Lithium safe converter

[Jims94vmx]

Jims94vmx,

You will want to be sure to use a DC DC charger such as the Renogy like Howard, I and others are using for Lithium RV batteries connected to the TV. Your question on the load still being applied to the vehicles alternator is valid. This is why its best to activate the charger with the RV lights. This is what Renogy refers to the D+ circuit. This way, you can turn on the lights when underway and avoid added the load to the alternator when at idle. For those that are traveling at night, it may be best to leave the Truck/RV lights off until pulling away from the campsite. This will allow some time to warm the engine a bit, and to give the alternator time to recover the lost energy from cranking the engine. I'm stating this since vehicle systems can vary by large margins and have almost infinite features such as heated seats, and other high load items. While alternators are smart systems today, they are calibrated by humans which most likely are not doing this while connected to an RV Lithium battery. Eventually everyone will consider the increasing use of Lithium batteries in their RV and at some time in the future, we will see them in the TV as well.

Jim

Thanks Jim......Jim

[Jims94vmx]

I completely understand. My journey from stock OEM to where I am now has been an almost two year odyssey. Take your time and-please--ask questions. There's a wealth of information and individuals here who can help.

If you really want to "overload" (!), look at this one: https://gdrvowners.com/forum/operati...lts-f-350-mods

Thanks Howard. Looking, learning and will be asking.....

[Jims94vmx]

Anyone using the Renogy 50 amp DC to DC with mppt controller. That looks like a great way to jump in....?

[Running from Gnats]

Excuse me, but I'm confused. My 2019 F-150 has a 25 amp fuse on the 12v circuit feed from the truck to the trailer. Since the fuse would blow, exactly how would using lithium batteries (I have 2 Lion Energy) burn out the alternator. With the fuse out of the circuit (blown or removed) the 12 volt feed is cut off and the batteries would not be drawing from the alternator. Besides, with 200watts of DC, a day's travel won't come near running down the batteries.

[howson]

Guest -- it isn't clear in post #34 whom Running from Gnats is addressing with the question (maybe no one in particular) so leaving the response to you as one of our foremost truck experts.

Howard

[Running from Gnats]

Good morning. I called Lion Energy this morning and asked them about charging with my TV. There response was, "We don't recommend it. You may get by with it a few times but eventually you will damage your alternator. We recommend using a Redarc 1225d or something similar. We don't recommend charging lithium batteries without a DC to DC charger."

Now what? I'm not as concerned about charging the battery while driving. I just don't want to cause damage.
I'm not sure. Conflicting information on the net. Below is a screenshot from Progressive Dynamics.
Thanks
Dennis

This is one of the reasons I'm confused. Modern vehicles are fuse protected, so if your vehicle is fused for 25 amps, why does Lion Energy and Battle Born say the alternator is at risk if you don't use a DC-DC charger. Is this a case of old knowledge and an attempt to KYA if their battery electronics fails? As an FYI, the alternator is rated at 200 amps, the trailer 12v feed is 25 amp, and I have a small 12v backup battery for the trailer emergency brakes.

I'd really like an explanation as to how a lithium battery can burn out an alternator which is fuse protected. Ford says if the batteries try to pull high amps, the fuse blows and the connection is gone. That is from Ford engineering and my dealer electronics tech (20 years as an military aircraft electronic lead tech).

[Cate&Rob]

I'd really like an explanation as to how a lithium battery can burn out an alternator which is fuse protected.

An excellent question . . . I would like to learn this too.

Rob

[Guest]

This is one of the reasons I'm confused. Modern vehicles are fuse protected, so if your vehicle is fused for 25 amps, why does Lion Energy and Battle Born say the alternator is at risk if you don't use a DC-DC charger. Is this a case of old knowledge and an attempt to KYA? As an FYI, the alternator is rated at 200 amps, the trailer 12v feed is 25 amp, and I have a small 12v backup battery for the trailer emergency brakes.

I'd really like an explanation as to how a lithium battery can burn out an alternator which is fuse protected.

Running from Gnats,

I've been looking into this and while a 25amp load is small the lithium battery is capable of pulling much more than 25 amps so the fuse may blow if the SOC (state of charge) of the battery is low enough. Once the fuse is blown and the circuit is open, there is no risk to the alternator since there would be no additional load applied. For direct connecting to the TV battery, the lithium battery can draw excessive current which can put undo stress on the alternator without an intermediary device such as a DC DC charger.
So It's best to use a DC DC charger with a lithium battery for two reasons.

1) The charger controls how much load is being applied to the TV charging system. In the case of my Renogy 20amp unit, maybe 25amps.
2) The DC DC charger has its own charge profile for the lithium battery where it will stop the charge so we do not need to rely on the battery BMS to do so. I like the redundancy in doing this.

For using the DC DC charger, I believe there is much lower risk as directly connecting the trailer battery to the TV, but I believe there may still be some concern since the DC DC charger is still not part of the vehicle control system. For the following scenario. If the trailer battery and the TV battery would be low, the TV control system will attempt to bring the battery up to a reasonable SOC. If excessively low the system may turn off some components which is called load shedding. But if demand is high enough and the TV battery still needs help, the system will attempt to bring the TV battery up where the DC DC charger will continue to draw and cannot be turned off by the TV control system. Since the size of the TV charging system, the amount of electrical loads applied from initial start up, heated seats, heated steering wheel and much more, plus the size of the DC DC charger its impossible to determine if we are applying too much load to the alternator at sustained idle.

As a result, it may be best to connect the ignition circuit or activation circuit of the DC DC charger to the camper marker lights or to a manual switch. This way after the initial start up of the vehicle the DC DC can be activated after the charging system has recovered from the initial starting of the TV. Just before travel the DC DC charger can be activated where RPM will be up and cooling of the alternator will not be a concern.

