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Old 11-24-2019, 06:04 PM   #1
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Default Alternator upgrade

Just ran a Test on the 250 Amp GM Alternator that I had installed (vs 145 Stock). Ran a 2/0 Welding Cable to the Bank of 4 AGM Batteries (5400 Watts) at rear of the Van. Fused at 200 DC Amps. Deliberately pulled down the House Batteries to 50%. As my Brother started the Van, I measured 167 Amps to the thirsty Batteries. As I’m a Full-timer, simply driving the Van will keep the Batteries at a high SOC. The Solar (400 Watts) will now just keep them topped off. Money well spent 👍
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Old 11-25-2019, 04:29 AM   #2
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Just ran a Test on the 250 Amp GM Alternator that I had installed (vs 145 Stock). Ran a 2/0 Welding Cable to the Bank of 4 AGM Batteries (5400 Watts) at rear of the Van. Fused at 200 DC Amps. Deliberately pulled down the House Batteries to 50%. As my Brother started the Van, I measured 167 Amps to the thirsty Batteries. As I’m a Full-timer, simply driving the Van will keep the Batteries at a high SOC. The Solar (400 Watts) will now just keep them topped off. Money well spent ��
Please, more details for those of us with the Express chassis and 6.0L.

Straight swap (no change to pulley's or belt)? Price? Part number?

Thanks, Roy
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Old 11-25-2019, 01:09 PM   #3
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Please, more details for those of us with the Express chassis and 6.0L.

Straight swap (no change to pulley's or belt)? Price? Part number?

Thanks, Roy

The alternator in the pic says Delphi so would likely be a GM based aftermarket unit.



We have a DC Power 250 amp in our 07 Chevy that was drop in. Nations sells them also I think. They are hairpinned wound which is a good feature.


167 amps at 50% is similar to what we got on the 250 amp when it was the only one in place. I think we would initially flash up to over 200 amps and then settle in the 180 range IIRC and be 170ish hot. Our 440ah of Lifeline AGMs can just handle 180 amps continuous charge but heat about 15* read at the post.


Angelroman is running at about 67% capacity so it is very likely he may get in to heat issues so should be checked to see hot hot it gets, hood down idling after driving a bit. Open the hood and quickly check. Ours hottest at the laminations in the center and at the rear diodes. Infrared heat thermometer works well. Going over 220*F is not a good idea and is where the Balmar regulators cut back to 50% output for reference.



Chevy alternators are in a quite poor place for heat as they see a lot of radiator heat going down the road when hot. I have gauges on bot of ours and they will be at 150*F sometimes even at low output when it is hot out and going down the highway.


The alternators changed in around 2007/2008 from internal regulator to computer regulator, so that is a consideration to take into account.
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Old 11-25-2019, 03:37 PM   #4
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I've felt the 145Ah standard alternator on the Chevy Express 3500 is pretty marginal for an application with the added demands of charging the coach batteries. Surprised they didn't come equipped with something 30-40 amps larger.

In my case, I use a 40A DC to DC charger for my lithium upgrade, so my coach demand should be limited to that, right? However, as I mention in my upgrade thread, I sometimes notice at cold startup and when m alternator is charging both engine and coach batteries, a drop in voltage below 12 volts on my cigarette-lighter plugin gauge at idle.

Assuming that indicates the alternator is sometimes struggling with my current set up, wouldn't upgrading the alternator would be a cost-effective way solve the issue without the need for radical modifications?
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Old 11-25-2019, 04:05 PM   #5
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If this is new since the switch over to Lithium then look into cable size, grounds, losses due to other sources of resistance etc. all come into play. Maybe check all of that first.

A steel washer mistakenly put under a copper lug for example would cause noticeable resistance with large loads.
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Old 11-26-2019, 12:47 AM   #6
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If this is new since the switch over to Lithium then look into cable size, grounds, losses due to other sources of resistance etc. all come into play. Maybe check all of that first.

A steel washer mistakenly put under a copper lug for example would cause noticeable resistance with large loads.
Thanks. I did have to make a chassis ground for the new 40A DC to DC charger (there was no negative from the engine battery in the stock setup to use for my upgrade). I used a large steel 1/2" diameter bolt that was one of two that fastened a heavy cabinet bracket down through the rear wheel well. I anticipated that the nearly 1" of threaded connection would make an excellent contact for the 4 ga. cable. But since the bolt was larger than the 3/8" cable lug, I drilled and added a thick aluminum angle piece as a connection block to bolt the cable through. I will revisit that.

