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Old 10-26-2020, 06:45 PM   #1
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12 vs. 24v

Just watched Will Prowse’ comparison of 12 vs. 24v systems (https://youtu.be/Vi7eswWwosk). He had me convinced to go 24v except for a couple of things. He is opposed to charging from the engine alternator. He said there were other options but didn’t say what they are. I think using the alternator guarantees fully charged batteries at the end of a day’s drive. I plan a lithium battery system so will need a DC DC charger if I connect the alternator. Does anyone know what he is thinking for other options than just counting on the solar panels to keep the batteries charged while driving?

He said connecting more than three batteries in parallel leads to problems. if one battery starts to underperform it could lead to reduced battery life. Can anyone enlighten me on this? I originally planned four 105aH Lion Safari UT1300 LiFePo batteries in parallel but now wonder if I should go series and parallel, 2s2p, for 24 volts/210a.

As an aside, the new batteries have 1/4” lugs whereas the cables for the batteries I am removing have 5/16” lug holes. should I replace the lugs Or use them even though they are a little “sloppy”? Also, do all of the cables between the posts, be they series or parallel connected, need to be the same length for all of the baTerries?

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Old 10-26-2020, 07:24 PM   #2
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Go with 4 X 105Ah LiFePO4 batteries in parallel. Stick to 12V for the rest of the system, incluiding the panels. My alternator does a great job of charging my 200Ah of lithium while we're on the road. No added hardware for the dreaded "burned up alternator" warnings. If it happens, I'll deal with it then.
Keep it simple. Don't over think it.
(btw, I think he was talking FLA batteries for the "no more than 3 in parallel" warning)
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Old 10-26-2020, 08:50 PM   #3
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Quote:
Originally Posted by Winterbagoal View Post
Go with 4 X 105Ah LiFePO4 batteries in parallel. Stick to 12V for the rest of the system, incluiding the panels. My alternator does a great job of charging my 200Ah of lithium while we're on the road. No added hardware for the dreaded "burned up alternator" warnings. If it happens, I'll deal with it then.
Keep it simple. Don't overthink it.
(btw, I think he was talking FLA batteries for the "no more than 3 in parallel" warning)
All of these comments are my opinions, and worth exactly what you paid for them.
Good luck with that...I hope it works out for you!!!

It took all of about 25 hours of driving for my 6 Lion UT1300 batteries to take out my 2-year-old 200A alternator.......you're right they charged up very well directly (actually with BIM) from the alternator, just like a Race Car!!! The problem is that race cars get a new engine after every race and the motor in your car is designed to last 100K miles and like your alternator without protection it will blow up just like a race car engine one of these days......most likely when you are out in the middle of nowhere (Murphy's law and all)

To the OP..... a DC-DC converter is a very cheap insurance policy to protect your alternator and thousands of $$ worth of lithium batteries
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Old 10-26-2020, 09:32 PM   #4
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four 105aH Lion Safari UT1300 LiFePo batteries
For that size system, there is little reason to go 24V. That is making some fairly typical assumptions. Four batteries in parallel won't cause you any issues - just be sure your wiring to each of them is adequately sized and exactly the same length.

I use 150A as a rule of thumb when recommending voltages. So as long as your system won't be seeing sustained loads of >1800W, 12V is fine. With that small of a bank, it doesn't sound like you're going to be running >150A loads very often.
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Old 10-26-2020, 10:02 PM   #5
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Good luck with that...I hope it works out for you!!!

