It's finally happened
Submitted: Monday, Jun 30, 2025 at 14:30
ThreadID: 150904
Views:1021
Replies:3
FollowUps:26
qldcamper
After seven and a half years my AGM battery in our camper trailer retired itself from service. It put me at conflict with myself, what do I replace it with? Like everyone I am very curious about lithium batteries but the expense of changing all my charging systems put me off but lithiums are so cheap now, actually cheaper than the AGM brand I have been running.
So I decided to buy a 60ah cheapy from the unmentionable company ( aye Nick ) and have play, after all I've been parallel charging an AGM and a calcium for a few years now quite successfully.
I was correct assuming the Redarc bcdc would think the near flat lithium was fully charged with a terminal voltage above 13 and went straight into float but my AC charger and victron solar reg on the trailer are quite happy to start thumping in as much as they could produce up to 14.4 which I'm happy with.
I have figured out a way to trick the Redarc into charging the lithium and once it's started theoretically should keep charging up to 14.4 also but yet to give it a run for long enough to find out.
All I need to do is unplug the trailer if it goes into float as I will need to do with the solar too but I really don't think it will get that far when I'm away using the battery on solar.
So all happy now I splurged and have bought a 100 AH battery in a different brand because I needed an NS70 case size which limited the market a bit and a 2kw inverter for stand by power for our fridges if we get another week without power because of flooding.
Hooked them up to my induction cooktop to say I'm super impressed would be an understatement, at 93 amps boiled 2 litres of water quicker than I can set up the gas
camp stove. A luxury reserved for sunny days and pack up day knowing it's got a few hours charge time.
Just need to get my oscilloscope off of mothballs to verify the purity of the sine before I plug my fridges into it.
Reply By: RMD - Monday, Jun 30, 2025 at 17:02
Monday, Jun 30, 2025 at 17:02
QLD
Was the cheapy a Lithium or an AGM?
Why would you be running fridges, I presume portable compressor fridges, on an inverter when IF they run on 12v , then simply run them on 12v and not suffer the LOSS through an inverter? Perhaps I missed something there! If you mean 240v House fridges, are they in the camper or house? then a Sine wave inverter will run them. I have been running my house fridge from a 1000w 12v SW inverter for over 2 years, and later switched to a 24v system and a 3000W 24v inverter which runs Vacuum cleaner or Microwave or small bar radiator, with sufficient battery AH. 340AH 24V
Dragging 93 amp out of 100ah Lithium is working it. What is the BMS in the Lithium rated at on DISCHARGE? Most are only around 100 amps , so if you are drawing many amps, the MOSFETS in the BMS will be getting HOT.
Even if you Tricked the redarc , will it drop off charge appropriately so it sits below the STATIC level of the charged lithium and doesn't trickle it?
Startup for a normal fridge is around 800W instant and settles to around 90W. New fridges run less watts. about half the older traditional compressor types.
AnswerID:
648191
Follow Up By: qldcamper - Tuesday, Jul 01, 2025 at 07:06
Tuesday, Jul 01, 2025 at 07:06
Sorry if you were confused, I went back over my post to make it clearer but it seems clear enough. Only people that assume the author is a complete idiot would take it the wrong way.
The first battery I got just to
test my theories is a 60ah and the second a 100ah, the latter rated at 100a continious which understandably works it hard but wouldn't you
test it to make sure it is servicable?
When my 25 amp AC charger hits 14.4 it goes into float but it does start to draw current from the battery slowly rising to 2a for how long I don't know, don't really need to know, just disconnect.
Problem could easily be solved with a simple reverse current relay but why bother? Will the bcdc do the same? Can only assume yes so when my volt meter on the dash tells me it's in float just pull the plug at the next stop. Nothing runs in the trailer while we are travelling.
The inverter which is also an unknown brand just as any other rebranded unit on the market, although coping comfortably at 1300ish watts I'm a bit reluctant to plug 10 grands worth of household fridges into it before I see how clean it's output is.
The inverter and cooktop was not intended to be part of our travelling set up but it is bloody tempting.
FollowupID:
929373
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 01, 2025 at 09:15
Tuesday, Jul 01, 2025 at 09:15
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Hi QC,
Yo say….."When my 25 amp AC charger hits 14.4 it goes into float but it does start to draw current from the battery slowly rising to 2a for how long I don't know, don't really need to know, just disconnect."
That appears to be very odd behaviour for a charger. Are you sure that the charger is actually drawing current from the battery? Could it be that it is actually contributing current to the battery?
