator was putting out 280 amps and the bms was 150A and it would shut down, so it wouldn't charge the battery but adding the dc2dc added more problems than it fixed.
Remember the BMS is to protect the batteries. If it shut down the charging you shouldn't charge the batteries until the temp gets back up or down, or whatever the problem is gets fixed.

[larrylwill]

Guys I have another idea to excite the alternator. I have solar, why cant I connect the solar charger controller output to the dc2dc. Any thoughts?

[GallenH]

I believe that i have a MAJOR misunderstanding here. Are you saying that if I take my old,old RV and take the output of my alternator that goes to my 100AH AGM battery and place a B2B in between the two to get a good charging profile that I will need something to excite the B2B for it to work?

[larrylwill]

Depends. I have 2 alternators, one is dedicated to the house batteries, one is the standard one for starter. Unless you have a newer Rodatrek with Underhood generator or 2nd alternator everything should work correct. In other words if you only have 1 alternator and you connect the dc2dc in series with the house battery, I don't see a problem. If your using only AGM batteries why bother with a dc2dc converter?

[GallenH]

It was always my impression that AGM batteries like to see a charge profile as well and not an "all-out-12+volts-from-the-alternator." IOW: a bulk, absorbtion, and float. Is that incorrect?

[larrylwill]

Don't you have a inverter/charger in the RV? If not, you have the same situation with the starter battery and its been that way for years, the Alternator has a regulator. This thread was about charging Lipo4 batteries.

[GallenH]

No inverter in the RV. Just a charger/DC distribution panel.

So what you're saying is that charging a starter battery is the same as a deep cycle?

No LiPo4 right now. But what if I replace my AGM with a LiPo4? Hence my question in this thread.

[larrylwill]

The battery resistance goes up as it charges and the current it will accept goes down until it stops accepting a charge. So yes. AGM batteries are basically the same as wet cells or gel cells.
https://www.knowyourparts.com/techni...ully%20charged.

[GallenH]

Interesting link. So what does this mean:

You can use your regular battery charger on AGM or gel cell batteries.

False. These batteries like to be charged slow and low. Many AGM/gel cell battery chargers have microprocessors that collect information from the battery and adjust the current and voltage accordingly. Some have different settings for charging flooded, gel and AGM batteries. Overcharging can kill these batteries. Also, alternators are not chargers. Don’t rely on an alternator to do the work of a *charger. If a battery is discharged to the point that it cannot start the vehicle, use a charger as soon as *possible to make sure the battery gets fully charged.

It seems to imply that there are different considerations and this discussion does not address starting vs. deep cycle.

I'm not arguing. Just trying to understand.

thx.glenn

[larrylwill]

You are right but if your RV came with AGM batteries it should have the proper charger or regulator or Inverter/charger. If not you have a other things to. It was my opinion that your RV came with AGM batteries. I do know several people that have changed to AGM's and not changed anything else in there system and have not have any problems. I'm not an expert on AGM or any battery, like most people I try to learn by reading many sources.
I ran my 1993 Roadtrek on standard starter batteries for 10 years before I changed to Marine batteries. I also used a non sinewave inverter for those 10 years. Never had any problems. I never used a AGM until I had a 2014 Roadtrek.

If you check threads you will find some people suggest keeping an AGM on the 2n alternator output. Lots of good/bad/who knows info out there and in here. Especially about lifepo4. I explored paralling a 2nd BMS on my Lifepo4 battery and some people said NO don't do it but Will Prouse tried it without problems.

[GallenH]

Got it. Thanks, larrylwill.

[booster]

Originally Posted by GallenH

I believe that i have a MAJOR misunderstanding here. Are you saying that if I take my old,old RV and take the output of my alternator that goes to my 100AH AGM battery and place a B2B in between the two to get a good charging profile that I will need something to excite the B2B for it to work?

There is getting to be a lot of misunderstanding and mixing up of AGM and lithium systems I think.


There are literally millions of older RVs with AGM batteries running straight from the batteries. Is it the perfect way to do it? No? Can it be made better? Yes but it is not cheap or easy to do really well but can be improved at more moderate costs.


With the AGM batteries, you never have them going offline like you do with lithium so there is no alternator activation issues as it will always see a battery if direct to them or through a B to B if you use one. If you are on a single alternator you will never have any issue even if you disconnect the coach batteries, the alternator will see the starting battery. It is when you go to the standalone second alternator you have issues with activation.