It took all of about 25 hours of driving for my 6 Lion UT1300 batteries to take out my 2-year-old 200A alternator.......you're right they charged up very well directly (actually with BIM) from the alternator, just like a Race Car!!! The problem is that race cars get a new engine after every race and the motor in your car is designed to last 100K miles and like your alternator without protection it will blow up just like a race car engine one of these days......most likely when you are out in the middle of nowhere (Murphy's law and all)

To the OP..... a DC-DC converter is a very cheap insurance policy to protect your alternator and thousands of $$ worth of lithium batteries
So 25 hours at 65 mph = around 1625 miles of driving, and your alternator gave out? Hope it was under warranty. Maybe it was faulty from the factory?
My 220A MB factory alternator did 4,000 miles total last February, with one 2 day stop off grid, with no DC > DC after market add ons, and was fine then, and has been fine ever since, and on short 60/120 mile exercise runs, while we wait out the border closure.
Maybe your battery BMS was faulty, or something else caused a massive reserve draw down, that your (possibly) faulty alternator tried unsuccessfully to compensate for?
I hope it works out for you, too.
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Old 10-26-2020, 10:14 PM   #6
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Agree with only 4 batteries, just gets too complicated and expensive to wire everything for 24 volts. Agree with Paul, using your alternator to directly charge your lithiums can cause problems. I put a amprobe on my alternator lead before I got a dc-dc charger and found it trying to push 130 amps to them at idle speed, for a 160 alternator, just too much current with not enough cooling. Besides the dc-dc charger will raise the voltage coming from the alternator to the 14.4- 14.6 volts you need to bring your lithiums to 100% SOC and keep the charging amperage to a reasonably level. As for connections, I used busbars, connecting each battery to it with smaller equal length cables and a larger cable from busbar to loads.
I run a 48 volt system at the house, but have 5200 watts of solar and 21 kw worth of batteries, in this case a higher voltage is justified.
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Old 10-26-2020, 10:23 PM   #7
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Originally Posted by Winterbagoal View Post
So 25 hours at 65 mph = around 1625 miles of driving, and your alternator gave out? Hope it was under warranty. Maybe it was faulty from the factory?
My 220A MB factory alternator did 4,000 miles total last February, with one 2 day stop off grid, with no DC > DC after market add ons, and was fine then, and has been fine ever since, and on short 60/120 mile exercise runs, while we wait out the border closure.
Maybe your battery BMS was faulty, or something else caused a massive reserve draw down, that your (possibly) faulty alternator tried unsuccessfully to compensate for?
I hope it works out for you, too.
You obviously don't read well either

The alternator was 2 years old and it failed that quickly after installing the lithium batteries.

But it's OK you do what you want but.......... encouraging someone else that you have not had issues doing something that is universally known (By experts I mean) to be risky is just silly. It's kind of like saying I've been playing Russian Roulette for a while now and never had an issue......you should try it

Like I said, good luck.............You're gonna need it
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Old 10-26-2020, 10:48 PM   #8
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You obviously don't read well either

The alternator was 2 years old and it failed that quickly after installing the lithium batteries.

But it's OK you do what you want but.......... encouraging someone else that you have not had issues doing something that is universally known (By experts I mean) to be risky is just silly. It's kind of like saying I've been playing Russian Roulette for a while now and never had an issue......you should try it

Like I said, good luck.............You're gonna need it
I read just fine. You lost your 2 year old alternator, coincidentally after installing some Lion Safari lithium jars. It must have been ready to go, because I installed my lithiums on a 2 year old chassis, and everything has been fine. Why does that bother you so much?
Ah, the good old "experts" argument? You know that a lot of those experts have a dog in the fight, selling you stuff you probably don't need.
As for luck, you seem to be the one needing it?
Good luck to you, too.
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Old 10-26-2020, 11:04 PM   #9
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Have followed several AM solar installs [very expensive and quality work] on the Foretravel forum, and on every one, they have used dc-dc chargers, with lithium, or have just not used the alternator to charge the house batteries. With a bigger alternator and only one or two lithium batteries, may not be a problem, but with four 100 a/h lithiums, your max charge rate could be 400 amps if batteries are low. This can strain your alternator and wiring.
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Old 10-26-2020, 11:35 PM   #10
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Have followed several AM solar installs [very expensive and quality work] on the Foretravel forum, and on every one, they have used dc-dc chargers, with lithium, or have just not used the alternator to charge the house batteries. With a bigger alternator and only one or two lithium batteries, may not be a problem, but with four 100 a/h lithiums, your max charge rate could be 400 amps if batteries are low. This can strain your alternator and wiring.
Good point on relationship between total bank capacity, and alternator draw if the bank SoC is very low. In that case, a low capacity/output alternator would be more prone to try to "over achieve" and burn out.
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Old 10-27-2020, 12:11 PM   #11
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As for connections, I used busbars, connecting each battery to it with smaller equal length cables and a larger cable from busbar to loads.
I’ve been curious about busbars for batteries but wonder how they are constructed and mounted. Can you post an image of yours?