EDIT: If I used something like this, would it be better? Says it's nickel-plated aluminum. Would have to drill it out to 1/2" or find it in a larger diameter.

https://www.ebay.com/itm/Nickel-Plat...72.m2749.l2649
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Old 11-26-2019, 01:09 AM   #7
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A very common place for voltage drop is actually in the negative return route to the engine which will mostly go through the braided flex cable from the engine to frame rail. They are often right in salt and slop and also in any oil drippings. For big alternators, they are also undersize, but for 40 amps you are likely fine with size, but may have the voltage drop from bad connection or broken braid. The other thing to remember is that on a body on frame van, the body is electrically isolated from the frame from the the factory. There will be a small wire from the fenderwell to the battery or engine on the passenger side on them if they are like ours. That wire is probably no more than a 8ga or so, I think, so won't carry a lot of current from either a battery charger or alternator that uses the body as a return route. A lot of class b conversion wind up with some conducting paths during the conversion from brackets and such, but checking for voltage drop in the small wire from the body to battery might show drop, in which case you would want to upsize the wire and run a big cable from the frame to the body somewhere.
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Old 11-26-2019, 02:13 AM   #8
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Wow..what does 5400 watts of AGM weigh??
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Old 11-26-2019, 02:18 AM   #9
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Wow..what does 5400 watts of AGM weigh??

That is just about the same size as our 440ah AGM bank of Lifeline batteries which is listed at 66# each, so 264# total.
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Old 11-26-2019, 03:44 AM   #10
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A very common place for voltage drop is actually in the negative return route to the engine which will mostly go through the braided flex cable from the engine to frame rail. They are often right in salt and slop and also in any oil drippings. For big alternators, they are also undersize, but for 40 amps you are likely fine with size, but may have the voltage drop from bad connection or broken braid. The other thing to remember is that on a body on frame van, the body is electrically isolated from the frame from the the factory. There will be a small wire from the fenderwell to the battery or engine on the passenger side on them if they are like ours. That wire is probably no more than a 8ga or so, I think, so won't carry a lot of current from either a battery charger or alternator that uses the body as a return route. A lot of class b conversion wind up with some conducting paths during the conversion from brackets and such, but checking for voltage drop in the small wire from the body to battery might show drop, in which case you would want to upsize the wire and run a big cable from the frame to the body somewhere.
Ok. I will check for ground connections under the hood too. Will also see if I can locate a body to frame ground like you mention.
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Old 11-27-2019, 06:41 PM   #11
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Thanks booster for all your previous advice.

A couple of points were raise...

“The alternator in the pic says Delphi so would likely be a GM based aftermarket unit “...booster.

Correct. Drop-in Delphi. Same Pulley. $230. The Alternator was sourced from a local Vendor when the Van underwent extensive Preventive Maintenance (Belts, Hoses, Thermostat, Coolant, Full Synthetic Oil, Transmission Fluid), etc. Also, new A/C Compressor and Tensioner.

“67% Capacity” ...booster

Question. Just so I understand, how did you arrive at that number? With daily driving and Solar, I’m usually at 90-95% when I’m parked for the evening. There is a separate 300 Watt Pure Sine Inverter that powers the Media Cabinet (TV, DVR, Blue-ray). It is on 24-7 (Regularly Recording Programs/Movies). So with the Inverter, Fan, Monitors, a few lights before Bed, usually at 80-85% in the morning. Batteries are under 3 years old. No noticeable loss in Capacity.

“There will be a small wire from the fenderwell to the battery or engine on the passenger side on them if they are like ours. That wire is probably no more than a 8ga or so, I think, so won't carry a lot of current from either a battery charger or alternator that uses the body as a return route. A lot of class b conversion wind up with some conducting paths during the conversion from brackets and such, but checking for voltage drop in the small wire from the body to battery might show drop, in which case you would want to upsize the wire and run a big cable from the frame to the body somewhere”...booster

Should I increase that wire (I have a short piece of 4ga) or something even larger at another Location? What size Gauge?

