Fitting high capacity AGM's

boybach

boybach

Well-known member
Dec 9, 2020
1,033
194
63
Hi all, I'm in line to get a pair of used (but well within service life) Lifeline 300AH AGM batteries. They are big marine deep-cycle units weighing
90lbs apiece and physically able to fit in the battery compartment (if I can manage to pick them up, that is :) )

These batteries

https://lifelinebatteries.com/products/marine-batteries/gpl-6ct/https://lifelinebatteries.com/products/marine-batteries/gpl-6ct/

John Lebetski, Bruce Hislop, Billy Massey and I have discussed the implications of installing these beasts, i.e. the effect on the alternator if used
as a "drop-in" replacement without any modifications.

I have to admit that I don't understand the science or math behind the problem, but I do get the point that the alternator would be overworked
constantly trying to bring the battery bank up from a state of low charge, resulting in a cooked alternator. We don't want that.

Charging from the Onan/shore power via the converter would be ok as my converter has an AGP accessory port.

The solution suggested by Bruce was to install a DC-DC charger and wire it in parallel with the converter. I get that. I plan to get either the 40amp
or maybe the 20amp Renogy unit as they seems fairly affordable compared to the others I saw out there.

https://www.amazon.ca/s?k=Renogy+40A+DC+to+DC&i=automotive&ref=nb_sb_nosshttps://www.amazon.ca/s?k=Renogy+40A+DC+to+DC&i=automotive&ref=nb_sb_noss

Even though hooking up the charger "in paralell" to the converter may seem like a fundamental job to an electrician, I'm afraid I find it a mite
intimidating, both as far as the physical location and hookup goes. At first I thought I could locate it in the electrical compartment next to the
converter but because these Renogy units don't have auto switching and require an "ignition on" connection to switch on, I started thinking maybe the
best place would be up front on the firewall?

If that location on the firewall is a possibility, could I also connect the main terminals of the charger there?

Do I need to fit a Yandina combiner too?

As the batteries (chassis lead-acid)are different types, will the AGP's drain the chassis battery or vise-versa? OTOH, am I overthinking this whole
thing? :?

TIA for any input,

Larry

--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
Lots of good info on this site re batteries and charging. Its a boating site, but applies to RV's as well

Read here:
https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

and here
https://marinehowto.com/alternators-voltage-sensing/

and the links here
https://marinehowto.com/category/electrical/batteries/
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
> Lots of good info on this site re batteries and charging. Its a boating site, but applies to RV's as well
>
> Read here:
> https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/
>
> and here
> https://marinehowto.com/alternators-voltage-sensing/
>
> and the links here
> https://marinehowto.com/category/electrical/batteries/

Well great info but sure a lot to digest for what I initially imagined would be a simple battery swap.

As I don't seem to be any further ahead on placement of the DC-DC charger and the relationship between the Onan/converter/alternator/isolator and how
that relates to the existing system, I'm thinking I might just abandon this opportunity of acquiring these AGM batteries (for a song btw) and head
over to the local Costco for a couple of 6v golf cart units. I'm not even sure whether the AGM batteries would be fully chargeable even if I added the
DC-DC charger.

oh well.

Larry
--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
Hi Larry,

Sorry I'm not able to give you specific details on how exactly to do this. I'm an electronics guy with over 40 years experience in mobile electronic
systems, specifically mobile radio communications (think police, fire and taxi radios). I did a lot of battery backup systems for public safety radio
systems so I have experience with deep cycle batteries arrays and charging systems. But I'm not an Engineer so I'm not in the position to design
something for you.

The links above give great info on charging various battery chemistries in the mobile environment. I find it better to understand the various systems
in our motorhomes, than to blindly hook them up and trust their operation will be trouble free. We take these things hundreds or thousands of miles
from home. If there is a problem the chances of finding a RV dealer who's Technician can troubleshoot anything is very remote.

I believe the Victron website has some hookup diagrams that might help.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Thanks Bruce, appreciate your help and guidance.

If I could see a hookup for adding a DC-DC charger to a system like my own, chassis battery up front connected to an isolator that via the alternator
charges both chassis and house bank - and - a converter/shore connection that only charges the house bank then I'd be set.

I can't imagine I'd be the first guy adding AGP batteries to a TZE, but you never know.

All the best

Larry
--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
Larry,
The DC-DC charger eliminates the isolator since it also will isolate the chassis battery from the house battery when the charger is OFF. Remove the
wire from the isolator to the house battery side of the Boost solenoid. Move the alternator wire from the center terminal of the isolator to the
chassis battery side of the isolator and leave the isolator in place for now. The alternator will now directly charge the chassis battery.

