Lithium battery in Lil Snoozy - Page 3 - Fiberglass RV


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Old 06-25-2018, 08:19 AM   #29
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Originally Posted by Banjo Bob View Post
Thanks to all who contributed to this thread. I've sold my tent trailer and I'm awaiting the Snoozy. I've never hooked up to power so I'm interested in being able to remote camp for 4 - 5 days and taking some power with me. My house is solar powered so I have some basic knowledge. I've got a lot of reading to do.
We just got back from a week-long trip with the Snoozy. Longest stretch without power was 45 hours. We used the fan for about 15 minutes and the water pump only for flushing. Lights were used at night but generally only to prepare for bed. The fridge was the main load. Temperatures were 90's day and 60's night. Total power used was 59.5 Ah. The average draw was about 1.3 amps/hour.

On the five hour drive home, with the fridge still on, the truck recharged the battery 30 Ah.
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Old 06-27-2018, 09:52 PM   #30
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Doug,
I want to thank you for the information in this thread. It has completely changed my battery plan for my camper. I am planning to construct my own bank out of 4 individual LiFePO4 cells. And a separate battery management system.

I have a question about your DC to DC converter. Have you measured the voltage at the input of the Converter? Or the voltage at your vehicles battery when the alternator is changing. I am curious about the voltage drop in your setup.
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Old 06-29-2018, 10:40 AM   #31
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Replace the stock 12 gauge charger/converter wiring with 6 gauge so you can charge at up to 60 amps.
You'd think they would wire it properly. Thanks for this tip. I'll have to do that with my converter for sure

I have also installed a Li battery in my trailer and am going to charge via TV battery with the TBCM-40A.

I am also very pleased that you can put this battery on its side.

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Old 06-29-2018, 06:23 PM   #32
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Originally Posted by buff30 View Post
I have a question about your DC to DC converter. Have you measured the voltage at the input of the Converter? Or the voltage at your vehicles battery when the alternator is changing. I am curious about the voltage drop in your setup.
I measured voltage at the battery then went to measure input and output at the DC/DC converter. The battery was easy but the converter would have required me to uninstall the wires and put in jumpers, which was more work than I wanted to do. But when charging on the road with a partially discharged battery, the 9 amp rated converter charged at 8.5 amps, so I figured voltage drop was not an issue with my setup. Remember that I doubled the 12 gauge wire in the trailer, from 7-pin connector to the converter. I hope this helps.
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Old 06-29-2018, 06:27 PM   #33
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Originally Posted by fofobraselio View Post
You'd think they would wire it properly. Thanks for this tip. I'll have to do that with my converter for sure

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Well, the Snoozy wiring was for a lower amperage rated charger/converter, so it didn't need the 6 gauge wiring for the 60 amp charger I installed. But I agree, Snoozy undersized the wiring - 12 gauge is too small for the WFCO 35 amp charger that came with it.
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Old 06-29-2018, 06:28 PM   #34
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No worries thanks for the help.
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Old 06-29-2018, 08:56 PM   #35
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3 feet of 12 gauge at 60 amps would have a 0.3 volt drop. Note the charger is only outputting its max current when the battery is heavily discharged, as the battery charge voltage rises, the current drops so that voltage drop reduces proportionally... 6 gauge is probably total overkill, I bet 10 ga would have been sufficient here, unless you've got a long run form the charger to your battery.
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Old 06-30-2018, 02:15 AM   #36
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Originally Posted by John in Santa Cruz View Post
3 feet of 12 gauge at 60 amps would have a 0.3 volt drop. Note the charger is only outputting its max current when the battery is heavily discharged, as the battery charge voltage rises, the current drops so that voltage drop reduces proportionally... 6 gauge is probably total overkill, I bet 10 ga would have been sufficient here, unless you've got a long run form the charger to your battery.
John,

I do have a long run from the charger to the battery; Lil Snoozy puts it on the other side of the RV, so it runs about 7 feet. The Blue Sea Systems ampacity chart I used says to use 6 gauge for a run of 7 to 10 feet, for 60 amps, with a 3% voltage drop. It actually says to use 6 gauge for 0 to 6 feet also. Here is the link to the site I used:
https://www.bluesea.com/support/arti...r_a_DC_Circuit

So maybe they are too conservative but when my battery is pretty depleted, the charger is putting out 59+ amps and the 6 gauge wire is warm. It continues to put out over 50 amps for much of the charge cycle because the charge curve of the Li battery is so flat until it is almost charged.

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Old 06-30-2018, 02:36 AM   #37
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ah, cool. yeah, 7 foot run, and its actually running 60 amps most of the charge? I retract whatever I said...

hey, is the lithium charge controller monitoring the temperature of the lipo? those things get WARM when they are being charged, and if the temp gets too high, the charger really should back off, or they can go BOOM.
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Old 06-30-2018, 05:45 AM   #38
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hey, is the lithium charge controller monitoring the temperature of the lipo? those things get WARM when they are being charged, and if the temp gets too high, the charger really should back off, or they can go BOOM.
Battle Born says each individual cell is monitored for charge and high and low temperature. The BMS is built in to the battery. I think that is the "drop-in replacement" part of their claim -- I don't need a separate battery monitoring system, including temperature.