Older vehicles might have alternators that run at only 13.8v so they will undercharge and charge slowly on any lead acid battery. Newer vehicles run closer to 14.1 to 14.5v so are much better as long as you add the ability to shut off the charging when the batteries get full. Overcharging is hard on any battery. Add a battery monitor so you know the AGMs are full and a disconnect to shut off the charging and you have a quite good setup for AGMs if you have the higher voltage alternator. All of this assumes the batteries and alternator are large enough to work well together so you don't need to reduce current. AGMs can absorb about 40 amps per 100ah of capacity so they are rarely the limiting factor once you get to 200ah of capacity continuously and more for shorter times. Wiring and alternator capacity would more commonly be the limit. Only then would you need a B to B or split charge unit that limits amperage to the batteries. Units with a second alternator and a remote regulator can limit the output right with the regulator settings, but that only works for relatively big battery banks as the Balmar can only turn down 50% so about 120 amps hot.


It can get very confusing when talking about litium, AGM, single alternator, dual alternator at the same time.

[bumpersignal]

Thanks for that explanation. In the case of a stand-alone 2nd alternator direct connect to an agm, how does it see the agm when that battery is depleted? What excites that standalone alternator in that use case?

[booster]

Originally Posted by bumpersignal

Thanks for that explanation. In the case of a stand-alone 2nd alternator direct connect to an agm, how does it see the agm when that battery is depleted? What excites that standalone alternator in that use case?

That is the case of why an alternator or charger is not wanted to be running on the battery if it has gone bad or such. If they are the smart versions the alternator and the chargers, b to b, solar, and shore, take a look for a minimum voltage on the battery, not necessarily a good to use voltage. Some also check to see if the battery will accept actual amps, but I think this is a relatively small number. IIRC most them use about 9v or so, so the battery has to be very, very dead. We see a fairly large amount of questions on the forum concerning shore chargers that won't charge because the battery was completely depleted, which is the same issue.


Hitting a dead, and maybe even frozen if it is winter, battery can be a very bad thing that can even rupture the battery case. This used to be very common here in Minnesota in the very cold weather. The battery would be low on charge and freeze, the inexperienced jump truck driver would come and hit it with 300 amps from a jump start generator and the battery would rupture.


In general, you would need to put a relatively low output fixed output non smart charger (Progressive Dynamics shore chargers also work, it appears) on the battery to get it up to voltage so the chargers will kick in. If you have normal single alternator system, you can use the engine running alternator to do that function as is will be activated off the starting battery. If there is a separator you may have to jump around it in many cases as it might not close if it does not see a battery on both sides, just like the chargers. Turning on the heater blower and headlights at idle to reduce the current available for first couple of minutes is not a bad idea, or even just letting the starting battery charge the coach for a bit (risky as you can kill the starting battery and not be able to start if you do that too long or have a bad battery).


All of the issues with activation get magnified when you go to a standalone alternator for the coach and have lithium batteries that can and do shut themselves off. Single alternators are much easier to deal with and that is one of the reasons that when we put on a second alternator we ran it in parallel with an upgraded original. Or van was made just before they went to the computer controlled charging so it doesn't care if the amount of alternator capacity changes. Both alternators run off the same remote regulator the does multistage charging, plus I have a disconnect to the coach when the batteries get full. It is just like have a 530 amp single alternator.

[rowiebowie]

Originally Posted by bumpersignal

So as long as there's a battery connected to the alternator, it's always "excited" then? What if I accidentally deplete the lithium and or if BMS shuts off for protection either cold or heat or over voltage

I once depleated my lithium coach batteries to BMS cutoff. They would no longer charge from an ac source (house current or generator), but charged up just fine from my engine alternator through my Renogy 40A DC to DC charger.

Perhaps the main factor in my situation is the ignition wire that runs to my DC to DC. It is the same one that ran to my original Battery Isolation Manager that is now bypassed as a result of my lithium upgrade. This "ignition wire" is a very small gauge wire, probably only 18ga tops.

[rowiebowie]

Originally Posted by GallenH

I believe that i have a MAJOR misunderstanding here. Are you saying that if I take my old,old RV and take the output of my alternator that goes to my 100AH AGM battery and place a B2B in between the two to get a good charging profile that I will need something to excite the B2B for it to work?

In my case, I needed to only reroute the ignition wire from my old Battery Isolation Manager to my DC-DC charger. SEE BLUE ARROW

When the ignition is on, my alternator charges the lithium batteries. Since I don't always need or want charging, I wired an "ON/OFF" switch on the ignition wire so I can turn it on only when needed.

My original Battery Isolation Manager remains in place, but now completely bypassed due to my lithium battery & charging upgrades. Three years now and all working great.