I ran a wire from the large "Chassis Battery Positive" terminal which is near the isolator under the passenger side hood. For my 20Amp unit I ran #8
wire to the rear house electric cabinet where I installed the charger. You will want a larger cable for higher current models. Remember a 60 amp
Renogy unit will consume more that 60 Amps on the input side due to losses in the charger and also the fact it will likely be outputting a higher
voltage than input.

Example:
Output 60A at 14V = 840W
Input: Chassis voltage = say 13.8V less losses in 30ft of wire and return on ground (say 1.5V) = 12.3V
840W/12.3V = 69Amps plus conversion losses (10-15% so say 15%) = 80Amps

So in this case the alternator needs to deliver 80Amps. So you will need to up the alternator capacity to about 150Amps to also supply power to the
chassis and to have some overhead capacity so you are not running the alternator near maximum rating. Or reduce the size of the charger to 40Amps, but
it will take longer to charge. The Renogy chargers have a Low-Power mode which reduces the charge current by 50% (30Amps for a 60 amp unit). So you
could enable that until you installed a larger charger.

The output of DC-DC charger is simply connected to the house battery. The output of the converter/charger is also connected to the house battery.
The Renogy chargers require an ignition source to enable the charger.

Here is a link that may help.
https://weekendervanlife.com/install-a-dc-dc-battery-charger/

But you didn't hear any of this from me!

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Appreciate you going the extra mile for me Bruce.

Thanks again, I'll probably go for a 40 or even a 20 amp charger but I'll check out the link you didn't :roll: send first

Larry
--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
Just another thought for you. Lots of people (including me) have been putting a pair golf batteries in GMCs for years using the the original 80 amp
or upgraded 100 amp alternators with no problems. I believe the golf cart batteries are rated around 215 for a 20 hour draw, while your proposed ones
are rated around 300. Since both types of batteries should not be discharged more than 50 % the amount of charging current they will draw will
probably be withing manageable rates as is.

There are other variables you have not considered including the voltage drop of 20+ feet of cable and the fact that most alternators will not put out
their rated current when they get warmed up.

Most batteries will not take a much of charge until they warmed up and the reverse EMF gets higher as they start charging charging rate.

Some alternators also reduce the charging voltage as they warm up.

What about single belt alternator pulley slippage. Will it be a problem?

The GMC as deigned has a 50 amp CB in line to the rear so you should never be able to draw more than that going to your house batteries.

There are just too many variables to guess at and engineer around. I am suggesting that you hold up on the modifications and see if you really have a
problem before you try applying a solution to fix it.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
My comments to Larry were essentially the same as Ken's. My combined
battery capacity is similar to two 6V GC batteries (except dual 12V's
connected via an A/B switch - single battery when discharging, dual
batteries when charging) and AFAIK AGM batteries are similar chemistry
as flooded lead acid. I'm thinking about replacing my upfront coach
battery with dual 6V GC batteries when it's time for replacement.

I've never had issues (other than one alternator years ago), even though
we usually dry camp - often for up to 5-7 days at a time.

But I definitely lean towards KISS principles, especially for my camping
vehicle.

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

> Just another thought for you. Lots of people (including me) have been putting a pair golf batteries in GMCs for years using the the original 80 amp
> or upgraded 100 amp alternators with no problems. I believe the golf cart batteries are rated around 215 for a 20 hour draw, while your proposed ones
> are rated around 300. Since both types of batteries should not be discharged more than 50 % the amount of charging current they will draw will
> probably be withing manageable rates as is.
>
> There are other variables you have not considered including the voltage drop of 20+ feet of cable and the fact that most alternators will not put out
> their rated current when they get warmed up.
>
> Most batteries will not take a much of charge until they warmed up and the reverse EMF gets higher as they start charging charging rate.
>
> Some alternators also reduce the charging voltage as they warm up.
>
> What about single belt alternator pulley slippage. Will it be a problem?
>
> The GMC as deigned has a 50 amp CB in line to the rear so you should never be able to draw more than that going to your house batteries.
>
> There are just too many variables to guess at and engineer around. I am suggesting that you hold up on the modifications and see if you really have a
> problem before you try applying a solution to fix it.
 
Larry,

AGM batteries are not totally different battery chemistry, like lithium ion - I think of them as basically spill-proof and maintenance-free lead acid
batteries. My Birchaven came with two Optima Red Top house batteries that were 5 years old, and I continued using them without issue for another 6
years. I have an isolator and a Blue Sea Combiner with a Progressive Dynamics PD9260.

You might want to change your existing converter/charger setup with the big AGMs because of the battery charging time if they are pretty deeply
depleted, but without knowing your boondocking and battery use, it isn't necessarily mandatory.

