Lithium battery converter size

[D&J]

What amperage converter will I need for two or three 100ah batteries. Same with a DC to DC charger for 12v from the truck.

Denny

[Chad Heiser]

Lithium is happy taking a 0.5C charge rate (where C is the AH capacity of the battery).  Many lithium batteries can do 1C and some can go even higher, but 0.5C is a good rate for longevity of the battery.  With two 100 amp hour batteries, you could easily handle a 100 amp converter.  Make sure the converter is Lithium capable.  It would be the same for the DC to DC charger.  If you are going to have multiple charge sources active at the same time, then the sum of those chargers shouldn’t exceed the 0.5C rate.

Edited October 30, 2023 by Chad Heiser

[oldjohnt]

I agree with Chads good advice and add the following:

   FIRST consult the battery manufacturer regarding their maximum charging amp recommendation, while some like my SOK actually list such right on the battery. If unknown, I likewise would not exceed 0.5C.. As an example, if you used two 50 Amp max charge rate batteries connected in parallel and all was balanced a 100 Amp (suitable for your battery chemistry) would suffice.   

 DC TO DC CHARGER: While the above still applies and any combination/addition of Solar and DC and Charger SHOULD STILL NOT exceed the max charge rate, when selecting the DC to DC USE CAUTION TO NOT EXCEED THE ALTERNATORS RATING. IE just because a 100 Amp charger may be in order DOES NOT necessarily mean a 100 Amp DC to DC should be used IFFFFFFFFF it could over tax the alternator.. Also a diesels alternator is likely higher rated than a gas which may allow use of a bigger DC to DC,  DONT CROWD THE ALTERNATOR WHEN SELECTING A DC TO DC CHARGER and it does NOT necessarily need to be as big as the charger..

 

 John T

 

 

[D&J]

My plans so far is a Renogy 12v 20 amp DC to DC charger, my truck has a 30 amp fused circuit going to the trailer. I just need it to keep batteries up when traveling, we run a residential frig and small freezer. The converter is a Progressive Dynamics 60 amp PF9160ALV with two LiTime 100AH Mini batteries. Does this sound like a good setup.

Denny

 

[oldjohnt]

On 10/30/2023 at 11:06 AM, D&J said:

My plans so far is a Renogy 12v 20 amp DC to DC charger, my truck has a 30 amp fused circuit going to the trailer. I just need it to keep batteries up when traveling, we run a residential frig and small freezer. The converter is a Progressive Dynamics 60 amp PF9160ALV with two LiTime 100AH Mini batteries. Does this sound like a good setup.

Denny

Denny FWIW here’s my response, I’m no expert see what Chad and the others have to say:

1)      A 20 Amp Renogy DC to DC charger (assuming suitable and set for your lithiums) will likely NOT (subject to your alternator) over tax your alternator. You may be able to use a 30 or 40 Amp IF NEEDED, which you may not require (depends on fridge and freezer draw) …

2)      As far as a 20 Amp Renogy DC to DC adequately maintaining your house batteries THAT DEPENDS on 1) The SOC of your house batteries when you start driving 2) The load your fridge freezer and other components draw when driving. The Renogy can deliver 20 Amp Hours of energy for every hour of drive time (20 Amp Hours per Hour of energy) so what is your load and your batteries SOC when starting out ?????

3)      One change I made to my 40 Amp Renogy was NOT to use the auto activation when I started up BUT INSTEAD I installed a manual rocker activation switch BECAUSE I wanted time for my engine to warm up and time to allow my alternator to FIRST charge my engine battery BEFORE drawing alternator current to charge my lithiums. HOWEVER, with an only 20 Amp unit which might draw guessing 24 alternator amps is probably of no concern to allow it to start charging as soon as you start the engine…

4)      A properly sized and protected 30 Amp circuit should suffice for your 20 Amp Renogy as it may draw again guessing 24 Amps INPUT to pump 20 Amps into your lithiums One concern may be line voltage drop on the way back which could necessitate larger wire plus quality 30 Amp or more rated connectors.  