I hope this helps,

Jim

[Country Campers]

Running from Gnats

I think the majority of the DC to DC discussion stems from some only getting a small amount of amps from the trailer wire , 5 or 10 amps maybe. I believe here is why some have sent straight to the battery to power and charge the trailer batteries when traveling. Going straight to the battery eliminates the 25 amp fuse that you are mentioning. This also , as Jim has stated above , may put undo stress on the tow vehicle battery and charging system but would result in more amps flowing to the trailer battery bank and thus needing the DC to DC charger to monitor trailer battery charging.
If you are only using battery power from the trailer to truck cord then yes this would be fused as you have stated and yes if there is an overdraw condition and the fuse blows it will cut power to the trailer and not harm the truck charging system ( I think).

Brian

[ncitro]

Running from Gnats

I think the majority of the DC to DC discussion stems from some only getting a small amount of amps from the trailer wire , 5 or 10 amps maybe. I believe here is why some have sent straight to the battery to power and charge the trailer batteries when traveling. Going straight to the battery eliminates the 25 amp fuse that you are mentioning. This also , as Jim has stated above , may put undo stress on the tow vehicle battery and charging system but would result in more amps flowing to the trailer battery bank and thus needing the DC to DC charger to monitor trailer battery charging.
If you are only using battery power from the trailer to truck cord then yes this would be fused as you have stated and yes if there is an overdraw condition and the fuse blows it will cut power to the trailer and not harm the truck charging system ( I think).

Brian

I think this is exactly right. Before there were lithium batteries, when people wanted more charge out of their truck they would run some large wires from the truck battery to the rv battery. I think that’s what the battery manufacturers are trying to warn against. I have four Lion batteries and about 20,000 miles on them last year with the seven pin doing charging and sometimes the batteries at a very low SOC. I never popped my fuse or had a problem.

That said I’m starting the 40 amp Renogy Charger project, waiting on parts (things don’t come near as fast in this Covid world) mainly for increased charging capacity.

[Cate&Rob]

some only getting a small amount of amps from the trailer wire , 5 or 10 amps maybe.

This is an observation made by several owners, in a discussion quite a while ago. There seems to be something in the TV circuitry that limits output to the trailer battery to far less than what the circuit is fused for. This is the situation with my TV, even when the trailer battery is significantly discharged and should be able to take a greater charge rate.

Rob

[Guest]

This is an observation made by several owners, in a discussion quite a while ago. There seems to be something in the TV circuitry that limits output to the trailer battery to far less than what the circuit is fused for. This is the situation with my TV, even when the trailer battery is significantly discharged and should be able to take a greater charge rate.

Rob

Rob,

For lead acid batteries this is due to the internal resistance of the battery and the size of the wire on the TV trailer harness. The lithium battery has much lower internal resistance. Thinking the wire size on the 7 pin trailer harness may prevent the fuse from blowing where some trucks have higher capability than others. Also every truck is not wired exactly the same. My 7 pin connector is fused at 35amps, where I'm being conservative in connecting a 20amp Renogy to the battery feed on my 7 pin battery circuit. Trying to avoid a dedicated set of heavy wiring.

Jim

[howson]

Rob,

For lead acid batteries this is due to the internal resistance of the battery and the size of the wire on the TV trailer harness. The lithium battery has much lower internal resistance. Thinking the wire size on the 7 pin trailer harness may prevent the fuse from blowing where some trucks have higher capability than others. Also every truck is not wired exactly the same. My 7 pin connector is fused at 35amps, where I'm being conservative in connecting a 20amp Renogy to the battery feed on my 7 pin battery circuit. Trying to avoid a dedicated set of heavy wiring.

Jim

Jim,
The battery technology is apparently not the only limitation because my '17 Ford F-350, regardless of how much amperage the Battle Borns will accept, would not provide more than ~9 amps in any scenario to the trailer through the 7-pin harness (stock configuration wiring). (I've seen >135 amps when connected to shore power in BULK mode.) This is all documented here (and cross-checks with what TucsonJim experienced with his Ford truck): https://gdrvowners.com/forum/operati...=9189#post9189

Thus why I went with the separate Renogy 40A DC-DC Charger. Again, all documented in the "Tapping 12v...thread". (I know you know, Jim, referencing for other readers.)

I completely understand why you're going the 20A route. I added this clarification(?) so the readers here don't "assume" their 7-pin will provide more amperage based on the type of battery in their trailer.

Howard

[Cate&Rob]

Guest howson
Jim & Howard:

I think Jim may be correct on the wire gauge being the throttle/bottleneck on reaching anywhere close to fuse rating on charging the trailer battery from the TV alternator. This wire is the largest in the harness on both the truck and trailer side of the umbilical connector, but is still only 12 ga at best. Definitely not 10 ga. So . . . from the ABYC chart, a 12 ga wire can barely carry 10 amps for 15 ft with a 3% voltage drop. This would explain why many of us have seen less than 10A from the TV to the trailer battery regardless of the demand from that battery.

Rob

[Guest]

Thanks Guys,

It will be interesting to see what the 20amp Renogy will do while connected to my 7 pin connector. Its fused to 35amps. I'm getting close to installing the battery and chargers but its going to be a deep freeze in Michigan tomorrow night. And I de-winterized. LOL.
Honestly even if I only obtain 10 amps I would still be ok since my goal is to be able to control the charge rather than to rely on the battery BMS. I trust the BMS but like the idea of using it as a redundant system. Something else that I did not mention is how the TV can sometimes exhibit voltages over the 14.6V maximum for lithium charging and is another reason for the charger.......to keep the peak voltage to the battery at the 14.1V setting I am using.

Jim