lithium conversion questions

[tombuchanan]

I have a 2017 sunseeker by forest river class C rv. I just bought 2 100mah renogy lithium iron phospate batteries to replace my flooded lead acid. I've been doing a lot of researching figuring out what I need to change. My stock inverter doesn't have a switch to flip for lithium batteries so I understand it will not charge these lithiums to their full capacity and I can be ok with that. I guess my bigger concern is charging from the alternator. I'm a little reluctant to hook the batteries up at this point so I measure right now about 13 volts coming from the converter and about 14.1 coming from the alternator. These lines are normally both connected to the battery so I was wondering if that's normal that both the house inverter and the alternator both have live connections to the battery at the same time. My bigger concern is that I've heard the alternator can be damaged without a dc to dc charger in between since having 200mah of lithium can draw too much current. So then do I just put this dc to dc charge in between the old alternator supply line and the battery since this will be supplying 14.6 to the battery while the house inverter is still pushing 13. Any help would be appreciated.

 

[Mark_K5LXP]

The issue isn't so much the voltage of the alternator, it's actually about right to charge lithium. The problem is current - a discharged lithium will draw large currents from the alternator for a relatively long period of time, longer than some alternators can supply without overheating. A DC-DC converter made for this purpose will limit the current from the alternator to a "safe" level, say 30 amps. The battery still gets a useful charge rate and there is now plenty of power headroom for the alternator to do other alternator things. Nothing says you have to use this source if you don't want to, maybe shore, genset or solar power is all you really need. Or just get the DC-DC converter and check the box.

Mark B.
Albuquerque, NM

 

[Isaac-1]

You mention having both a converter and an inverter with a charger, it is not common to have both types of devices installed on the same battery bank. Can you tell us the exact brand and models of equipment you are dealing with, so we can have a better picture of the situation.

p.s. depending on the charge profile / profiles of the charger it may work fine with LiFePo4 batteries even without a dedicated Lithium charging mode.

 

[Lou Schneider]

I took your mention of a stock inverter to mean a stock converter instead, i.e. you only have one charger along with the engine alternator. Correct?

A DC to DC converter can boost the voltage as well as limit the current going to the batteries so with a little creative wiring it can solve both problems.

Disconnect the stock converter from the fuse board so the board is fed only from the batteries. Run a new line from the converter's output to the input of the DC to DC converter and connect it there along with the charging line from the vehicle's alternator. Take the output of the DC-DC converter to the batteries. The DC to DC converter will boost the voltage from your stock converter as well as limit the current when the alternator is running. It's OK to connect two DC sources together, the one with higher voltage will simply block the current from the one with lower voltage. It's AC where you can't connect two sources together without special precautions.

 

[Gary RV_Wizard]

You mention having both a converter and an inverter with a charger, it is not common to have both types of devices installed on the same battery bank.

Actually, it is the norm in any motorhome. But mostly they are not active at the same time unless the generator is running while the coach is being driven. Otherwise, the house charger operates when on shore or generator power and the alternator while the engine is running. It's not a problem in any case - the higher voltage source dominates. The same applies if solar charging is installed.

 

[ButchW]

I took your mention of a stock inverter to mean a stock converter instead, i.e. you only have one charger along with the engine alternator. Correct?

A DC to DC converter can boost the voltage as well as limit the current going to the batteries so with a little creative wiring it can solve both problems.

Disconnect the stock converter from the fuse board so the board is fed only from the batteries. Run a new line from the converter's output to the input of the DC to DC converter and connect it there along with the charging line from the vehicle's alternator. Take the output of the DC-DC converter to the batteries. The DC to DC converter will boost the voltage from your stock converter as well as limit the current when the alternator is running. It's OK to connect two DC sources together, the one with higher voltage will simply block the current from the one with lower voltage. It's AC where you can't connect two sources together without special precautions.