The usual behaviour of a charger with float function is to charge up to say 14.4v then go into float mode. At that time the battery terminal voltage is about 14.3 - 14.4 and the charger is producing about 14.2v. As the charger voltage is below the battery voltage there will be no contribution from the charger but as the 'surface charge' voltage of the battery slowly diminishes, a steadily rising small 'float' current may flow from the charger to the battery and settle out at an Amp or two. This description mirrors what you describe as happening to your system.
The charging voltage recommendations for a lithium battery are only little different to those for lead acid and a few people have commented that they have upgraded to lithium but retained their former lead acid charger with complete success, albeit perhaps with a lithium battery not quite fully charged but suitably operational.
Strange that you needed to "trick the Redarc into charging the lithium". Why was that necessary and what did you do?
FollowupID:
929377
Follow Up By: qldcamper - Tuesday, Jul 01, 2025 at 09:50
Tuesday, Jul 01, 2025 at 09:50
Yes weird Allan, at first I thought it was a small positive flow into the battery but then I noticed the -
sign had appeared on the screen. I wouldn't have thought it possible but there it is, maybe a filter cap breaking down in the charger, not overly worried about it.
The bcdc goes straight to float if it sees 13ish plus volts on the load side. It is still charging the flooded battery under the bonnet, so if it is fully charged and I plug in the lithium to the rear of the Ute the almost flat lithium still has the grunt to lift the combined volts past 13 so when the bcdc fires up goes straight to float.
If I let the bcdc start to charge first and plug the lithium in before it goes to float the lithium starts to draw 18 amps and continues charging, theoretically till it hits 14.4, still need to confirm this.
Will be interesting to see if there is any reverse flow when the victron solar regulator goes into float. The two systems are not normally interconnected when charging on solar, both the Ute and trailer have their own solar set ups.
FollowupID:
929378
Follow Up By: Member - LeighW - Tuesday, Jul 01, 2025 at 10:20
Tuesday, Jul 01, 2025 at 10:20
As pointed out very stange, the charger output should drop to around 13.8V and as such its output is less than the terminal voltage of the battery but should not be drawing anything from the battery. Do you have anything else connected to the battery that could be drawing current?
Another other possibility is some AC chargers have fancy rejuvination functions, maybe the charger isn't
happy with the Lithium and is purposely discharging the battery to cycle it?
Also have you actually checked to see there is current flowig out of the battery, maybe the issue is with the battery BMS, it might need to calibrate its self ie battery needs to be fully charged not just taken upto 14.4V though you would think this would present as a capacity issue rather than a current issue.
FollowupID:
929379
Follow Up By: Max E - Tuesday, Jul 01, 2025 at 10:35
Tuesday, Jul 01, 2025 at 10:35
I have 2 different brand drop in lithium batteries with Redarc BCDC. One in ute and one in Van.
Both will always go to 14.4v before dropping to float, from vehicle charge or solar.
Something does not seem right with yours dropping to float instantly.
FollowupID:
929380
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 01, 2025 at 10:42
Tuesday, Jul 01, 2025 at 10:42
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QC, I am confused. You said……. "The bcdc goes straight to float if it sees 13ish plus volts on the load side. It is still charging the flooded battery under the bonnet." Is the bcdc under the bonnet and charging a flooded battery also under the bonnet which then feeds to the rear plug?
FollowupID:
929381
Follow Up By: qldcamper - Tuesday, Jul 01, 2025 at 12:21
Tuesday, Jul 01, 2025 at 12:21
Yes Allan, the rear plug is paralleled to the under bonnet battery.
Leigh, these are all bench tests so to speak so yes have seen the discharge and nothing else connected.
The bcdc is not lithium compatible so thinks 13 volts is a pretty
well charged battery and no the charger is also older so just 2 stage.
FollowupID:
929382
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 01, 2025 at 12:53
Tuesday, Jul 01, 2025 at 12:53
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But where is the bcdc charger positioned? Under the bonnet or in the van?
FollowupID:
929383
Follow Up By: qldcamper - Tuesday, Jul 01, 2025 at 13:12
Tuesday, Jul 01, 2025 at 13:12
Neither Allan, half way between, under the back
seat. Worked pretty
well there since 2013.
FollowupID:
929384
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 01, 2025 at 13:51
Tuesday, Jul 01, 2025 at 13:51
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OK. It was you saying: "It is still charging the flooded battery under the bonnet," that got me confused.
Good luck with it. I believe that lithium is the way to go for most cases although some strong opinions would have it otherwise.
FollowupID:
929385
Follow Up By: qldcamper - Tuesday, Jul 01, 2025 at 14:59
Tuesday, Jul 01, 2025 at 14:59
No worries Allan, as long as it can get a bit of juice back in to these things I'm happy.
I still get 22 amps into the front battery from a 25 amp bcdc when not towing and if I can get 18 into the lithium in the camper while driving I'll be happy.