 

John T

Edited November 2, 2023 by oldjohnt

[D&J]

30 minutes ago, oldjohnt said:

Denny FWIW here’s my response, I’m no expert see what Chad and the others have to say:

1)      A 20 Amp Renogy DC to DC charger (assuming suitable and set for your lithiums) will likely NOT (subject to your alternator) over tax your alternator. You may be able to use a 30 or 40 Amp IF NEEDED, which you may not require (depends on fridge and freezer draw) …

2)      As far as a 20 Amp Renogy DC to DC adequately maintaining your house batteries THAT DEPENDS on 1) The SOC of your house batteries when you start driving 2) The load your fridge freezer and other components draw when driving. The Renogy can deliver 20 Amp Hours of energy for every hour of drive time, so what is your load and SOC when starting out ?????

3)      One change I made to my 40 Amp Renogy was NOT to use the auto activation when I started up BUT INSTEAD I installed a manual rocker activation switch BECAUSE I wanted time for my engine to warm up and time to allow my alternator to FIRST charge my engine battery BEFORE drawing alternator current to charge my lithiums. HOWEVER with an only 20 Amp unit which might draw guessing 24 alternator amps is probably of no concern to allow it to start charging when you start the engine…

4)      A properly sized and protected 30 Amp circuit should suffice for your 20 Amp Renogy as it may draw again guessing 24 Amps INPUT to pump 20 Amps into your lithiums One concern may be line voltage drop on the way back which could necessitate larger wire.  

 

John T

My refrigerator draws 56 Watts after it starts up and the freezer just a little more. I've keep my Optima AGM batteries up with the truck for years but my 8 year AGMs are slowly failing and aren't up to the job anymore so I'm looking at changing over to lithium. One of my old Optima batteries will used to start my 5K generator for a starting battery, the old one died and the other will go to my small boat.

Denny

[oldjohnt]

19 hours ago, D&J said:

My refrigerator draws 56 Watts after it starts up and the freezer just a little more.

Even if your fridge and freezer were drawing say 120 total Watts AND THEY DONT RUN CONTINUOUS you know, if your Renogy was supplying 20 Amps at 12 Volts continuous or 240 Watts,  you should be fine, again subject to the lithiums SOC when starting. That 56 Watts seems small ????

John T

Edited October 31, 2023 by oldjohnt

[D&J]

On 10/30/2023 at 12:18 PM, oldjohnt said:

Even if your fridge and freezer were drawing say 120 total Watts AND THEY DONT RUN CONTINUOUS you know, if your Renogy was supplying 20 Amps at 12 Volts continuous or 240 Watts,  you should be fine, again subject to the lithiums SOC when starting. That 56 Watts seems small ????

John T

This is off my inverter with the refrigerator running balanced out, the freezer draws about 10 watts more.

I have everything installed and working and have done a few load tests and it all works great, even better than expected. The only question I have is will it hurt to leave the batteries hooked up after the converter charges them and drops off to 13.6 volts (100% charge) over a long period when we are sitting for the winter in AZ. The way I understand it the converter stops charging when it drops back off to 13.6 volts.

Denny

[Chad Heiser]

Lithium batteries don’t like being kept at a true 100% state of charge for extended periods of time.  Lithium does best when cycled, rather than sitting full.  A good lithium charger will fully charge the batteries and then float them at the top 2 to 3% of the full charge cycle.  What I mean is it will allow the batteries to cycle up and down from 100% to 97 or 98% and then back up again.  This allows the batteries to not stay at a true 100% full charge, but basically remain full for when needed.  If your charger isn’t lithium compatible, then it may or may not keep your lithium batteries full.  Most regular chargers set up for lead acid (or AGM) batteries won’t fully charge a lithium battery up to 100%.  They will get the batteries close, but not all the way.  This could solve your issue.  If your charger does fully charge the lithium batteries, then simply turning the converter breaker off periodically to cycle the batteries while sitting in a full hook up site would also solve your issue.

[D&J]

I did some more digging and my Power Dynamics PD9160ALV converter goes into a charge mode every 3 weeks if batteries are in storage mode like ours are now so I should be good to go. The only thing I have left to do is install a switch so I can turn off to he DC to DC charger if I needed to, this is a 5th wheel so it's not controlled by the trucks ignition switch. On Fords the 12V from the truck is not energized when the truck is off so I ran a wire from the incoming 12V to the ignition port to turn it on when truck is running.

Denny

[kb0zke]

"Lithium batteries don’t like being kept at a true 100% state of charge for extended periods of time.  Lithium does best when cycled, rather than sitting full." We are in the process of installing a substantial solar array on the roof, two 24V 200AH LiFePO4 batteries, and a Victron MultiPlus II. Most of the time we have shore power. I've noticed that the current LiFePO4 batteries (two 12 V 100AH) are always at 100%. I assume that is because the converter is working properly and keeping them charged. Should I do something different?