I'm assuming these are only coach batteries... Is the chassis battery still a flooded lead acid battery? If so, Lou how would you wire it so that you could charge the chassis battery off the generator or shore power, as well as from the alternator?
Butch

 

[Gary RV_Wizard]

how would you wire it so that you could charge the chassis battery off the generator or shore power, as well as from the alternator?

That function is common on Fleetwood and later model Winnebago motorhomes. There are devices made to "smart" manage this, e.g. the LSL Trik-L-Charge, Intellitec BCC, Xantrex Echo Charger or Magnum Combiner. Basically a relay that gets closed to cross-connect the house positive to the chassis positive when the house charger is active and has capacity to spare, e.g. wafter the house battery bank reaches full charge. The alternator is always connected to the chassis battery, but the house charger only as needed.

 

[ButchW]

That function is common on Fleetwood and later model Winnebago motorhomes. There are devices made to "smart" manage this, e.g. the LSL Trik-L-Charge, Intellitec BCC, Xantrex Echo Charger or Magnum Combiner. Basically a relay that gets closed to cross-connect the house positive to the chassis positive when the house charger is active and has capacity to spare, e.g. wafter the house battery bank reaches full charge. The alternator is always connected to the chassis battery, but the house charger only as needed.

Then you would install the DC-DC converter AFTER the connection to the chassis battery (So as to not over charge the chassis battery with the higher voltage)?
Butch

 

[Lou Schneider]

Then you would install the DC-DC converter AFTER the connection to the chassis battery (So as to not over charge the chassis battery with the higher voltage)?
Butch

The DC to DC converter only feeds the lithium house batteries, the alternator continues charging the chassis battery the way it always has. So yes, it goes after the point where the chassis battery is connected to the alternator.

One disadvantage to installing a DC to DC converter is it doesn't let current flow backwards through it, so you won't be able to use a Boost switch to let the house batteries jump start a low starting battery.

 

[tombuchanan]

awesome information, I never would have thought to connect the house converter into the dc to dc since should also bump the voltage up to what lithium can take. The chassis battery is a flooded acid. the house converter is a 110169j from progressive dynamics. I've enclosed the diagram showing my setup. I'm a little unsure of where to disconnect the stock converter. The 110169j which I believe is the stock converter you're talking about is connected to the breaker panel under the master bed. Or did you mean at this fuse panel that the picture shows which is located right next to the battery bank?

 

[tombuchanan]

The DC to DC converter only feeds the lithium house batteries, the alternator continues charging the chassis battery the way it always has. So yes, it goes after the point where the chassis battery is connected to the alternator.

One disadvantage to installing a DC to DC converter is it doesn't let current flow backwards through it, so you won't be able to use a Boost switch to let the house batteries jump start a low starting battery.

that's fine, i have a long pair of jumper cables that will reach

 

[Isaac-1]

Actually, it is the norm in any motorhome. But mostly they are not active at the same time unless the generator is running while the coach is being driven. Otherwise, the house charger operates when on shore or generator power and the alternator while the engine is running. It's not a problem in any case - the higher voltage source dominates. The same applies if solar charging is installed.

Gary I think there was some mis-communication here, I read the OP post as suggesting that the motorhome has an inverter/charger as well as a converter, both of which would charge the house batteries from shore power, as well as an alternator that would charge it while the engine is running. At one point also saying that their was not a lithium charge profile, but not mentioning the brand and model of the unit.

Also there is some incomplete information in the replies above, like saying that a DC-DC charger would prevent the main converter from also keeping the chassis battery charged. This may or may not be true as at least some DC-DC chargers will also provide a charging feature for the chassis battery when there is excess charge available. See the Renogy DCC50S like I own as an example, it integrated a DC-DC charger, chassis battery charger and solar MPPT solar controller all into one unit.

