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 > LiFePo battery upgrade question

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StirCrazy

Kamloops, BC, Canada

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Posted: 11/08/21 07:19pm Link  |  Quote  |  Print  |  Notify Moderator

Teleman wrote:

Since both my staring and house batteries are under the hood I need to figure out where to mount the DC to DC chager.


get a remote thermoniter and put it in the battery location and see how hot it actualy gets there, stop and go trafic in the summer will probably be the hottest. if it is in a location that stays cool then your fine, but most wont. the house battery isnt a big deal to move, its just runing wires from the under hood location to the new location. with the LFP you dont have to worry about spills or off gasing so you can put them anywhere. your DC to DC charger you want as close to the batteries as possible. and even in the situation where you cant move them it might be fine with a simple heat shield as in reality are you using the house batteries while your travleing?

Steve


2014 F350 6.7 Platinum
2016 Cougar 330RBK

Teleman

Clayton, CA, USA

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Posted: 11/08/21 07:56pm Link  |  Quote  |  Print  |  Notify Moderator

otrfun wrote:

Teleman wrote:

otrfun wrote:

Teleman wrote:

I ordered a 200AH LifePo battery to replace my two 100AH lead acid batteries and also a compatabile converter which takes care of charging the battery with shore or generator power but what about charging the battery with the alternator? Does the battery's BMS take care of everything and therefore no need to change or upgrade the alternator? Sorry if this is a dumb question!
A BMS is not designed to function as a charger. It is designed as final line of defense to protect the battery.

If you're counting on the wiring to/from the alternator to limit current between your alternator and batteries, you're going to have to choose the proper gauge wire or cable. Too big (physically), may allow excessive current (potentially overloading both the alternator and/or battery). Too little current will result in excessive charge times. There's no magical chart that's going to give you a precise answer. If you've priced copper wire lately, a trial and error approach could get very expensive. Also, if you change size/type of batteries in the future, you'll need to current match the wiring again.

That's one of the upsides to using a dc to dc charger. It will limit current to a precise amount. Sized properly, you're never in danger of overloading your alternator, plus it will properly charge your lifepo4 by precisely controlling the voltage applied to the battery. IMO $200-$300 for a dc to dc charger is a good insurance to protect both your motorhome and battery.

As for using a fuse as an alternator/battery current limiting device, that's not recommended. Fuses are very inexact devices. Some fuses can allow up to twice their current rating before they open. Fuses are primarily designed to protect in the event of a direct short.

What should I be looking for in a DC to DC charger given a 124A alternator and a 200AH lithium battery? I suppose it's possible I may add a second battery in the future as my motorhomes has space for two.
I think pianotuna has been giving you some solid advice. I'd have to agree with his choice of a 20a dc to dc charger to use with his alternator which he described as similar to yours.

Since you're going with a 40a, it's important to keep the voltage drop between the battery/alternator and your dc to dc charger to an absolute minimum (a voltage drop calculator can help determine the proper gauge wire/cable to use). Any significant voltage drop can push the input current to a 40a dc to dc charger as high as 60a. IMO, 60a is way too much load for a 124a alternator--especially if you have a scenario where you have discharged engine and house batteries, headlights on, a/c on, etc. all at the same time. FWIW, the 20a dc to dc charger under the same max load scenario would draw 30a. If you do run into problems with your 40a you do have the option (as pianotuna also mentioned) of resetting a dip-switch on the outside case to drop it into half-power mode so it will operate just like the 20a Renogy.

Lastly, keep in mind the Renogy is not a sealed unit. It has a couple cooling fans that force air (along with any dust and dirt) inside the case. If you mount the dc to dc charger inside a dusty engine compartment this is something to be aware of (along with any water intrusion issues). FWIW, we mounted 40a our dc to dc charger (truck has a 220a alternator) inside our truck camper and made a ~20 ft 2-gauge run from our truck's battery terminals to the dc to dc charger located inside the truck camper. With 40a of charge current we only experience a 43.5a load on the alternator. Larger (physical size) wires/cables decrease the load on the alternator (decreased voltage drop) while still maintaining 40a of charge current.

Good luck with your install!

If I can mount it in a plastic box safely I can keep the wires really short, 12-18", as the starter and house batteries are located very close to each other under the hood. Renogy recommendso 6ga from the starter battery up to 8' and a 60a fuse, and 8ga and a 50a fuse to the house battery.

pianotuna

Regina, SK, Canada

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Posted: 11/08/21 09:41pm Link  |  Quote  |  Print  |  Notify Moderator

The purpose of the bypass switch.

