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11-23-2020, 09:58 AM
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#1
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Senior Member
Rexhall Owners Group
Join Date: Dec 2010
Location: L.A.
Posts: 412
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DC to DC Charger and lithium
Let me start by saying I'm not a gear head. I'm a 77 year old beginner who hasn't found a mechanic I can trust to work on my Pace Arrow motorhome.
I know the issue has been discussed many times and almost always the suggestion is to use a DC - DC charger to reduce amps to the batteries and eliminate the possibility of damage to the alternator. Most of the threads I've read are about charging the lithium batteries in a travel trailer rather than a motorhome. Also, many of the posts are from owners of trucks that have newer technology smart alternators. So I think I understand their need.
By comparison, my 2005 Pace with it's 8.1 Chevy has an old technology alternator which I believe puts out considerably more amps than either a similar 2005 Chevy truck or a newer truck with a smart alternator. I've also seen the Victron video of an alternator heating up and smoking because it's unable to adequately dissipate the heat build up while at slow speeds. I also read there is a risk of overheating the wire from the alternator to the batteries when using a more powerful alternator.
So with that in mind rather than a DC to DC charger, which increases charge time of lithium why not use an appropriate alternator with a heavier gauge wire?
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GaryB1st
2005 Pace Arrow 35G
2016 Jeep Wrangler JKU Willys trim
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11-23-2020, 10:13 AM
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#2
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Senior Member
Winnebago Owners Club Freightliner Owners Club RV Trip Wizard
Join Date: Nov 2018
Posts: 229
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garyb1st
I'm no expert but, The way I understand it is:
The issue is not so much the charger's ability to produce, but keeping itself from burning up at low rpm. They use an internal fan to keep cool and normally the alternator reduces output while at idle and so the fan is sufficient. But with lithium the draw is not reduced at idle and the fan cannot push enough air to keep it cool.
Hope this helps you understand.
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05 Itasca Meridian 32'
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11-23-2020, 10:16 AM
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#3
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Senior Member
Damon Owners Club
Join Date: Apr 2020
Location: Clovis NM
Posts: 4,389
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You could possibly do that, but you could also go with a Lithium BIM, like THIS.
It would be a lot less expensive than the new alternator, and would guarantee that the alternator wouldn't still burn up.
__________________
2006 Damon Daybreak 3276 35'with 5 Star Tuner. 3 200 Amp Lithium batteries and 2000 watt PSW inverter/charger. 2013 Elantra on a Master Tow dolly.
Retired USAF
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11-23-2020, 10:44 AM
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#4
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Community Moderator
Join Date: Sep 2011
Location: Between the Oceans
Posts: 8,034
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I have observed that our alternator (160a spec) only charged our lithium battery at about 60a-70a under normal driving. The voltage regulator or a built-in module might limit the output to protect the alternator. 5 years with lithium no problem.
__________________
Steven & Polly
2000 Country Coach Intrigue 40' ISC 350
2018 Ford Explorer 4WD
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11-23-2020, 10:51 AM
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#5
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Senior Member
Winnebago Owners Club Freightliner Owners Club RV Trip Wizard
Join Date: Nov 2018
Posts: 229
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Quote:
Originally Posted by CountryFit
I have observed that our alternator (160a spec) only charged our lithium battery at about 60a-70a under normal driving. The voltage regulator or a built-in module might limit the output to protect the alternator. 5 years with lithium no problem.
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CountryFit,
Are your batteries Battle Born brand? As I hear they have a built in regulator.
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05 Itasca Meridian 32'
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11-23-2020, 10:56 AM
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#6
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Senior Member
Join Date: May 2019
Posts: 2,392
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From what I've seen, the problem with going directly from the alternator to the battery bank is trying to keep the voltage at precisely the ideal charging voltage.
Using a DC-to-DC charger puts a true smart charger in control of things and will mean precise voltage levels to the lithium batteries regardless of engine speed or alternator output. You can get DC-to-DC chargers with high output, so this shouldn't be a limiting factor.
__________________
Richard
1994 Excella 25-ft (Gertie)
1999 Suburban LS 2500 w/7.4L V8
1974 GMC 4108a - Custom Coach Land Cruiser
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11-23-2020, 11:08 AM
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#7
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Community Moderator
Join Date: Sep 2011
Location: Between the Oceans
Posts: 8,034
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Quote:
Originally Posted by IMDiesel
CountryFit,
Are your batteries Battle Born brand? As I hear they have a built in regulator.
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No, not Battle Born. I bought CALB lithium cells and built the pack. Couple years later Battle Born was born . My pack has a BMS, so does Battle Born.