Going to add a “Infrared Heat Thermometer” to my Tool Box .

Thanks again .
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Old 11-27-2019, 07:34 PM   #12
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Thanks booster for all your previous advice.

A couple of points were raise...

“The alternator in the pic says Delphi so would likely be a GM based aftermarket unit “...booster.

Correct. Drop-in Delphi. Same Pulley. $230. The Alternator was sourced from a local Vendor when the Van underwent extensive Preventive Maintenance (Belts, Hoses, Thermostat, Coolant, Full Synthetic Oil, Transmission Fluid), etc. Also, new A/C Compressor and Tensioner.

“67% Capacity” ...booster

Question. Just so I understand, how did you arrive at that number? With daily driving and Solar, I’m usually at 90-95% when I’m parked for the evening. There is a separate 300 Watt Pure Sine Inverter that powers the Media Cabinet (TV, DVR, Blue-ray). It is on 24-7 (Regularly Recording Programs/Movies). So with the Inverter, Fan, Monitors, a few lights before Bed, usually at 80-85% in the morning. Batteries are under 3 years old. No noticeable loss in Capacity.

“There will be a small wire from the fenderwell to the battery or engine on the passenger side on them if they are like ours. That wire is probably no more than a 8ga or so, I think, so won't carry a lot of current from either a battery charger or alternator that uses the body as a return route. A lot of class b conversion wind up with some conducting paths during the conversion from brackets and such, but checking for voltage drop in the small wire from the body to battery might show drop, in which case you would want to upsize the wire and run a big cable from the frame to the body somewhere”...booster

Should I increase that wire (I have a short piece of 4ga) or something even larger at another Location? What size Gauge?

Going to add a “Infrared Heat Thermometer” to my Tool Box .

Thanks again .

I assume that is new Delphi, not a remanuctured?


The 67% of capacity is the 167amps you measured compared the rated amps of the alternator, so the % of capacity of the alternator. Stock alternators often have heat issues above 50% if you run for a while, probably 15 minutes or so, at that high an amperage. That is why you would need to get a good look at how hot it is actually running. I assume you were looking at the battery monitor which wouldn't show what the van was using, so you probably were another 15 amps above the 167amps you saw.


The need to upsize the fenderwell wire is really determined by how much stuff has the grounds hooked up to the body that have to get back to the frame to complete the circuits, so a bit confusing. Basically, unless the batteries, alternator, shore charger, and solar are grounded to either the body or chassis you need some connections. If the batteries are connected to the frame with their negative, you would need to confirm good connection at the engine to frame to complete the alternator circuit. That is the braided cable under the van I mentioned earlier. If the shore or solar charger are not grounded to the frame, but to the body, then you would need to upsize the fenderwell wire. 4ga should be plenty unless the batteries are grounded to body, in which case you a 2ga or larger. I connected the body and frame under the rear using 3/0 cable and some of the big bolts already there as it was an easy place to do it.
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Old 11-27-2019, 08:33 PM   #13
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What is a good source for this alternator? This sounds like a great bang for the buck charging upgrade.
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Old 11-27-2019, 09:37 PM   #14
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Hey booster

“ The 67% of capacity is the 167amps you measured compared the rated amps of the alternator, so the % of capacity of the alternator”...booster

Ok. I misunderstood. I thought you were speaking of remaining Battery Capacity.

My understanding is that the Batteries will only “Accept” the Amps they want, regardless of how many Amps are thrown at them (Excess Amps are given off as heat). To put it another way, if the Batteries were discharged to 40%, the “167” measured would have been higher. If this is incorrect or under-informed, please advise.

It is a new Delphi Alternator (Was told I got the “Vendor“ discount). Who knows?....

I will upgrade the “Fenderwell” wire to 4ga. As you suggested, I will pickup a short piece of 3/0 and look for a spot at the rear of the Van for the “Body to Frame” Ground.

Thanks again
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Old 11-27-2019, 10:18 PM   #15
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Hey booster

“ The 67% of capacity is the 167amps you measured compared the rated amps of the alternator, so the % of capacity of the alternator”...booster

Ok. I misunderstood. I thought you were speaking of remaining Battery Capacity.