Richard
--
'77 Birchaven TZE...777;
'76 Palm Beach under construction;
‘76 Edgemonte waiting its turn
 
Appreciate all the tips guys, maybe I will be ok just sticking them in there and adding the AGM module to my IOTA55 amp converter.

This is my typical usage situation. I have no shore power where I store the coach so charging at home base in a no go. I very rarely camp with hookups
at the moment, almost always boondocking within 100 miles of home base. I use the house batteries for interior lighting (all led's), water pump,
fridge, charging flashlight/phones/computer and early/late season furnace. That's it.

Back in March, when I knew nothing about TZE's or motorhomes in general, I bought the coach with a dead 12v house battery. My first instinct was to
get a new battery in there so I could get the systems up and running.
Because I didn't know any better, I couldn't see the point of buying 2 6v units so I bought the largest single 12v deep-cycle battery that would fit.
Keep in mind that I didn't really have a clue what AMP hours meant in practical terms back then.

Fast forward to the summer when I started seriously using the coach. I'd switch on the fridge for a day before taking off and even though it was on
propane, overnight the eyebrow control board and fan took enough amps to knock the battery down to the 11v range. After a run of course it came back
up but it's been a constant PIA especially when I've left the porch light on and things like that. The biggest draw of course was late in the season
when I started running the furnace. Those 8 amps took the battery down to the 9v's and sometimes 8v's, so I'd have to start the Onan using the boost
switch.

Basically I don't have enough reserve power with that 120AH 12v battery.

When I was offered the 300AH AGP batteries, I thought I'd be in fine shape next season - perhaps I will!
I just don't want to kill the AGP's by over or undercharging. From what I've gleaned over the last little while, AGP's are very sensitive in that
dept. and continuous over or under charge will permanently damage them.

Larry


--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
I find it interesting that your IOTA has an AGM module and when I look at the specs for my Progressive Dynamics unit - they mention that they fully support proper charging of AGM batteries, out of the box. That tends to follow what I know about them - they are very close to plug-in replacements for flooded lead acid batteries.

My use case is very similar to yours - but when I’m on my first 120 AH battery (true deep cycle - lots of deep cycle batteries are actually hybrid marine starting/deep-cycle batteries) will last for days (probably 5 days, less with furnace usage). My second battery is smaller - 100AH (a #24) and usually when I have to change over, I use that as my trigger to charge (either Onan or engine, depending on the plans).

I get a GOOD charge from relatively short runs (usually 100-200km?) between campgrounds. My 70A PD convertor charges pretty quickly as well - but I’ve never really quantified it.

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

>
> Appreciate all the tips guys, maybe I will be ok just sticking them in there and adding the AGM module to my IOTA55 amp converter.
>
> This is my typical usage situation. I have no shore power where I store the coach so charging at home base in a no go. I very rarely camp with hookups
> at the moment, almost always boondocking within 100 miles of home base. I use the house batteries for interior lighting (all led's), water pump,
> fridge, charging flashlight/phones/computer and early/late season furnace. That's it.
>
> Back in March, when I knew nothing about TZE's or motorhomes in general, I bought the coach with a dead 12v house battery. My first instinct was to
> get a new battery in there so I could get the systems up and running.
> Because I didn't know any better, I couldn't see the point of buying 2 6v units so I bought the largest single 12v deep-cycle battery that would fit.
> Keep in mind that I didn't really have a clue what AMP hours meant in practical terms back then.
>
> Fast forward to the summer when I started seriously using the coach. I'd switch on the fridge for a day before taking off and even though it was on
> propane, overnight the eyebrow control board and fan took enough amps to knock the battery down to the 11v range. After a run of course it came back
> up but it's been a constant PIA especially when I've left the porch light on and things like that. The biggest draw of course was late in the season
> when I started running the furnace. Those 8 amps took the battery down to the 9v's and sometimes 8v's, so I'd have to start the Onan using the boost
> switch.
>
> Basically I don't have enough reserve power with that 120AH 12v battery.
>
> When I was offered the 300AH AGP batteries, I thought I'd be in fine shape next season - perhaps I will!
> I just don't want to kill the AGP's by over or undercharging. From what I've gleaned over the last little while, AGP's are very sensitive in that
> dept. and continuous over or under charge will permanently damage them.
>
> Larry
>
>
> --
> Larry - Victoria BC -
>
> 1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
> exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
 