__________________
Steven & Polly
2000 Country Coach Intrigue 40' ISC 350
2018 Ford Explorer 4WD
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11-23-2020, 11:19 AM
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#8
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Community Moderator
Join Date: Sep 2011
Location: Between the Oceans
Posts: 8,034
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Quote:
Originally Posted by richard5933
From what I've seen, the problem with going directly from the alternator to the battery bank is trying to keep the voltage at precisely the ideal charging voltage.
Using a DC-to-DC charger puts a true smart charger in control of things and will mean precise voltage levels to the lithium batteries regardless of engine speed or alternator output. You can get DC-to-DC chargers with high output, so this shouldn't be a limiting factor.
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Voltage precision is less concerned actually. Almost all 12v alternators are set at 13.6v output from the factory. Lifepo4 accepts charges without harm up to 14.6v. What importance is to know you have BMS on the lithium battery so to protect the battery in an unlikely event of voltage regulator failure.
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Steven & Polly
2000 Country Coach Intrigue 40' ISC 350
2018 Ford Explorer 4WD
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11-23-2020, 11:23 AM
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#9
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Senior Member
Join Date: Aug 2017
Location: Burien, Wa
Posts: 1,280
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Impressive Steven
Greg
__________________
Greg and Vicki R.
2004 Country Coach Intrigue "Sweet Serenade"
40' Tag Axle Quad slide CCI #11811
16 Jeep Wrangler, Airforce One
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11-23-2020, 12:00 PM
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#10
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Community Moderator
Join Date: Sep 2011
Location: Between the Oceans
Posts: 8,034
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Quote:
Originally Posted by gnvrvin
Impressive Steven
Greg
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I had installed a cut off switch on the alternator leg. But a few times I forgot to turn it off until couple hundred miles later . Then I started to watch the monitor to see how much the current flowing into the battery when DW was driving. There I realized not to worry about it .
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Steven & Polly
2000 Country Coach Intrigue 40' ISC 350
2018 Ford Explorer 4WD
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11-23-2020, 01:07 PM
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#11
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Senior Member
Winnebago Owners Club Workhorse Chassis Owner
Join Date: Nov 2018
Posts: 2,521
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Quote:
Originally Posted by garyb1st
rather than a DC to DC charger, which increases charge time of lithium why not use an appropriate alternator with a heavier gauge wire?
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Have you priced a high output alternator, shoehorning it into the engine bay and rewiring your DC supply (cables, isolation relay, et al) to handle that elevated current?
Mark B.
Albuquerque, NM
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11-23-2020, 01:38 PM
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#12
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Senior Member
Rexhall Owners Group
Join Date: Dec 2010
Location: L.A.
Posts: 412
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Quote:
Originally Posted by CountryFit
I have observed that our alternator (160a spec) only charged our lithium battery at about 60a-70a under normal driving. The voltage regulator or a built-in module might limit the output to protect the alternator. 5 years with lithium no problem.
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This is encouraging. I don't know how to determine the amps that are being put out by the alternator. How do you do it?
We have 2 Lion Energy 1300's 100 Ah batteries that have built in BMS so hopefully that will protect the batteries if we exceed the 14.6 - 8 maximum.
Did you do anything to the wire from your alternator to the house batteries? I know a Country Coach has more house batteries than our Pace so yours may already have a heavier gauge wire.
__________________
GaryB1st
2005 Pace Arrow 35G
2016 Jeep Wrangler JKU Willys trim
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11-23-2020, 01:49 PM
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#13
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Senior Member
Rexhall Owners Group
Join Date: Dec 2010
Location: L.A.
Posts: 412
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Quote:
Originally Posted by HarryStone
You could possibly do that, but you could also go with a Lithium BIM, like THIS.
It would be a lot less expensive than the new alternator, and would guarantee that the alternator wouldn't still burn up.
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Wiring the dc to dc charger looks pretty straight forward. But it requires a wire to an ignition source to turn it on. I can probably do the positive and negative leads but wiring to an ignition source is something I'm not sure I want to do. Does a BIM also require a wire to an ignition source?
__________________
GaryB1st
2005 Pace Arrow 35G
2016 Jeep Wrangler JKU Willys trim
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11-23-2020, 01:55 PM
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#14
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Senior Member
Join Date: Jul 2018
Posts: 2,812
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I have a victron 712 on my battleborn lithium batteries, when connected directly to alternator have seen 130 amps from alternator to batteries from a 160 amp alternator, too much current for me especially at idle speeds, Depending on type of lithium battery and their BMS's, some will accept a high charging rate and some will not. Battleborn's will accept a 1C charging rate which is 100 amps. I installed a dc-dc charger which not only limits the current, but will boost the 13.2 nominal voltage [when start battery is fully charged] to the 14+ volts necessary to bring them to 100% SOC.
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Foretravel tag axle 40 ft. 500 hp/1550 ft/lbs ism 1455 watts on the roof. 600 a/h's lithium down below.
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