 

[Lou Schneider]

awesome information, I never would have thought to connect the house converter into the dc to dc since should also bump the voltage up to what lithium can take. The chassis battery is a flooded acid. the house converter is a 110169j from progressive dynamics. I've enclosed the diagram showing my setup. I'm a little unsure of where to disconnect the stock converter. The 110169j which I believe is the stock converter you're talking about is connected to the breaker panel under the master bed. Or did you mean at this fuse panel that the picture shows which is located right next to the battery bank?

Disconnect it at the Converter terminal on the panel you show so only the batteries feed the panel. Then extend the output of the converter to the input of the DC to DC converter.

 

[John From Detroit]

There is a simple solution.. for battery charging via the alternator.
Replace the isolator with a Solar Charge Controller
(The danger here is you lose the ability of the House to charge the chassis battery less you Trick-L-Start it) Now the current and voltage are both controlled by the Charge Controller.

Same for the house converter by the way.. Feed it to a Solar Charge controller than to the battery.. This may require relocation or re-wiring.

WILL NOT WORK WITH AN INVERTER/Charger Only with a stand alone converter.

NOTE some Solar controllers can boost.. Some can not. .

 

[tombuchanan]

ok, that makes sense. any advice on a good dc to dc converter. I've been looking at the renogy 40 amp (B07Q4SVX3M).

 

[Gary RV_Wizard]

Gary I think there was some mis-communication here, I read the OP post as suggesting that the motorhome has an inverter/charger as well as a converter, both of which would charge the house batteries from shore power, as well as an alternator that would charge it while the engine is running. At one point also saying that their was not a lithium charge profile, but not mentioning the brand and model of the unit.

OK, but that wouldn't really change anything. It's quite normal to have multiple charging sources active at times and ok to do so. Solar, converter/charger, inverter/charger, alternator, whatever.

 

[tombuchanan]

There is a simple solution.. for battery charging via the alternator.
Replace the isolator with a Solar Charge Controller
(The danger here is you lose the ability of the House to charge the chassis battery less you Trick-L-Start it) Now the current and voltage are both controlled by the Charge Controller.

Same for the house converter by the way.. Feed it to a Solar Charge controller than to the battery.. This may require relocation or re-wiring.

WILL NOT WORK WITH AN INVERTER/Charger Only with a stand alone converter.

NOTE some Solar controllers can boost.. Some can not. .

what do you think is the advantage of using a solar charge controller instead of a dc to dc converter? I guess I don't know what the difference is.

 

[Contributor]

Depending on the Amp rating of the alternator, you may be ok without the DC-DC converter. Here is a good real world example of a guy who really did his homework. He also added a switch to disconnect the alternator from the system when he wished. I liked his video.

Notice that his battery bank was 400Ah LiFePO, twice the OP's 200Ah.

 

[John From Detroit]

what do you think is the advantage of using a solar charge controller instead of a dc to dc converter? I guess I don't know what the difference is.

Charge controllers are "Smart" compared to a DC/DC Buck/Boost converter. But basicaly an MPPT controller is DC/DC converter. with added featuires as I understand them.

However you'd' want to check that out.

 

[Lou Schneider]

Charge controllers are "Smart" compared to a DC/DC Buck/Boost converter. But basicaly an MPPT controller is DC/DC converter. with added featuires as I understand them.

However you'd' want to check that out.

You've mentioned using a MPPT solar charge controller with an alternator several times, John. This is the wrong application for it and it will likely damage the controller if you use it to regulate an alternator's output.

MPPT solar controllers are designed to function with solar panels where the current is not much greater into a short circuit (Isc) than at the panel's Maximum Power Point (MPPT). These are both specifications that are stated on the panel so you can choose an appropriate controller.

Alternators don't act this way, they deliver essentially unlimited current into a short circuit. A MPPT controller has a specified maximum input current limit and it can be damaged if you ask it to regulate the virtually unlimited output current of an alternator.

And a MPPT controller only reduces the input voltage as it converts the excess voltage into additional current. It does not transform a low input voltage into a higher output voltage the way a DC-DC converter will.