RV.Net Open Roads Forum: Tech Issues: LiFePo battery upgrade question

RV Blog

  |  

RV Sales

  |  

Campgrounds

  |  

RV Parks

  |  

RV Club

  |  

RV Buyers Guide

  |  

Roadside Assistance

  |  

Extended Service Plan

  |  

RV Travel Assistance

  |  

RV Credit Card

  |  

RV Loans

Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tech Issues

Open Roads Forum  >  Tech Issues

 > LiFePo battery upgrade question

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 6  
Prev  |  Next
Sponsored By:
Teleman

Clayton, CA, USA

Senior Member

Joined: 08/11/2004

View Profile


Offline
Posted: 11/08/21 10:10am Link  |  Quote  |  Print  |  Notify Moderator

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

otrfun

On The Road

Senior Member

Joined: 09/08/2012

View Profile



Good Sam RV Club Member


Posted: 11/08/21 10:54am Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:

otrfun wrote:

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.
Fusing as a "current limiting device" on a regular basis is a wrong application for a fuse.

However, it IS recommended to ALWAYS include a fuse, fusable link or circuit breaker in all power sources wiring especially when dealing with high amperage sources.

The fuse/fusable link or circuit breaker is there to protect your wiring in case of catastrophic short on the wiring.

Fuses/fusable links or breakers do not have to be "precise" and there are different types which have intentional delays for specific types of loads. But even so, are there to protect your wiring from getting hot enough to melt wire insulation and cause fires.
The gist of my comment was to acknowledge a fuses lack of precision. Nothing more, nothing less. *If* a given 60a fuse would precisely open at 61a, then, yes, it could be effectively used for current limiting purposes (i.e., protect an alternator from excess battery charge current). Unfortunately, this is not the case. Given batch of 60a fuses of the same type and rating, they may open at 75a, 95a, or even 120a. These are totally unacceptable tolerances in respect to effectively protecting an alternator from excess current while directly charging a battery.

theoldwizard1

SE MI

Senior Member

Joined: 09/07/2010

View Profile


Offline
Posted: 11/08/21 11:00am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Some folks say it is best to add a dc to DC converter to prevent the alternator from overloading.

Concur !

I think the alternator overload is an Internet rumor, but a DC-DC charger, properly configured, will do the best job charging your house batteries.

Teleman

Clayton, CA, USA

Senior Member

Joined: 08/11/2004

View Profile


Offline
Posted: 11/08/21 12:11pm Link  |  Quote  |  Print  |  Notify Moderator

theoldwizard1 wrote:

pianotuna wrote:

Some folks say it is best to add a dc to DC converter to prevent the alternator from overloading.

Concur !

I think the alternator overload is an Internet rumor, but a DC-DC charger, properly configured, will do the best job charging your house batteries.

I just ordered a 40 amp Renogy charger. Now I have to figure out where to mount it and get sufficient 4 ga wire. Stuff ain't cheap...

Gdetrailer

PA

Senior Member

Joined: 01/05/2007

View Profile



Posted: 11/08/21 12:42pm Link  |  Quote  |  Print  |  Notify Moderator

otrfun wrote:

The gist of my comment was to acknowledge a fuses lack of precision. Nothing more, nothing less. *If* a given 60a fuse would precisely open at 61a, then, yes, it could be effectively used for current limiting purposes (i.e., protect an alternator from excess battery charge current). Unfortunately, this is not the case. Given batch of 60a fuses of the same type and rating, they may open at 75a, 95a, or even 120a. These are totally unacceptable tolerances in respect to effectively protecting an alternator from excess current while directly charging a battery.


The "gist" of my comment towards your comments is even IF you were to use a fuse that was say 60A and blew open at 61A that would be a total misapplication if you were depending on a fuse to do this.

That would be pretty dumb to blow and replace a fuse each time you hit say 61A when there ARE devices out there that do that job far better automatically without the need to replace fuses or turn breakers back on.

Fuses and breakers are designed to protect the wiring from becoming the fuse and causing a fire, nothing more and nothing less than that.

Fuses are not "regulators" they are for catastrophic events like a short circuit.

If you want or need current limiting then you need regulator devices which are designed specifically to limit current draw (they do so by reducing the output voltage which limits the max output current).

Switching power supplies like the DC to DC charging units being discussed in this thread typically will have output current and/or voltage limiting already prebaked in.

If you are concerned about how much load the DC to DC power supply charger can draw from your alternator source then select a DC to DC power supply charger with a lower amperage output.

In other words, if 60A is the absolute max you want to draw from the alternator, then select a DC to DC power supply charger that has no more than 40A output capability or even less.