Scenario.

You are not on shore power. There is no sun for solar. You want to charge the house batteries. The dc to DC renogy fails.

So use the bypass switch to do some charging.

Other advice:

Once you have the dc to DC installed, use a DC clamp on ammeter to check the current. If it is more than 50 amps, pull the "jumper" out of the renogy to limit it to 20 amps.

Input of the dc to DC can be 50% more than the output. So 40 amps out may equal 60 amps in. My opinion is that is far too much for a 124 amp alternator--unless the duty rating is 100% (they rarely are).


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

otrfun

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Posted: 11/08/21 09:52pm Link  |  Quote  |  Print  |  Notify Moderator

Teleman wrote:

otrfun wrote:

Teleman wrote:

otrfun wrote:

Teleman wrote:

I ordered a 200AH LifePo battery to replace my two 100AH lead acid batteries and also a compatabile converter which takes care of charging the battery with shore or generator power but what about charging the battery with the alternator? Does the battery's BMS take care of everything and therefore no need to change or upgrade the alternator? Sorry if this is a dumb question!
A BMS is not designed to function as a charger. It is designed as final line of defense to protect the battery.

If you're counting on the wiring to/from the alternator to limit current between your alternator and batteries, you're going to have to choose the proper gauge wire or cable. Too big (physically), may allow excessive current (potentially overloading both the alternator and/or battery). Too little current will result in excessive charge times. There's no magical chart that's going to give you a precise answer. If you've priced copper wire lately, a trial and error approach could get very expensive. Also, if you change size/type of batteries in the future, you'll need to current match the wiring again.

That's one of the upsides to using a dc to dc charger. It will limit current to a precise amount. Sized properly, you're never in danger of overloading your alternator, plus it will properly charge your lifepo4 by precisely controlling the voltage applied to the battery. IMO $200-$300 for a dc to dc charger is a good insurance to protect both your motorhome and battery.

As for using a fuse as an alternator/battery current limiting device, that's not recommended. Fuses are very inexact devices. Some fuses can allow up to twice their current rating before they open. Fuses are primarily designed to protect in the event of a direct short.

What should I be looking for in a DC to DC charger given a 124A alternator and a 200AH lithium battery? I suppose it's possible I may add a second battery in the future as my motorhomes has space for two.
I think pianotuna has been giving you some solid advice. I'd have to agree with his choice of a 20a dc to dc charger to use with his alternator which he described as similar to yours.

Since you're going with a 40a, it's important to keep the voltage drop between the battery/alternator and your dc to dc charger to an absolute minimum (a voltage drop calculator can help determine the proper gauge wire/cable to use). Any significant voltage drop can push the input current to a 40a dc to dc charger as high as 60a. IMO, 60a is way too much load for a 124a alternator--especially if you have a scenario where you have discharged engine and house batteries, headlights on, a/c on, etc. all at the same time. FWIW, the 20a dc to dc charger under the same max load scenario would draw 30a. If you do run into problems with your 40a you do have the option (as pianotuna also mentioned) of resetting a dip-switch on the outside case to drop it into half-power mode so it will operate just like the 20a Renogy.

Lastly, keep in mind the Renogy is not a sealed unit. It has a couple cooling fans that force air (along with any dust and dirt) inside the case. If you mount the dc to dc charger inside a dusty engine compartment this is something to be aware of (along with any water intrusion issues). FWIW, we mounted 40a our dc to dc charger (truck has a 220a alternator) inside our truck camper and made a ~20 ft 2-gauge run from our truck's battery terminals to the dc to dc charger located inside the truck camper. With 40a of charge current we only experience a 43.5a load on the alternator. Larger (physical size) wires/cables decrease the load on the alternator (decreased voltage drop) while still maintaining 40a of charge current.

Good luck with your install!

If I can mount it in a plastic box safely I can keep the wires really short, 12-18", as the starter and house batteries are located very close to each other under the hood. Renogy recommendso 6ga from the starter battery up to 8' and a 60a fuse, and 8ga and a 50a fuse to the house battery.
The 40a Renogy's case gets very warm plus the two fans will activate whenever it's producing its rated 40a of charge current for any length of time. If you install it inside a plastic box I'd make sure it's well ventilated.