> I find it interesting that your IOTA has an AGM module and when I look at the specs for my Progressive Dynamics unit - they mention that they
> fully support proper charging of AGM batteries, out of the box. That tends to follow what I know about them - they are very close to plug-in
> replacements for flooded lead acid batteries.
>
> My use case is very similar to yours - but when I’m on my first 120 AH battery (true deep cycle - lots of deep cycle batteries are actually
> hybrid marine starting/deep-cycle batteries) will last for days (probably 5 days, less with furnace usage). My second battery is smaller - 100AH (a
> #24) and usually when I have to change over, I use that as my trigger to charge (either Onan or engine, depending on the plans).
>
> I get a GOOD charge from relatively short runs (usually 100-200km?) between campgrounds. My 70A PD convertor charges pretty quickly as well - but
> I’ve never really quantified it.
>
> Rob
> Victoria, BC
> 76 Royale - Rear Twins/Dry Bath

Rob - my IOTA has various plug-in gizmos (gizmii?) to suit whatever chemistry you are running, even LiFePo4.

https://www.iotaengineering.com/products/detail/1195175/iota/iq4-agm-smart-charge-controller/3-stage-smart-charge-controller-for-the-iota-dls-tailored-absorption-charging-for-agm-batteries

Larry

--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
Yes - I saw that when reading about your converter. But Progressive Dynamics indicates their converter works with AGM out of the box:

https://www.progressivedyn.com/service/frequently-asked-questions/

Lithium batteries are VERY different chemistry and have very different charging requirements.

Rob
76 Royale Twin Beds, Dry Bath
Victoria, BC

>
> Rob - my IOTA has various plug-in gizmos (gizmii?) to suit whatever chemistry you are running, even LiFePo4.
>
> https://www.iotaengineering.com/products/detail/1195175/iota/iq4-agm-smart-charge-controller/3-stage-smart-charge-controller-for-the-iota-dls-tailored-absorption-charging-for-agm-batteries
>
> Larry
>
>
> --
> Larry - Victoria BC -
>
> 1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
> exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
Anyway Rob, it ain't the converter side of things I'm concerned about, it's the alternator side.

Larry
--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
> Anyway Rob, it ain't the converter side of things I'm concerned about, it's the alternator side.
>
> Larry

OK Larry,

Now that we have the whole story...

Let's start with the fact that you 120AH battery was undersize (all of us with experience know this all to well). What you also may not know is that
your current house battery is probably not 120 today. It only takes a couple of runs below 10V to hurt it. Depending on who you read, a 50%
discharge is 11.8~12.0V and below that for much time at all is damaging. That be as it may, you now have a good set to cram in there.

Given you specific situation, there are two things to not worry about. Use the OE charging system as it was built. It will be just fine. I do not
know if you have the 80 or 100 amp 27SI in there, but that is little matter. Those machines are well enough protected on their own. If it still has
a single belt, you can't hurt it. Even with the double belt, that #4 wire and the 50 amp breaker will effectively protect your charging system. It
may take a lot of driving time to recover the house bank.

That Iota converter is just what you need, leave it alone. But, you knew that.

As you store the coach without shore power, I suggest that you get some solar onboard. You can start with a 5~10 watt panel in a sunny window just to
keep the house bank at full density.

I think you are in good shape on your current track. Most of all, you are enjoying the coach. That is what so many miss getting to.

Matt Colie
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
Go with Matt's advice.
You will not regret the choice.

What are you paying for the batteries?
--
1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
 
> Go with Matt's advice.
> You will not regret the choice.
>
> What are you paying for the batteries?

One hundred and twenty five C$ apiece tax incl.

Larry

--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
> It may take a lot of driving time to recover the house bank.
>
> That Iota converter is just what you need, leave it alone. But, you knew that.
>
> As you store the coach without shore power, I suggest that you get some solar onboard. You can start with a 5~10 watt panel in a sunny window
> just to keep the house bank at full density.
>
> I think you are in good shape on your current track. Most of all, you are enjoying the coach. That is what so many miss getting to.
>
> Matt Colie

Thanks for the vote of confidence Matt. Regarding this solar panel in the window, how to I hook it up to charge the house bank?

Larry

--
Larry - Victoria BC -

1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS
exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
 
> Thanks for the vote of confidence Matt. Regarding this solar panel in the window, how to I hook it up to charge the house bank?
>
> One hundred and twenty five C$ apiece tax incl.
>
> Larry

Larry,

You said you have a Palm Beach, that means GM assembled. If it hasn't been to badly modified, then the house fuses are all in that electrical cabinet
in the passage. If that is where they are, them that is also a distribution point for the house power. The converter is right there too. Easy thing
to would be to tie the little solar to the output of the converter. Then you know you are in the right place and have both sides connected.

You got Lifeline GPL-6s for 125C$??
Well, these days you have to wear a mask, but did you have a gun too???

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
You must log in or register to reply here.
Get your shine on at www.cruzingear.co
GMCMI Spring 2026 Rally

Share this page

Share this page
Top Bottom
Back