My understanding is that the Batteries will only “Accept” the Amps they want, regardless of how many Amps are thrown at them (Excess Amps are given off as heat). To put it another way, if the Batteries were discharged to 40%, the “167” measured would have been higher. If this is incorrect or under-informed, please advise.

It is a new Delphi Alternator (Was told I got the “Vendor“ discount). Who knows?....

I will upgrade the “Fenderwell” wire to 4ga. As you suggested, I will pickup a short piece of 3/0 and look for a spot at the rear of the Van for the “Body to Frame” Ground.

Thanks again

You are absolutely correct that the batteries will only accept what they are able to absorb, and thus control the charge rate if surplus charging current is available. It is probably that the the 167 would go up if the batteries were lower, but I think maybe not because of the load from the van making the alternator output closer to 190 amps. I think the alternator will quickly heat up and not do much more than that once hot, but it depends on the alternator design.


That said on your battery bank, it it reacts like our Lifelines, it is likely that anything more than 180 amps is going to get the temp up too much on them for long life. That is what we have found. We could run 280 to them from our 530amps of alternators but they were only good for about 15-20 minutes before they started to get too warm. Good for a quick recovery in a short time, but not longer. Since in real camping we never used the high rate setting, I have now dialed it back to 120 amps on normal charge and 180 amps on fast charge. Safer and less attention needed, with no loss of usability the way we use our van.
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Old 11-28-2019, 12:06 AM   #16
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“ I have now dialed it back to 120 amps on normal charge and 180 amps on fast charge”...booster

Really interesting. How are you able to do this? What Hardware was used?

Thanks again
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Old 11-28-2019, 12:12 AM   #17
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“ I have now dialed it back to 120 amps on normal charge and 180 amps on fast charge”...booster

Really interesting. How are you able to do this? What Hardware was used?

Thanks again

I have an an Ample Power remote regulator controlling our alternators which are 530ah in parallel with van systems. It has two different setback levels, which is very useful for stuff like this. Unfortunately, they have discontinued them so now the only option is really the Balmar remote that has two methods of reduction, but on fixed at 50% and one adjustable above 50%. Ours, and the Balmar if you chose to, can be switch controlled, which we do. What the Balmar doesn't have, that we do, is the ability to lock into absorption until we see the batteries are full, which is a great feature. It is also switch controlled on ours.
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Old 11-28-2019, 11:11 PM   #18
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After eating entirely too much Turkey, Ham and Sides (Dessert will be later. MUCH later ), went out to the Van and preformed another Test. Batteries at Rest were 95% (Turned off Solar earlier).

Started Van. Peak Amps were 29. Quickly tapered down to 18, then15, when the Test was ended.

I spend 6/7 months a year in Key West. There are several days a month (As many as 20) when the Van is driven less than 20 miles. Not nearly enough to maintain a high (90%) SOC, even with 400 Watts of Solar. With this upgrade, having the capacity to Bulk Charge at a much higher Rate, I believe it won’t be an issue. We’ll see this coming Season
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Old 11-28-2019, 11:29 PM   #19
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After eating entirely too much Turkey, Ham and Sides (Dessert will be later. MUCH later ), went out to the Van and preformed another Test. Batteries at Rest were 95% (Turned off Solar earlier).

Started Van. Peak Amps were 29. Quickly tapered down to 18, then15, when the Test was ended.

I spend 6/7 months a year in Key West. There are several days a month (As many as 20) when the Van is driven less than 20 miles. Not nearly enough to maintain a high SOC, even with 400 Watts of Solar. With this upgrade, having the capacity to Bulk Charge at a much higher Rate, I believe it won’t be an issue. We’ll see this coming Season

400 watts of solar in Key West should give you some pretty good output, unless it is cloudy a lot there (I have no idea if it is). How much power a day do you use?
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Old 11-29-2019, 01:00 AM   #20
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Hey booster

The Batteries are in Float by mid-day in KW. If there are several consecutive days of mostly Cloudy Skies (It happens ), the Solar Controller reads MPPT frequently. After parking for the evening, I’ll run Lights, Fan, Convection Oven, TV, DVR, Laptop Computer, Large Inverter, charge Phone. Usually at 60-65% by morning. I’m expecting the higher Capacity Charging will increase the morning average SOC

Thanks again
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