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Open Roads Forum  >  Tech Issues

 > lifepo4 and maxxfan

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mdkelley

Michigan

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Posted: 07/03/21 05:24pm Link  |  Quote  |  Print  |  Notify Moderator

ok. I will check the fuse maybe tomorrow or Monday. Almost done with the AC install and want to knock that out first due to the heat here right now!

otrfun

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Posted: 07/04/21 08:37am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

. . . If it is not too late you might want to return that one for their two-stage version. The original one-stage like you got was a mistake, where they thought an LFP could float on 14.x for an extended time, or else they expected you to not float the LFP at all . . .
Agree.

After doing at least 15-20 heavy discharge cycles with our LifePo4 battery pack using a standard, 3-stage, lead-cell 13.2v/13.6v/14.4v converter, I'm come to the conclusion there's very little to no advantage to using a one or two stage 14.6v dedicated lithium converter (we sold ours). Yes, a 14.6v charge voltage will charge a LifePo4 to 100%. 14.4v will only charge a LifePo4 to ~99% SOC. However . . . lifePo4's don't do well being floated at (or stored with) a high state of charge for long periods of time like a lead-cell battery. IMO there's little to be gained jumping through hoops (purchasing a 14.6v lithium converter) to get that last 1% SOC. If ah capacity is a concern, why not simply discharge 1% lower.

IMO, a single-stage 14.6v lithium converter is far from an ideal choice. It subjects the LifePo4 and all the DC components in the camper to a 14.6v (bulk charge) 24/7/365. IMO a 2-stage or 3-stage converter/charger (of any kind) is a better choice. It will spend the majority of its time in a lower voltage 13.2v/13.6v float/absorption mode---a good thing. Zero chance of overcharging a LifePo4, plus the DC components in your camper won't be forced to operate on the upper end of their voltage range 24/7.

* This post was edited 07/04/21 12:57pm by otrfun *

scbwr

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Posted: 07/05/21 04:27am Link  |  Quote  |  Print  |  Notify Moderator

Re the fan not working: By any chance is there a switch for the fan on the wall? If there is and you simply hooked up all the wires, than the wall switch will still be functioning. I thought of this because I installed a MaxxFan in our bathroom, and didn't bypass the wall switch, so it's easy to try to turn on the fan and have it not work because the wall switch is in the off position.

And yes....I really should take a few minutes and redo the wiring to avoid this problem! It's on the list.......


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mdkelley

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Posted: 07/05/21 07:51am Link  |  Quote  |  Print  |  Notify Moderator

No wall switch, I wired it in directly and also tested it after installing and it worked fine. It just hasn't worked since installing the new high voltage converter and knowing the converter puts out higher voltage I did a web search about voltage and the MaxxFan. What I found was that there were some online who had issues with their fans burning out the circuit board, and MaxxAir told them their fan CB could handle somewhere around 13.6v but any more would fry the CB.

@otrfun - So, it sounds like maybe a voltage regulator would be a good idea between the converter and the camper (not between converter/charger and battery though) due to the higher voltage the single stage PD unit puts out?

I do disconnect the battery when running on shore power/converter because I agree with what you are saying about constantly subjecting the battery to the high voltage bulk charge (since I read on the BB site they say not to leave their battery subjected to the bulk rate for extended periods). I did a lot of reading up on the subject before finally deciding to go with a converter that the battery maker recommended. I am planning to only use this converter to charge the battery when it gets low. I am installing two battery monitors also, one to monitor discharge and one to monitor charge rate and levels. I am honestly brand new to LiFePO4 technology and there is so much conflicting info out there it gets confusing. Thank you all for the help and info.

BFL13

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Posted: 07/05/21 09:28am Link  |  Quote  |  Print  |  Notify Moderator

Try the fan again on battery voltage of 12.x and see if it runs.

It would be silly for the fan to not work at 14.x because on a hot day when you want it, your solar could be at 14.x.

You want a normal converter that does 13.6 most of the time installed in the RV. You could keep the one you have as a portable charger using jumper cable ends for the output to clamp onto a battery. Float the LFP at 13.6 and haul out your portable charger to do the 14.x thing as required.

You can unscrew the bottom of the fan housing ( also the lid crank handle) and see the wiring to the various parts including the CB and wires up to the top of the motor. You can trace the voltage with your meter in different spots to see where there might be a problem.

One I installed had voltage except up to the motor. I happened to tap one of those connections and suddenly the fan started! That is also when I learned about the fan direction rocker switch trick mentioned earlier.


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mdkelley

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Posted: 07/05/21 11:39am Link  |  Quote  |  Print  |  Notify Moderator

From another forum
MaxxFan top voltage = 13.5V per Airxcel, Inc.

Once that fan gets to 13.5 is when its starts to cause concern.

Derek Hicks
Technical Assistance Coordinator
RV Products, a division of Airxcel, Inc.
3050 N. St. Francis
Wichita, Kansas 67219
Office: 316.832.4357
Fax: 316.832.3417
www.Airxcel.com

Gdetrailer

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Posted: 07/05/21 12:42pm Link  |  Quote  |  Print  |  Notify Moderator

mdkelley wrote:

From another forum
MaxxFan top voltage = 13.5V per Airxcel, Inc.

Once that fan gets to 13.5 is when its starts to cause concern.

Derek Hicks
Technical Assistance Coordinator
RV Products, a division of Airxcel, Inc.
3050 N. St. Francis
Wichita, Kansas 67219
Office: 316.832.4357
Fax: 316.832.3417
www.Airxcel.com


Well, for a "device" that is supposed to be designed for a RV that is certainly a stupid voltage rating.

Most devices designed for 12V use like automobiles are typically designed with the capability of dealing with up to 15V DC..

Not all is lost, one can add one or two diodes in series with the fan positive input lead. Each diode will drop about .6V-.7V, two diodes in series should get you about 1.2V-1.4V voltage drop. So, the fan now should be fine with converter voltages up to 14.7V-14.9V.

You will have to chose diodes that have a high enough current rating for the max draw of the fan.

BFL13

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Posted: 07/05/21 12:47pm Link  |  Quote  |  Print  |  Notify Moderator

Would a diode work with the direction choices? I figure the two wires to the fan motor get swapped for pos and neg with the rocker switch so the fan will either suck or blow.

road-runner

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Posted: 07/05/21 02:29pm Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:


You will have to chose diodes that have a high enough current rating for the max draw of the fan.
Have to worry about getting rid of the heat from the diodes, too. Drop 1.5 volts drawing 4 amps and you've got a 6 watt heater. Maybe put the diodes in the air stream the way fan dropping resistors are cooled?


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Gdetrailer

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Posted: 07/05/21 03:00pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

Would a diode work with the direction choices? I figure the two wires to the fan motor get swapped for pos and neg with the rocker switch so the fan will either suck or blow.


Add diode(s) before the direction change switch in that case.

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