I have a slide out tray for my batteries. The cables are 2/0. Magnum says this is good enough for up to 5 feet. If they didn’t need extra length for the slide tray they could come in under that but Holiday Rambler did overkill in my mind and made them about7.5’ in total. I’d like to shorten the cable from the batteries to the On/Off switch but am afraid the pushing and pulling on the first battery post might damage it. Would the busbars negate this concern?
Thanks
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Old 10-27-2020, 12:45 PM   #12
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I’ve been curious about busbars for batteries but wonder how they are constructed and mounted. Can you post an image of yours?

I have a slide out tray for my batteries. The cables are 2/0. Magnum says this is good enough for up to 5 feet. If they didn’t need extra length for the slide tray they could come in under that but Holiday Rambler did overkill in my mind and made them about7.5’ in total. I’d like to shorten the cable from the batteries to the On/Off switch but am afraid the pushing and pulling on the first battery post might damage it. Would the busbars negate this concern?
Thanks
https://www.bluesea.com/products/212..._16in-18_Studs
I use two of these, one for positive and one for negative. equal length leads 4 gauge from each 100 a/h battery to busbars. From busbar to inverter, dc loads etc. 3/0. You can put a switch in this line and leave an extra foot or so, to allow for your slide tray. If you have smaller batteries, you can use smaller wires and busbars, this way no strain on battery connections. Busbars must be firmly mounted in your battery slide with only the big wire off the busbars moving when you move slide in and out.
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Old 10-27-2020, 03:49 PM   #13
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Viewed the link. I like this guy. He makes good points.
105aH Lion Safari UT1300 LiFeP04, website says they are good to go, parallel or series connected. However many of this type are not good for series. Battle Born recommends you specify it so they can ship balanced pairs. It better balances the cell loading and extends life. Some manufacturers battery management system do not allow series.
For 24v systems you need to provide 12v for some items. Electric motors may not be kind to DC-DC power converters. Motors: Slide outs, hitch jack, leveling jacks, furnace blower, or break away trailer brakes.
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Old 10-27-2020, 09:52 PM   #14
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Viewed the link. I like this guy. He makes good points.
105aH Lion Safari UT1300 LiFeP04, website says they are good to go, parallel or series connected. However many of this type are not good for series. Battle Born recommends you specify it so they can ship balanced pairs. It better balances the cell loading and extends life. Some manufacturers battery management system do not allow series.
For 24v systems you need to provide 12v for some items. Electric motors may not be kind to DC-DC power converters. Motors: Slide outs, hitch jack, leveling jacks, furnace blower, or break away trailer brakes.
I have 8 Lion batteries wired in series/parallel in a 24V configuration.

We have 2 sets of DC-DC converters, 1 set (2) of 12-24V converters to manage the charging of the house batteries from the alternator while driving and (2) 24-12V converters to power the house 12V systems including the HWH hydraulic leveling system which draws up to 125A while leveling or extending the slides.

We have had this in place for some time with no issues. We have a matched Victron system with everything running through our CerboGX that allows us to monitor everything remotely in the coach or from anywhere in the world from either smartphone or PC.

We have seen zero issues with any of the 12V systems, they actually run better as the bus gets a constant 13.2V regardless of the state of charge on the battery bank
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