[lappir]

12 hours ago, kb0zke said:

"Lithium batteries don’t like being kept at a true 100% state of charge for extended periods of time.  Lithium does best when cycled, rather than sitting full." We are in the process of installing a substantial solar array on the roof, two 24V 200AH LiFePO4 batteries, and a Victron MultiPlus II. Most of the time we have shore power. I've noticed that the current LiFePO4 batteries (two 12 V 100AH) are always at 100%. I assume that is because the converter is working properly and keeping them charged. Should I do something different?

That's a very good question and I am wondering too. 

Recently obtained an electric bicycle. In reading the manual it says to leave the battery at less than 100% when sitting for an extended time and only charge it to full just before a ride. That's sure hard to do when you really don't know when you might hop on it. 

My new Motorcycle came with a Lithium starting battery. I'm assuming to diminish weight, but I made the mistake of adding a camera to the bike with a "Parking Monitor" apparently it uses a lot of current and it depleted my brand new bike battery in a couple of days of non riding. I unplugged it when I got a warning that my bike was being tampered with while I could see it and was sure nothing was going on. Caused a computer glitch on the bike requiring a trip to the shop and an $80 hookup charge to reset. 

Thankfully the issue repeated itself before the trip to the shop. I had the battery fully charged and thought I'd plug the camera in for the short ride to the shop, but was stopping at an event for less than an hour. Sure enough I came out to a dead battery again. This time I was close enough to my daughter who has a pocket Jumper device and I was able to ride to my service appointment and arrive on time. 

I don't know what I'll do when it gets below freezing and I want to ride when the roads are dry. I'd rather ride at 20 degrees than 85. I feel like I  can always put on more (or different) layers, but at some point you cannot take off any more and still be safe.  

 

Sort of of off topic, but I wonder how the bike maintains the charge on the battery. I contacted my dealership with a question about putting an AGM in and they suggested not doing so. The charging system is different. 

Rod

[Payroll Person]

15 hours ago, kb0zke said:

"Lithium batteries don’t like being kept at a true 100% state of charge for extended periods of time.  Lithium does best when cycled, rather than sitting full." We are in the process of installing a substantial solar array on the roof, two 24V 200AH LiFePO4 batteries, and a Victron MultiPlus II. Most of the time we have shore power. I've noticed that the current LiFePO4 batteries (two 12 V 100AH) are always at 100%. I assume that is because the converter is working properly and keeping them charged. Should I do something different?

Nope. Compare to the Tesla model 3 manual worth lipo. Charge and use as desired. The small loss from keeping charge and calendar loss is relatively insignificant over the life of the batt.

i have lipo in the rv which keep at 100%. Maybe 5% loss after 24 months. Tesla has 2% loss over a year. Tesla warrants for 8 years or 120k. One can buy a third party warranty to double it.

lipo means we don’t have to be a slave to batt monitoring. 
 

added. My drone batts self discharge to 40/60% after about a week. Designed into the bms. I think they had issues with early batts swelling and have left this “feature” in even though the current batt formula likely does not need it. Of course, many buy and use off brand chargers, so the batt self protecting is not a bad thing. 

Edited December 1, 2023 by Payroll Person

[D&J]

On 10/30/2023 at 10:06 AM, D&J said:

My plans so far is a Renogy 12v 20 amp DC to DC charger, my truck has a 30 amp fused circuit going to the trailer. I just need it to keep batteries up when traveling, we run a residential frig and small freezer. The converter is a Progressive Dynamics 60 amp PF9160ALV with two LiTime 100AH Mini batteries. Does this sound like a good setup.

Denny

 

We made our run from Yuma to Nebraska and the 20 amp DC to DC charger worked perfectly. With the refrigerator, freezer and disk brake actuator running I checked the voltage when we stopped with truck off and it was between 13.6 to 13.8 every time. Because of cold weather we had hookups every night and started with 13.46 volts, that's the normal holding voltage for the converter. I did load tests on the batteries when we were sitting in Yuma so I know they are up to the task but I may still add on more one more. I'm more than happy with the upgrade and would recommend it.

Denny

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[Larry Burkett]

👍👍👍

Larry B