As always, include fuses from your power sources. Select fuse/breaker size to the max allowable amperage of your wire, place it as close to the battery(ies) as possible. Should have a fuse on the vehicle side and a fuse on the lithium battery side and the DC to DC charger goes in between both fuses.

pianotuna

Regina, SK, Canada

Senior Member

Joined: 12/18/2004

View Profile


Offline
Posted: 11/08/21 02:22pm Link  |  Quote  |  Print  |  Notify Moderator

#4 wire is overkill. #8 would be sufficient.

I would put the dc to dc device between the starter battery and the house bank.

That will make for a short run.

Put the dc to DC in a plastic box with no lid to shield it from splashes.

I would add a switched bypass for the dc to dc device.


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

On The Road

Senior Member

Joined: 09/08/2012

View Profile



Good Sam RV Club Member


Posted: 11/08/21 03:36pm Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:

otrfun wrote:

The gist of my comment was to acknowledge a fuses lack of precision. Nothing more, nothing less. *If* a given 60a fuse would precisely open at 61a, then, yes, it could be effectively used for current limiting purposes (i.e., protect an alternator from excess battery charge current). Unfortunately, this is not the case. Given batch of 60a fuses of the same type and rating, they may open at 75a, 95a, or even 120a. These are totally unacceptable tolerances in respect to effectively protecting an alternator from excess current while directly charging a battery.


The "gist" of my comment towards your comments is even IF you were to use a fuse that was say 60A and blew open at 61A that would be a total misapplication if you were depending on a fuse to do this.

That would be pretty dumb to blow and replace a fuse each time you hit say 61A when there ARE devices out there that do that job far better automatically without the need to replace fuses or turn breakers back on.

Fuses and breakers are designed to protect the wiring from becoming the fuse and causing a fire, nothing more and nothing less than that.

Fuses are not "regulators" they are for catastrophic events like a short circuit.

If you want or need current limiting then you need regulator devices which are designed specifically to limit current draw (they do so by reducing the output voltage which limits the max output current).

Switching power supplies like the DC to DC charging units being discussed in this thread typically will have output current and/or voltage limiting already prebaked in.

If you are concerned about how much load the DC to DC power supply charger can draw from your alternator source then select a DC to DC power supply charger with a lower amperage output.

In other words, if 60A is the absolute max you want to draw from the alternator, then select a DC to DC power supply charger that has no more than 40A output capability or even less.

As always, include fuses from your power sources. Select fuse/breaker size to the max allowable amperage of your wire, place it as close to the battery(ies) as possible. Should have a fuse on the vehicle side and a fuse on the lithium battery side and the DC to DC charger goes in between both fuses.
Wow. Did you not see the "*" around the word if? It was a hypothetical to describe the type of precision necessary to safely and effectively protect an alternator while charging a battery directly. No such metallic fuse with such precision exists, so it's clearly a hypothetical.

To be clear: I am NOT, I repeat, NOT, proposing the use of a fuse to limit alternator current to the battery. Why? Because a typical metallic fuse doesn't have the precision or close tolerance to do so safely and effectively.

If you read my previous post I clearly support the use of a dc to dc charger. A 40a dc to dc charger is installed in our truck camper. We run our 11k a/c unit with our 200ah lifepo4 all the time when we're on the road. Need the dc to dc charger to charge our lifepo4 back-up in-time for next break. This dc to dc charger gets one heckuva work out everytime we're on the road during the summer. Works great.

Teleman

Clayton, CA, USA

Senior Member

Joined: 08/11/2004

View Profile


Offline
Posted: 11/08/21 04:07pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

#4 wire is overkill. #8 would be sufficient.

I would put the dc to dc device between the starter battery and the house bank.

That will make for a short run.

Put the dc to DC in a plastic box with no lid to shield it from splashes.

I would add a switched bypass for the dc to dc device.

I was afraid it would overheat in an enclosed box but if not that makes instalation easy. The starter battery and house batteries are very close to each other. Whats the purpose of the switched bypass?

3 tons

NV.

Senior Member

Joined: 03/13/2009

View Profile


Offline
Posted: 11/08/21 06:25pm Link  |  Quote  |  Print  |  Notify Moderator

theoldwizard1 wrote:

pianotuna wrote:

Some folks say it is best to add a dc to DC converter to prevent the alternator from overloading.

Concur !

I think the alternator overload is an Internet rumor, but a DC-DC charger, properly configured, will do the best job charging your house batteries.


Agreed, but since he already has a Victron ‘smart’ shunt, I’d go with a Victron dc-to-dc charger since it too is a Victron format Smart phone capable…

3 tons

otrfun

On The Road

Senior Member

Joined: 09/08/2012

View Profile



Good Sam RV Club Member


Posted: 11/08/21 07:17pm Link  |  Quote  |  Print  |  Notify Moderator

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!

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 6  
Prev  |  Next

Open Roads Forum  >  Tech Issues

 > LiFePo battery upgrade question
Search:   Advanced Search

Search only in Tech Issues


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2022 CWI, Inc. © 2022 Good Sam Enterprises, LLC. All Rights Reserved.