As long as I can tell when they are fully charged, I'll be able to guestimate when they are getting too low. The fridge runs off the start battery when the engine is running and off the flooded battery while it is not so still know by voltage how that one is going. I imagine if the fridge battery runs low the spare 60ah lithium should dump most of its capacity into it if I couple them up.
FollowupID:
929386
Follow Up By: qldcamper - Tuesday, Jul 01, 2025 at 15:09
Tuesday, Jul 01, 2025 at 15:09
Max, it could
well be doing that but with the lithium connected the voltage m8ght be hitting 14.4 faster than I can get the meter connected. In the past I have noticed when the resting voltage of the flooded battery is 13ish it appears to go straight to float but could be spending half a second or so in absorption first. From memory they switch to float from absorption when the current is 4 or less amps so with a fully charged battery it could all be happening instantly. When the battery is low it climbs slowly to 14.4 at a visible speed.
FollowupID:
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Follow Up By: RMD - Tuesday, Jul 01, 2025 at 19:20
Tuesday, Jul 01, 2025 at 19:20
Qld. I never indicated or said you were and idiot. You brought that up! I am somewhat surprised, after Allan B mentioned you were an Auto Electrician. I presumed you wouldn't have any problems with electrics and a working comprehensive knowledge of it all.
PS. If you drag 1300 Watts out of a 2kw12w inverter for any length of time, it will get quite hot and the fans will be running hard to control internal temp.
In a hotter climate that gets much worse.
This comment is based on what my three
inverters do during the year in Central Vic, with 1 x 1000 w X 12v, 1 X 1000w X 24 v & 1 X 3000w X 24 v.
FollowupID:
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Follow Up By: qldcamper - Tuesday, Jul 01, 2025 at 21:24
Tuesday, Jul 01, 2025 at 21:24
RMD,
Not sure where you come up with the idea I was having trouble working anything out.
As I said to Allan I was simply sharing the results to my tests.
FollowupID:
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Follow Up By: Max E - Wednesday, Jul 02, 2025 at 06:54
Wednesday, Jul 02, 2025 at 06:54
My lithiums rarely get to below 13V as there is not much left after that. I also have a Victron LV Disconnect in the system. They will cut out on low V from the Victron unit rather than their own internal BMS.
If they cut out on the BMS they may need a jump to activate them, with the Victron I just turn them back on and have a bit of time to get them charging.
They are not under constant charge, I turn them on to charge as needed and have a V meter on the dash so can see if anything silly is happening as I drive. One has Victron shunt and monitor, one has built in BT monitoring.
I will be changing the AGM to a Kings 120A lithium in another car, it will be on charge whenever there is solar or car is on.
FollowupID:
929396
Follow Up By: qldcamper - Wednesday, Jul 02, 2025 at 07:19
Wednesday, Jul 02, 2025 at 07:19
Definatly a relearning curve Max.
Voltmeter isn't totally useless, so far I got it down to 13.6 volts while charging means it's somewhere between a bit more to a hell of a lot more time needed, 13.7 it's happening, 13.8 is don't blink or you will miss it.
Amps? Similar to connecting your charging device to a crow bar.
It's similar to when microwave ovens come out and people were blowing their breakfast up all over the country.
FollowupID:
929397
Follow Up By: Max E - Wednesday, Jul 02, 2025 at 07:39
Wednesday, Jul 02, 2025 at 07:39
I have 200Ah batteries, but still not a long time between 14v and a14.4v at 40A charge rate.
Even in Kings batteries there is a difference.
From Ai Google and forums:
"The 100Ah battery uses pouch cells, while the 120Ah battery uses prismatic cells. Prismatic cells offer enhanced durability and protection, while pouch cells are lighter and allow for more flexibility in design."
In my systems I dont run high current loads. If I use an inverter it is only and about 300w max of load. As you would know, running high current loads requires good termination and correct wires sizing etc, otherwise faults and fires are possible. Especially with vibration in mobile applications.
My batteries are rated at100A maximum charge rate and 40A recommended. I dont need to run BCDC units as my alternator is 200A at 14.1 V maximum. But I run BCDCs to limit charge rate, again due to termination etc and also much easier on the batteries.
FollowupID:
929398
Follow Up By: qldcamper - Wednesday, Jul 02, 2025 at 08:01
Wednesday, Jul 02, 2025 at 08:01
Hard to say what is in their batteries, some say pouch but latter ones have prismatic apparently. The 60ah one i got from them, prismatic cells according to the influencers.
The 100ah is not kings but seen a teardown review on it and it seemed as got as any other I've seen, prismatic EVE cells and it was delivered free and was cheaper than the physically larger kings offering. A replacement AGM the same as the one that lasted 7.5 years was almost twice the price.
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