Also, to clarify, 59.5 amps is the highest I have seen and it doesn't charge at that the whole time, it does drop off. But is stays in the 50s for a long time. I really love that about the battery because it is totally charged in a couple of hours.
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Old 06-30-2018, 12:57 PM   #39
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I discovered another solution to the problem of charging lithium from an alternator.

https://battlebornbatteries.com/ster...ttery-charger/

Sterling Power offers several models depending upon system needs. It is a step up DC to DC constant current battery charger. I believe it it can also act as a battery isolator separating the tow vehicle charge system from the campers system. I am still trying to figure out if it accomplishes this through solid state or a standard relay.

I think this model would fit the bill for most of us however they have lower and higher amp rated models.

Sterling Power battery to battery charging system - battery to battery charger, marine grade DC powered charger
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Old 06-30-2018, 02:30 PM   #40
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Doug,

For what is worth from my training and years of experience as an aviation electrician I believe you have designed an effective system. Like others have voiced I would definitely change out your main 300 amp fuse and this is why. Starting with the BB 100ah battery, it's max Continuous discharge current is rated as 1C or 100 amps. It has a 2C, 200 Amp Surge Current (30 Seconds) and 1/2 second surge for higher loads. That being said you should never be drawing much over 100 amps from the battery. So a 1000 watt inverter is the max you could run off this battery, depending on efficiency and load it would draw about 100 amps DC at full load. The BB-100's internal BMS is designed to disconnect the internal battery cells from the external battery posts if the load is between 101 to 200 amps for more than 30 seconds and 201 or greater amps for .5 seconds. That all being said the safest thing for the battery is to never subject it to the overload conditions. As long as the electronic BMS does not fail or malfunction it should provide a level of safety from an overload or direct short to ground. I personally know that even the best design and manufacturer electronic circuitry is subject to failure. In the aircraft industry and I am sure other industries they design levels of redundancy to mitigate the risk of failure of critical systems. In this case a properly sized fuse can act as a level of redundancy for this function of the BMS. A 125 to 130 amp fuse connected directly to the positive terminal of the battery would allow you to use a little of your overload capacity before opening keeping your expensive battery far away from its damaging over load range of 200 amps.

As far as protecting the wires between the battery and the loads-charging sources I can only speculate as I have not seen a schematic of your system. From studying the posts I will explain how I pictured myself setting up your system. This advice is only valid if your system is wired exactly as I describe. If you have a sketch I would be happy to take a look.

From the 125 amp fuse mounted directly on the positive post I would run 6awg duplex cable, positive wire to the 60 amp charger and negative wire directly from your negative bus near the battery to the charger. The 125 amp fuse is at the max for this wire size but is in the safe range. Also from the 125 amp fuse you need to connect your DC loads. You said your loads were protected by a 30 amp circuit breaker. This needs to be placed as close to the main 125 amp fuse as possible as any length of wire between the main fuse and the 30 amp breaker will not be protected unless it is also 6awg or larger. If your new battery is not in it's original location you would need to ensure the wire supplying the panel is still sufficient. I am not sure where your DC-DC converter is connected to the system but if it's mounted right next to the battery with a short direct run or wire, a separate fuse between it and the battery may not be required. If that is the only connections to the positive side of the battery I think you would be good. Where is your main disconnect switch located? Negative or positive side?

I will write a separate post about your charge rate.

This is only constructive criticism and not intended to be an internet arm chair expert one upper. Like I said before I appreciate the contributions that this thread has brought to our little community.
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Old 06-30-2018, 07:26 PM   #41
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As far as the ideal charge current I cannot find a single spot on Battle Born's web site where they specify the recommend charge rate or max charge rate. I am pretty certain BB doesn't manufacture the cells they place inside their batteries as I am not aware of a source outside of China for LIFEPO4 cells. Cell manufacturers normally publish this data on a spec sheet. I know they use cylindrical cells from a YouTube video were I could see their batteries being assembled in the background. So I will use the common 10ah 3.2 V cell for discussion. And industry standards for LIFePO4 in general.

http://www.batteryspace.com/lifepo4-...-3-passed.aspx

This cell recommendeds a charge rate of 2C, and a max of .5C however it does alow a rapid charge of 1C.

IEC standard for LiFePO4 state the cell should last for > 2000 cycles and retain 80% of initial capacity of the cell when changing at a 0.2C rate.

Most manufacturers list their charge rate at .25C to .5C. Following theses guidelines would give us a 25 to 50 amp charge rate on a 100ah battery. Staying within these parameters would likely result in the best longevity. However depending on the individual requirements of a particular system, a shorter charge time my be more important than long battery life. If I was designing a 100ah LiFePO4 I would go with a 30 to 40 amp charge rate.

This doesn't mean a .6C rate is unsafe if the manufacturer doesn't forbid it as most LiFePO4 allow up to 1C charge rate.
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Old 06-30-2018, 08:06 PM   #42
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the chinese are *terrible* on specs and documentation for electronics and software.
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