A 2ft long 6 gauge cable run will net you an extremely low .6% voltage drop at 45a. IMO, anything less than 2% is excellent. If you keep your voltage drop on the input at <2% you should easily see less than a 45a load on the input (with 40a on the output).

As for your output, 8 gauge will net you less than a 2% voltage drop at 40a as long as it's less than 5ft.

We followed Renogy's fusing recommendation (60a input, 50a output).

Good luck!

pianotuna

Regina, SK, Canada

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Posted: 11/08/21 09:55pm Link  |  Quote  |  Print  |  Notify Moderator

Teleman wrote:

If I can mount it in a plastic box safely I can keep the wires really short, 12-18", as the starter and house batteries are located very close to each other under the hood. Renogy recommendso 6ga from the starter battery up to 8' and a 60a fuse, and 8ga and a 50a fuse to the house battery.


If there is room--use a plastic battery box to hold the renogy. Make sure there is plenty of ventilation. dc to DC are not wonderfully efficient so the unit may need to dissipate over 250 watts of heat.

One minor concern. Is the starter battery flooded? If so the renogy should not be in the same compartment (corrosion will eat the renogy up). If the starter is AGM, then that's ok for the renogy to be in the same compartment.

I use auto reset circuit breakers rather than fuses.

I have dual 50amp charging paths (an attempt to improve charging before dc to DC devices were available). I've seen 70 amps--back in the old days when I had flooded house batteries (975 amp hours). I would use my inverter while running down the road and turn on the water heater. I used a duty cycle of 20 minutes on and 40 minutes off. I have manual control over the isolation solenoids.

Teleman

Clayton, CA, USA

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Posted: 11/08/21 10:16pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks for all the helpful advice. I'll be sure to use adequate wire, proper fuses or circuit breakers, and make sure the charger is ventilated and protected.

Teleman

Clayton, CA, USA

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Posted: 11/09/21 05:06pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Teleman wrote:

If I can mount it in a plastic box safely I can keep the wires really short, 12-18", as the starter and house batteries are located very close to each other under the hood. Renogy recommendso 6ga from the starter battery up to 8' and a 60a fuse, and 8ga and a 50a fuse to the house battery.


If there is room--use a plastic battery box to hold the renogy. Make sure there is plenty of ventilation. dc to DC are not wonderfully efficient so the unit may need to dissipate over 250 watts of heat.

One minor concern. Is the starter battery flooded? If so the renogy should not be in the same compartment (corrosion will eat the renogy up). If the starter is AGM, then that's ok for the renogy to be in the same compartment.

I use auto reset circuit breakers rather than fuses.

I have dual 50amp charging paths (an attempt to improve charging before dc to DC devices were available). I've seen 70 amps--back in the old days when I had flooded house batteries (975 amp hours). I would use my inverter while running down the road and turn on the water heater. I used a duty cycle of 20 minutes on and 40 minutes off. I have manual control over the isolation solenoids.

Can you recommend or share links to the circuit breakers? I need a 60a and 50a. Thanks!

pianotuna

Regina, SK, Canada

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Posted: 11/09/21 06:26pm Link  |  Quote  |  Print  |  Notify Moderator

Teleman wrote:


Can you recommend or share links to the circuit breakers? I need a 60a and 50a. Thanks!


[image]

https://www.amazon.ca/MASO-Waterproof-Ci........=9001253&hvtargid=pla-625164164044&psc=1

https://www.walmart.ca/en/ip/Circuit-Bre........D5LNGmrdByXRBRoCpNMQAvD_BwE&gclsrc=aw.ds

pianotuna

Regina, SK, Canada

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Posted: 11/09/21 06:29pm Link  |  Quote  |  Print  |  Notify Moderator

I did not use the above--my cousin had 50 amp ones available.

Teleman

Clayton, CA, USA

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Posted: 11/13/21 08:39pm Link  |  Quote  |  Print  |  Notify Moderator

After having the chance to investigate further I decided to return the Renogy unit and bite the bullet and get a Redarc 40A waterproof charger. It's $320 more but it's really the best solution. Trying to figure out a way to keep the Renogy dry was pretty much impossible without moving it to a basement. This way I can place it right next to the house battery and only a few feet from the starting battery. It also has a solar input with an MPPT regulator so when I add solar panels eventually I won't have the added expense of one.

* This post was edited 11/13/21 09:17pm by Teleman *

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